## Military Float Bridging Equipment Headquarters, Department Of The Army Distribution Restriction: Approved For Public Release; Distribution Is Unlimited.

Headquarters Department of the Army Washington, DC, 27 December 1988

## Military Float Bridging Equipment

PREFACE
The purpose of this Training Circular is to provide a comprehensive reference for the use of military floating equipment in support of river crossing operations. It is intended for use by engineer officers and noncommissioned officers at all levels. The intended purpose is to provide guidance for the tactical employment of river crossing equipment to include critical planning considerations, methods of employment, and steps in the design and construction of floating rafts and bridges, anchorages, floating protective devices, and fixed bridge spans constructed from float bridging equipment.

The proponent of this publication is HQ TRADOC. Submit changes for improving this publication on DA
Form 2028 (Recommended Changes to Publications and Blank Forms), and forward it to Commandant, US
Army Engineer School, ATTN: ATZA-TD-P, Fort Belvoir, VA 22060-5291.

Unless otherwise stated, whenever the masculine gender is used, both men and women are included.

DISTRIBUTION RESTRICTION. Approved for public release; distribution is unlimited.

*This publication supersedes TM 5-210, 3 August 1970.

## Chapter 1. River Crossing Concepts

severe obstacle. The methods available for conducting a hasty crossing include the use of
Existing bridges or civilian ferries Armored vehicle launched bridges (AVLBs)
Amphibious vehicles Ford sites Organic rafting/bridging equipment Where these crossing means are available in sufficient quantities to quickly cross the bulk of the advancing forces, a hasty river crossing should be strongly considered as a feasible method of crossing the water obstacle.

METHODS OF CROSSING RIVERS
River crossing operations have always been an integral part of land warfare. From Alexander the Great's crossing of the Hydaspes River in
326 BC, to modern times, an army's ability to cross significant water obstacles has often led to the success, or failure, of that army. The lethality of modern weapons and the capabilities of larger enemy formations have mandated that US forces adapt an AirLand Battle doctrine which relies heavily upon our ability to maneuver. The ability of the US Army to cross rivers quickly and efficiently is critical to the success of this doctrine. Field Manual
(FM) 90-13 prescribes three types of river crossing operations: the hasty, deliberate, and retrograde crossing. A basic understanding of each of these crossing methods is essential to a commander's ability to employ his available river crossing assets.

Hasty A hasty crossing is a decentralized operation using organic, existing, or expedient crossing means. This type of river crossing is conducted as a continuation of the attack and results in little or no loss of momentum by the attacking force. Because of this, the hasty river crossing is the preferred method of negotiating water obstacles. The hasty crossing can normally be accomplished in situations where the enemy's defending forces are weak, or confused, and in cases where the river does not constitute a Deliberate In situations where the hasty river crossing is infeasible, or when a hasty crossing has failed, the deliberate method must be executed. A
deliberate crossing is not usually conducted from the march, but requires a buildup of firepower and river crossing equipment. Inherent in the conduct of such a crossing is the need for detailed planning and centralized control. The deliberate crossing is a three-phased operation consisting of an assault phase, a rafting phase, and a bridging phase. The methods available for conducting a deliberate crossing may include all of the means provided in a hasty crossing, as well as the addition of Corps rafting and bridging assets. The selection of crossing

## River Crossing Concepts 1

sites is an essential part of the employment of these assets.

Retrograde Unlike the hasty and deliberate methods of crossing rivers, the retrograde crossing is a defensive operation. The retrograde crossing is conducted in situations where the enemy's advances threaten to overwhelm the friendly forces. In such cases, the retrograde crossing is conducted with the intention of protecting the retrograding force and establishing a viable defense along the exit bank of the river.

Retrograde crossings present a high risk to the retrograding force and are characterized by
Enemy control of the maneuver initiative Detailed planning Centralized control A delaying action against the enemy's advance, as an attempt to trade space for time at the crossing sites.

Ideally, the retrograde crossing is conducted in a way which will force the enemy to conduct a deliberate river crossing. The commander must consider all available crossing means in planning this type of river crossing operation.

SELECTION OF CROSSING SITES
Crossing site selection is a critical step in the execution of a river crossing operation. This Additional characteristics for the use of specific crossing means include

## Avlbs:

For M113s: (APC)
Narrow gap (57 feet for unprepared abutments) Firm banks on both shores selection must be based upon a detailed reconnaissance of the river and a keen understanding of the overall tactical plan. Crossing sites are generally characterized as either assault, rafting, or bridging sites. Since it is unlikely that any one site will have all of the desired characteristics, every available site must be carefully analyzed. Ultimately, the sites which best support the tactical plan should be selected.

Uphill grade of 28 percent or less For assault boats:
Downhill grade of 19 percent or less Transverse grade of 11 percent or less

## Ford Sites: See Table 1 On Page 3. Swimming Sites And Assault Boat Sites: Minimum Exposure To Enemy Direct Fire Weapons Covered And Concealed Access To The River

Assault In the assault phase of a deliberate river crossing the commander attempts to cross sufficient combat power to secure the far shore of the river. The commander designates initial far shore objectives which must be seized to accomplish this task. The assault forces may cross the river by fording, swimming amphibians, or by using AVLBs, assault boats, or army aircraft.

With the exception of the latter, each of these crossing means requires the selection of a suitable assault crossing site. All assault sites should be located in a position where
Rafting In the rafting phase of a river crossing operation, the commander reinforces assault forces with armored vehicles and antiarmor weapons.

Ribbon rafts are heavily relied upon to accomplish this task. The M4T6 and Class 60
rafts, as well as light tactical rafts (LTRs), may also be used when sufficient ribbon assets are unavailable. All raft sites should
Be positioned downstream of proposed bridge sites.

Enemy forces are weak.

Gently sloping, firm banks which permit rapid entry and exit at multiple points along the river Narrow point along the river Bank slopes of 30 percent or less Be placed in locations which provide the fastest access to the initial far shore objectives.

There is dominant terrain on the friendly shore from which the assault can be supported by overmatching fires. There is concealment from enemy observation.

Have well established road networks leading to them on the near shore and acceptable routes of egress on the far shore.

Have firm banks on both shores with slopes of 0 to 20 percent where possible.

There are adequate routes to the river, as well as routes away from the river, towards the initial objectives.

When selecting these sites it must be understood that vehicles and boats will drift downstream while attempting to negotiate the water obstacle. Generally, the degree of drift is based upon the swim speed of the vehicle and the current velocity of the river. More specifically
The current velocity of the river is slow (0 to
5 feet per second (FPS) is desirable).

Be located on a narrow point along the river which is free of sandbars or other obstacles which might impede rafting operations.

## River Crossing Concepts

Be placed in locations where the current velocity of the river is slow. Currents of 0 to
5 FPS are desired. Currents greater than 10
FPS are considered to be unacceptable.

Provide depth of water greater than the draft of the floating raft to be used at that site. See Table 2.

Bridging As a river crossing operation progresses, the crossing force commander will use floating bridges to cross the bulk of the advancing force.

Ribbon equipment will be used extensively in this role. The M4T6 and Class 60 bridges may be constructed along proposed main supply routes (MSRs) to provide lines of communications for the advancing forces. All bridge sites should
Be located upstream of raft sites. Be constructed at sites with well established road networks on both sides of the river.

Have firm banks with slopes of  to 10 percent where possible. If banks are not firm, units may use the Access/Egress Roadway System (AERS). See Appendix F.

Be located along a narrow portion of the river and in a position where currents are no greater than 10 FPS (0 to 5 FPS is preferred).

Provide depth of water greater than the draft of the floating bridge to be used at that site. See Table 3 on page 4.

The need for adequate assembly sites must also be considered when establishing abridge site. The size and number of assembly sites vary with the type and length of the bridge to be built and with the method of construction that is used. Subsequent chapters provide additional guidance regarding launch and assembly sites for specific types of floating bridges.

## Chapter 2 Watermanship And Safety

WATERMANSHIP
Watermanship is defined as the art of handling a boat or raft afloat. Although the basics of watermanship can be explained in this manual, watermanship skills can only be attained by extensive training under varied conditions. This section provides those personnel who operate or supervise the operation of watercraft with applicable navigation rules, and gives an appreciation of some of the forces which act upon those craft under different river conditions.

6. When two vessels are approaching each
other at right angles or oblique angles, the
vessel which has the other on the left (port)
side is considered to be the
PRIVILEGED vessel and will maintain
course. The second vessel which has the
other on the right (starboard) side is
considered to be the BURDENED vessel and must keep out of the way. The
5. When two vessels are approaching each
PRIVILEGED vessel shall give one blast
other head on, or nearly head on, each vessel
of the horn or whistle, and the
should swing to the right (starboard). Always
BURDENED vessel shall respond with
attempt to pass left side (port) to left side
one blast.
(port). Both vessels give one blast of the
7. If for some reason two vessels are on a
horn or whistle.
collision course and it seems more suitable
Navigation Rules
It is the duty of the commander of any craft to
avoid collisions at all times. Navigation rules are
established to provide for the safe operation of
ships at sea or ships and boats in inland waters.
They apply to all vessels except those which are
anchored, aground, or made fast to the shore.
All operators should be familiar with the following rules:
1. Maintain a reasonable speed when operating
among other craft.
2. Attempt to keep to the right (starboard) side
of any channel.
3. By law, most vessels will display at least four
lights:
white masthead light green starboard light red port light white stem (rear) light
4. The following whistle or horn blasts are
considered standard
danger signal (four or more short blasts).
9. Powered craft always give way to sail craft.
10. All craft will give way to a vessel that is
restricted in its ability to maneuver.
11. During tactical operations
Craft proceeding across a river in the direction of the enemy have right of way. Returning craft must always give way.
Handling of Boats The movement of a craft on the water is affected by the speed and direction of the current, the strength and direction of the wind, and the capabilities of the craft's system of propulsion. Of the three, the boat commander can only control the power of the boat propulsion.

The commander must exercise judgment with regard to the effects of wind and current on the craft to obtain the greatest advantage or least degree of obstruction.

Boats and tugs will give way to all rafts and amphibians. Power boats will give way to boats that are paddled. When in doubt, however, the smaller craft must give way to the larger.

Current Consider first a straight stretch of river as shown below. Note in A that when the boat is steered from the start so that the bow is pointing continuously to the landing place, it will be

to pass right side (starboard) to right side
(starboard), then the PRIVILEGED
vessel shall swing to the left (port) and give
two blasts of the horn. The signal shall be
answered with two blasts from the BURDENED vessel which shall also swing
to the left (port).
8. When one vessel is overtaking another
vessel headed in the same direction, she
shall ask permission of the slower boat to pass either side by signaling one blast for
starboard, or two blasts for port. The
overtaken boat shall give permission by
answering with the same signal. If for some reason permission cannot be given, the
overtaken boat shall answer by giving the
craft and that of the load that is exposed to the wind. Since this exposed area changes as the craft's course changes, and since the strength of the wind is rarely constant, the effect of the wind will vary continually. It is the raft commander, more than the boat commander, who will be most affected since the surface area of a boat and the occupants exposed to the wind is usually small.

Consider the more difficult problem of crossing a fast flowing river at a bend or turn. The current in this case is usually greatest near the bank on the outside of the bend. Quite often a reversal of current will be encountered near the bank on the inside of the bend. When crossing from the inside of the bend, it may be best to first gain ground upstream by keeping close inshore where the current is slack and then to go straight across to the other bank, swinging at the last moment to come alongside the far bank against the current.

Wind The effect of the wind on a watercraft is directly proportional to the surface area of the swept downstream by the current and the course will arc as shown. The last part of the trip, in this case, must be made almost totally against the current.

A better method of crossing this river is with the bow of the boat pointing somewhat upstream of the landing place so that the boat's course is as shown in B. This course is best maintained by identifying two sighting marks on the far shore, and keeping in line with those marks.

If it is necessary to cross the river as quickly as possible and a choice of launching sites is permitted, launch the boat upstream of the landing place and then across at right angles to the current as shown in C.

Propulsion Inexperienced boat operators must first understand that boats do not react in the same manner as a car. All movements take additional time since the grip which is maintained between the skin of the boat and the water is not nearly as strong as that which exists between the tires of a car and the road. The heavier the boat, the longer the boat's reaction time.

Generally, the faster a boat moves through the water, the easier it is to control. When going downstream, the speed of the boat relative to the banks can give a false impression of speed through the water. Unless the craft commander remembers this, there is a temptation to reduce the power output of the boat's engine/motor with a consequent loss of control. A
downstream crossing can best be made by heading the craft upstream and keeping her moving forward relative to the water while allowing the current to carry her downstream relative to the banks. By using this method, control of the boat can be maintained at all times.

## Dropped Overboard. Steering Lines Must Be Rigged As Tight As Possible To Maintain The Correct Centerline Alignment Of The Boat And Raft. Warning! Never Use Steel Cables As Steering Line. During An Emergency The Operator May Be Unable To Cut Steel Cable, Resulting In Loss Of Life And Equipment.

Rafting Operations The principles regarding the effects of wind and currents on boats also hold true during rafting operations. A raft moves and steers differently from a boat for two reasons. First, it is usually heavier and therefore takes longer to start and stop. Secondly, partly because of the weight and shape, it has a much greater reluctance to start turning, and once turning, to stop, A boat will tend to move straight ahead under power. A raft, on the other hand, may continually tend to rotate or swing unless the raft commander is constantly alert to such movements.

4. The exact positioning of boats will depend
upon the rafting method selected. More precise guidance for the exact methods of
tying boats to specific rafts is given in the
rafting section for each particular type of
floating equipment.
Loading and unloading of rafts The loading and unloading of rafts can be the most difficult part of a rafting operation. The approaches to the raft may be slippery or somewhat steep. Deck space is limited and there is a danger of the loaded vehicle overshooting or driving off the side of the raft's roadway. Often, the raft will tilt during loading with the possibility of the inshore boat and bay grounding, or even sinking.

Prior to loading vehicles onto a raft, the raft commander must ensure that
Vehicle dimensions (length, width and classification) do not exceed the capabilities of the raft.

Attaching boats to rafts
Bridge erection boats (BEBs) may be used to
propel rafts in support of river crossing operations. The connection of the boat to a raft is the first major step in proper operation of the raft. Rafts are normally pushed rather than pulled.
This permits a shorter turning radius with positive backing of the raft and the direct application of steering power to the raft. In large bodies of rough water it may be more advantageous to tow rather than push the raft.
Some general rules for the rigging of boats to
rafts are as follows:
1. Boats are in forward gear at idling speed
when lines are rigged.
2. Wet all lines prior to use to minimize
stretching.
3. Steering lines are most important in
controlling a raft. They are made of the newest and best rope available and of
sufficient size. Normally, 7/8-inch diameter
polypropylene rope is used. This rope is
durable and easy to handle and will float if
The raft is secured to the shore with tag lines or approach guys. These lines help to prevent the raft from moving away from the shore, or swinging left or right when

## Watermanship And Safety

vehicles are loaded. The thrust of the boats will also be required to prevent raft movement during loading.

All crew members are in position and are prepared to load the raft.

The operators of the loaded vehicles understand the hand signals which will be used to control the loading of the raft. Some signals which might be used are shown on page 9.

Normally, position vehicles on rafts so that the center of gravity of the vehicle is slightly to the downstream side of the raft centerline, and slightly to the rear (shore side) of the raft. This maximizes the raft's freeboard. Freeboard is the distance from the waterline to the top rim of the raft or boat. Inadequate freeboard will cause the raft to swamp once the raft is underway.

When loading more than one vehicle on a raft, normally load the heavier vehicle last (toward the rear of the raft). Ensure that the overall center of gravity of the load is slightly to the downstream side of the raft centerline, and to the rear of the raft. Once vehicles are positioned, place chock blocks in front of and behind the wheels to prevent vehicle movement in the event of any sudden raft movement.

Methods of rafting All US heavy floating rafts are propelled using BEBs. There are two methods of attaching these boats to rafts prior to rafting operations:
conventional and longitudinal.

the raft to drift downstream. The angle at which the raft is propelled will vary with the velocity of the river. Guidelines to be followed when physically attaching boats to rafts are provided in the appropriate rafting section for each type of floating equipment.

Longitudinal. When rafting in a longitudinal configuration, one boat is tied off to each side of the raft, parallel to the raft's roadway. Use of this method is normally limited to ribbon rafts.

Because the longitudinal method of rafting Conventional. When rafting in a conventional configuration, all boats are tied off to the downstream side of the raft, perpendicular to the raft's roadway. The conventional method is always used to propel M4T6, Class 60, and light tactical rafts. Ribbon rafts may also use this method. When leaving shore, the raft should be backed out at a slight angle with the bow of the boat upstream. When there is enough room to turn, steer riverward and move ahead. In crossing a river, head the raft into the current at an angle so the force of the current does not cause generally allows for faster, more efficient operation, longitudinal rafting is normally the preferred method when using ribbon equipment. Some factors which may influence the decision to raft longitudinally or conventionally when propelling ribbon rafts are provided in Chapter 4.

Note. Longitudinal rafting cannot be used when the river current in the loading and unloading areas exceeds a velocity of 5 FPS.

Controlling raft movements It is impossible for the boat operators to independently control the direction and speed of raft movements. Because of this, the raft commander must accomplish this task. In order to give directions to the boat operators, the raft commander should be located in such a position that the river and shoreline can be observed in the direction of movement, and where the boat operators can clearly see all signals given. (See below.) These signals apply whether boats are used alone or in combination. It is critical that the raft commander understand not only rafting operations, but also the principles of maneuvering the BEBs.

direction of the raft changes from the direction of the current. Turns in such a restricted channel should be attempted only when absolutely necessary, and then, only by experienced operators.

decided upon. It may be necessary to rig lines to assist in pulling the raft from an obstacle. If a raft is grounded high, it may be possible to anchor it to the obstruction, release a boat, and allow the boat to drop anchors downstream.

The boat could then be rerigged to the raft and the engines used to pull the raft free. Additional boats or winches rigged from vehicles on the banks may be used to assist in freeing grounded boats or rafts.

Operation above obstacles. When operating rafts above bridges, dams, mine booms, or other obstructions extending across a river, sufficient room must be allowed for maneuvering and positive action in the event of an emergency. In fast water (currents greater than 5 FPS), light rafts and boats should remain 400 to 900 feet above any obstacle. Heavy rafts should allow at least 1,800 feet as a minimum safe distance.

Downstream through a channel. The speed of the raft together with the speed of the current causes abrupt changes of direction when traveling through a narrow, swift channel. There is little time for the raft commander to react and control the raft. A mistake in estimating speed downstream can seldom be corrected as most boats do not have the power to stop a loaded raft from grounding in a high velocity current.

Due to the speed of the raft and narrow width of channels, there is frequently insufficient room to swing the raft. If a corner of the raft grounds, the raft will turn crosswise to the current and often capsize. It is necessary that the raft commander decide upon possible courses of action through the entire channel prior to initial entry. Once the raft has entered, there is little choice. The dependability of equipment and the care with which the boat has been rigged to the raft are of utmost importance when rafting in swift streams and narrow channels.

Rafting operations under special conditions River bends or near obstructions. When operating a raft or any type of boat in swift water, it is essential to understand the flow of water in an open or natural channel. The current flow in a curved channel causes the water to pile up to the outside of the bend, depending upon the sharpness of the curve. This causes the river to run much faster on the outside of the bend than on the inside. The composition of the riverbed may be such that erosion occurs, forming sandbars and shelves. Such sandbars or shelves may be seen from a distance by observing the surface action of the water. The peculiarities of such surface action can be learned only by actual observation and experience. In some riverbeds, sandbars are found in unexpected places having been formed by large rocks, trees, or other debris which have become freed to the riverbed. Frequently, there are whirlpools just above and below such obstructions. These whirlpools are exceptionally dangerous to the operation of rafts, especially when rafts are lightly powered or where sufficient steering power may not be available.

When such a current or obstruction is encountered, it is generally best to stay in the swiftest part of the current and proceed with caution until the direction of the flow of the current is determined and the danger point is passed. If the direction of the raft is changed, it must be done with caution since the steering power must be positive and powerful when the Grounding. An experienced operator can control the grounding of a boat or raft in swift currents. If a boat or raft is going upstream, the throttle/scoops must be adjusted immediately to hold the boat or raft steady and keep it from drifting downstream thus preventing further damage to the raft or boat. Check damage immediately and, if possible, make repairs. The extent of the obstruction is then determined and a plan for removal of the raft or boat must be SAFETY
Safety is always a primary consideration when soldiers are required to work near or over the water. Because of the variety of missions that can be performed around the water and because no two rivers are exactly alike, it is difficult to prescribe safety guidelines which can be applied to all, or even most, situations. The Department of the Army has therefore instructed that all subordinate commands establish a standard operating procedure (SOP) for water safety. Army Regulation (AR) 385-15 requires that this SOP be based upon the missions required of each respective unit, and on the environmental conditions under which each unit is expected to perform the mission. Some considerations to assist in the formulation of an SOP are provided in subsequent paragraphs.

## Waterrnanship And Safety

personnel are aware of the contents of the SOP, and to ensure that personnel follow the SOP during all operations.

Personnel Personnel required to work near or around the water should be capable of meeting the minimum swimming standards in FM 21-20 and should periodically receive drownproofing training to ensure these standards are maintained. In situations where nonswimmers must work over the water, these personnel should be identified beforehand and paired with a "buddy" who is a strong swimmer.

All personnel required to work over the water should be provided with a life jacket or life vest.

Personnel should be inspected prior to waterborne operations to ensure that the vests are properly worn and fitted.

Personnel working near or over the water should unblouse the trousers from their boots.

Overshoes should not be worn when working over the water.

All personnel should receive a safety briefing prior to the conduct of waterborne operations. This briefing should explain to the soldiers any hazards which might exist around the work site, such as particularly swift currents, shoals, sandbars, or other obstructions in the water, and any dangerous weather conditions such as high winds or low visibility. The briefing can also be used to train or retrain soldiers in skills such as the emergency/man overboard drills, watercraft discipline, methods of signaling the safety boat in an emergency, and first aid.

The commander should designate a safety officer who is responsible for the conduct of operations near or over the water. This safety officer's primary responsibilities are to ensure that the safety SOP is adequate, that all unit safetv boat crew must be a strong swimmer
(preferably trained in lifesaving techniques).

The safety boat should be equipped, as a minimum, with the items listed in Table 4. The designated safety boat should perform no duties other than to standby, usually downstream from, but within a safe distance of the work site. The safety boat may also be required to warn off civilian craft or other vessels which might create a hazard or might otherwise interfere with the conduct of the operation. In situations where the waterway is extremely busy, when the current velocity is swift, or where the work parties are quite large or spread over a great distance, the commander might be required to designate more than one safety boat for each work site.

Safety Boats When conducting operations over the water, the commander should always consider designating one of the watercraft as a safety boat. This boat must be large enough and powerful enough to cope with the conditions at the work site. The safety boat should be crewed by at least two persons who are qualified and experienced helmsmen. Both crew members should be trained in the correct methods of recovering personnel from the water, basic first aid artificial respiration, and correct radio procedures. At least one of the members of the Watermanship and Safety

## Chapter 3. Boats And Motors

RECONNAISSANCE AND
ASSAULT BOATS
Three-Man Reconnaissance Boat The three-man reconnaissance boat is designed to carry a three-man crew, together with individual equipment, on reconnaissance missions. The boat is fabricated of neoprenecoated nylon cloth and consists primarily of a main flotation tube, divided into four separate compartments, and a single layer floor which forms a separate air chamber. The boat is equipped with two oarlocks, three paddles, a
600-pound capacity towing rope, repair kit, hand pump, backpack, and a rope lifeline running around its perimeter.

Inflation The boat is inflated by using the hand pump made possible by means of the two oarlocks atand adapter, provided in the boat's carrying tached to the flotation tube. When the boat is case. The boat should be inflated to apoperated by one individual, the maximum speed proximately 2 pounds per square inch (psi).

through still water is approximately 4 FPS.

There are five inflation valves, each inflating a When the boat is fully loaded with two people separate compartment on the boat. Inflation paddling and one person tilling (steering), the time is approximately 5 minutes.

boat's maximum speed is approximately 3.5 FPS
in still water.

Propulsion The boat is hand paddled and there are no Transportation provisions for the attachment of an outboard The boat is normally carried in its backpack by motor. One-person operation of the boat is one person.

Mission The types of missions which can be accomplished with the three-man reconnaissance boat include measurement of stream width and depth, determination of river bottom conditions, and inspection of bank conditions to determine suitable crossing sites. The boat may also be used for general utility work in bridge construction and for infiltration of small groups of personnel into enemy territory.

Crossing capability The three-man reconnaissance boat is designed to operate in rivers with currents not exceeding 4 FPS. The boat can carry three personnel (with equipment) or a total of 675 pounds.

Seven-Man C02 Inflatable Landing Boat The seven-man landing boat is designed to carry seven people in an assault across a water obstacle. The boat is constructed of neoprenecoated nylon cloth and can be inflated using the C02 cylinder provided, or by use of a foot or hand operated pump (also provided with the boat). In addition to the C02 cylinders and pumps, the boat comes equipped with a carrying case, six paddles, an anchor, an emergency repair kit, and a motor mount. An outboard motor is NOT automatically provided with the boat.

Mission cated from neoprene-coated nylon fabric. It is The primary mission of the fifteen-man assault divided into 10 separate air compartments. The boat is to carry assault troops across rivers or main flotation tube, itself, is divided into six other bodies of water. This boat can also be separate compartments, any three of which can used for reconnaissance missions such as for be punctured and still enable the boat to carry a the inspection of river bottoms or bank condifull load. This assault boat comes equipped with tions prior to river crossing operations.

11 paddles, 3 pumps, a repair kit, towing bridle, lifeline, transom for mounting a 25-or 40-horse-
Crossing capabilities power outboard motor, and carrying case. An This pneumatic assault boat is designed to outboard motor is NOT automatically provided carry 15 combat equipped soldiers or apwith the boat.

proximately 3,375 pounds of equipment.

When the boat is paddled by hand, the crew will Mission The primary purpose of the seven-man landing boat is to carry assault troops and equipment across rivers or other bodies of water. The boat can be used in general bridge construction or in the reconnaissance of rivers prior to crossing operations.

Crossing capability When paddled by hand, the boat can carry up to seven people or approximately 1,575 pounds in a river current not exceeding 5 FPS. When outboard motors are used, this same load can be carried in currents up to 10 FPS.

Inflation The seven-man landing boat is inflated instantly by pulling the cord attached to the C02
cylinder. If additional pressure is needed, the small hand or foot pump can be used to apply air to the uninflated section(s).

Fifteen-Man Inflatable Assault Boat The fifteen-man inflatable assault boat, also known as the pneumatic assault boat, is fabrififteen-man assault boat can negotiate currents not exceeding 10 FPS.

normally consist of 3 engineers and 12 insion, the crew will normally consist of 2 infantrymen. The boat will handle this load in curgineers with a full complement of infantrymen.

rents not exceeding 5 FPS. When a 25- or 40-
When under the power of outboard motors, the horsepower outboard motor is used for propul-
Inflation The fifteen-man assault boat can be inflated using the pumps provided with the boat in 5 to
10 minutes.

Propulsion The fifteen-man inflatable assault boat can be paddled or propelled by outboard motors. Although the motor mount for the outboard motor is provided with the boat. the outboard motor is NOT automatically provided with the assault boat.

Transportation The fifteen-man assault boat is normally transported on standard military cargo trucks. One 2 l/2-ton truck can carry 20 deflated assault boats.

Allocation of Reconnaissance Assault Boats Reconnaissance and assault boats are provided to engineer units as shown in Table 5.

formation, consult *TM 5-1940-277-10.* A newer version of the BEB-SD, the USCSBMK-2, is currently being provided to float bridge companies. Modifications on this boat include the provision of an internal cooling system, reinforced pushing knees, as well as other minor changes. The operating characteristics and performance data for the MK-2 are the same as that for the original BEB-SD.

BRIDGE ERECTION BOATS
Bridge Erection Boat, Twin Jet, Aluminum Hull (USCSBMK-1) (BEB-SD)
The BEB USCSBMK-1 was originally purchased from Fairey Allday Marine Limited, United Kingdom, and is now the standard US
BEB. This boat is also commonly referred to as Launching and retrieving the BEB-SD
The BEB-SD is normally transported using the modified M812 series, 5-ton bridge transporter.

This transporter is fitted with a cradle which allows the operator to launch or retrieve the boat in the same manner as the ribbon bridge bays.

the "bridge erection boat, shallow draft" or BEB-SD. The primary purpose of the BEB-SD is to support the construction of floating bridges, as well as the construction and propulsion of military floating rafts. The boat may also be used as a general work boat in support of diving operations and maritime projects, for inland water patrols, and as a safety boat for river crossing operations. The BEB-SD can be used as an assault boat in circumstances where the need to quickly cross the assault forces outweighs the possibility that the boat will be damaged or destroyed. In making this decision, the commander must realize that the loss of even a few BEBs can seriously jeopardize the success of rafting operations. For additional into the aircraft by means of an airlift sling provided in the Ribbon Bridge Supplemental Set. See Appendix B for additional information regarding airlift procedures.

position of these scoops is mechanically adjusted by the steering wheel and the scoop control levers mounted on the boat's control panel.

The steering wheel controls the port-starboard directional movements while the scoops control the forward-reverse motion. At low speeds the scoops can also be used to turn the boat by having one scoop in REVERSE position and the other in a NEUTRAL or FORWARD position.

Operation The BEB-SD is normally operated by a crew of two licensed boat operators. The boat is powered by two 212-horsepower, water-cooled, six-cylinder diesel engines. These engines each drive a hydrojet propulsion unit which provides the thrust to move and steer the boat. Water is drawn in through the grilles in the underside of the boat and expelled through nozzles mounted beyond the back of the boat. Movable shields or scoops are mounted over these nozzles to direct the flow of water from the propulsion units. The The site boat should be launched or retrieved at a having a uniform bank and a streambed slope of 11 degrees or less. The site should also have a water depth of 48 inches or more at and beyond the launch point. The two methods of launching the boat from the transporter are the calm water launch and the fast water launch.

The calm water launch is normally performed in currents of not more than 5 FPS. The fast water launch can be conducted in currents of 5 to 10
FPS. Boats may be retrieved under similar bank conditions, but current velocities should not exceed 5 FPS. Further guidance for the launch or retrieval of the BEB-SD is provided in *TM 5-1940-277-10.* The BEB-SD can also be transported using medium or heavy lift helicopters. When helicopters are used, attach the boat Bridge Erection Boat, 27-Foot Some Army National Guard and Army Reserve units currently maintain the 27-foot BEB. This boat is a gasoline-powered, twinscrew BEB. It should be noted that most of these boats have been modified to use diesel trailer which is towed by a 2 l/2-ton truck. The stem section is carried in the truck bed. During transport, each section rests on a special full-fitting cradle, to prevent damage to the boat. Upon arrival at the launch site, the boat can be launched from the truck and trailer by using a crane or some other lifting device. The boat's two-person crew can then couple the bow and stem sections. It is also possible to couple the two sections and launch the entire boat using a crane.

fuel rather than gasoline. The 27-foot BEB is constructed of a two-sectioned, aluminum hull, consisting of a bow cargo-carrying section and a stern section which contains the engines and operator's cockpit. The two sections are quickly and easily connected by means of special connecting hooks and clamps, and are just as easily disengaged.

This boat was designed with the primary purpose of propelling M4T6 and Class 60 rafts and to aid in the construction of heavy floating bridges.

Launching the 27-foot BEB
The 27-foot BEB can be transported in several manners. Units equipped with the modified M812 5-ton bridge truck can transport and launch the 27-foot BEB using the same method that is used to launch the BEB-SD.

Those units not equipped with the modified M812 bridge transporter can transport the boat in two sections. The bow section is carried on a standard 4-ton bolster trailer or a 2 1/2-ton pole STANDARD MILITARY OUTBOARD
MOTORS
Use The primary function of military outboard motors is to propel inflatable assault boats.

Outboard motors may also be used to push LTRs and other small items of floating equipment. When considering whether or not to use outboard motors when conducting an assault across a river, the commander should weigh the advantages and disadvantages offered by the outboard motor. Obviously, the motor can provide the commander a quicker assault crossing than would be obtained by directing that the soldiers paddle their assault boats. The use of outboard motors also enables the use of assault boats in currents up to 10 FPS. (Paddled assault boats can only be used in currents up to 5 FPS.)
On the other hand, the noise produced when using outboard motors can compromise the commander's ability to achieve some degree of surprise as to when and where the assault is being conducted.

Operation The 27-foot BEB is powered by two separately controlled, six-cylinder marine type engines mounted side by side in the stern section of the boat. Each of these engines drives a propeller.

The drive of both engines is equipped with forward, neutral, and reverse gears. The engine speed control (throttle) and transmission control are located on the same lever and both rudders are operated simultaneously by turning the steering wheel.

Types The US Army currently relies primarily upon
40-horsepower outboard motors to propel assault boats or LTRs. At this time, there is no standard 40-horsepower motor. Various models of Johnson, Evinrude, Mercury, and Outboard Marine Corporation (OMC) motors are available. Operators should refer to the references provided by the makers of their particular make or model of outboard motor for information on operation and maintenance.

## Chapter 4. Improved Float Bridge (Ribbon)

Bridge Transporter The standard bridge transporter is a modified rear of the truck cab. An 11,000-pound capacity US Army M812 5-ton truck chassis which winch works in conjunction with the boom to provides a self-contained unit for transporting, provide loading and unloading capabilities. Belaunching, and retrieving the bridge bays.

cause of the weight of the bridge bays, extreme Modifications of the truck chassis include the caution should be exercised by vehicle addition of three bay supports with associated operators during overland transportation to rollers, restraint locks, vertical tie-down locks, prevent damage to the truck's suspension sysbay support stops, two steel grating walkways, tem. The modified M812 bridge transporter is a and a hydraulically operated boom. The Military Load Class (MLC) 17 vehicle when operator's control stand is located to the left transporting a bridge bay. A 10-ton cargo pallet The ribbon bridge is a floating, modular asset with an integral superstructure and floating supports. Individual bays are joined to form rafts or bridges in support of river crossing operations. Ribbon bridges and rafts provide the maneuver commander with a reliable and responsive means to cross wet gap obstacles from the march. Ribbon equipment was actually reverse engineered at the United States Army Mobility Equipment Research and Development Command (MERADCOM) at Fort Belvoir, Virginia from photographs and drawings of the Soviet PMP Bridge. The ribbon bridge system was type classified in June 1972, and is currently the United States Army's primary assault floating bridge. For additional information, consult TM 5-5420-209-12.

COMPONENTS
The ribbon bridge system consists of three major components:
 Bridge transporters Interior bays Ramp bays Although BEBs are not a component of the ribbon bridge system, boats are required for the propulsion of ribbon rafts, as well as for the assembly and anchorage of ribbon rafts and bridges.

may be allocated to each transporter for hauling materiel. The M812 can also transport all US
Army BEBs when fitted with a special cradle.

Interior Bay The interior bay is the primary load carrying component of a ribbon bridge or raft. Each interior bridge bay is a four-ponton, folding module consisting of two roadway pontons and two bow pontons. The interior roadway pontons are joined to each other and to the adjacent bow pontons by hinges and pins along their adjacent edges. The roadway is welded to the roadway pontons, thus eliminating the need for separate intermediate pneumatic supports. One interior bay provides a roadway that is approximately 13.4 feet wide (13 feet 5 inches).

The two bow pontons aid in flotation and provide walkways for personnel on both sides of the roadway.

Ramp Bay The ramp bay is similar in construction to the interior bay, except that the bay's shore end is tapered. Ramps are always attached to both ends of a ribbon raft or bridge. A hydraulic system located within the ramp bay permits the ramp to be raised to accommodate bank heights of up to 42 inches. Two 7-foot extensions which serve as approach ramps are hinged to the roadway ponton on the shore side of the ramp to allow for ease of loading and unloading vehicles from bridges or rafts.

ALLOCATION OF RIBBON EQUIPMENT
The ribbon equipment is currently authorized in all Divisional Bridge Companies and all active duty Corps Assault Float Bridge Companies. The J-series Table of Organization and

## Water Depth (Draft) Restrictions Water Depth Restrictions Are Shown Below.

Equipment (TOE) allocates ribbon equipment as shown in Table 6.

EQUIPMENT
RESTRICTION

equipment or injuring personnel. Other selection criteria include the height of the banks, the bank slopes, and the depth of the water at the site. There are four methods of launching ribbon equipment:

Free launch
Ribbon raft
24"
(fully loaded)
Ribbon bridge
24"
Controlled launch
BEB-SD
22"
High bank launch
27-foot BEB
40"

Helicopter delivery These launches and their applicable site restrictions are discussed under Ribbon Launches on page 22.

CONSIDERATIONS FOR THE TACTICAL
EMPLOYMENT OF RIBBON EQUIPMENT
Ribbon equipment is designed for use, primarily, during the rafting and bridging phases of the deliberate river crossing. Because ribbon bridges and rafts are significantly faster to construct with fewer personnel than other floating bridges, they are heavily relied upon in this capacity. Site considerations are of primary importance when ribbon equipment is to be used for rafting or bridging operations. Both the launch sites and actual bridge or raft sites should be considered.

Raft and Bridge Sites The tactical plan plays a major role in the selection process. The considerations discussed in Chapter 1 are critical to the selection of these sites. Some additional factors which apply to ribbon equipment are as follows:
Bank restrictions The ribbon ramp bay can articulate a maximum of 20 degrees from its horizontal position. This means that the maximum allowable bank height for the loading or unloading of ribbon rafts or bridges is approximately 3.5 feet. The shore leading to the raft or bridge ramp should be gently sloping (no more than a 20 percent slope), generally free of rocks or other debris, and firm.

Launch Sites Site selection depends upon several factors.

Generally, ribbon equipment is launched downstream from bridge or rafting sites to allow for ease of construction and to prevent runaway bridge bays from damaging other Current velocity The velocity of the river's current can impact significantly upon all float bridging operations. Ribbon equipment can be used in currents of O
to 10 FPS. Rafting and bridging operations can become quite difficult in currents greater than 5
FPS unless the boat operators and bridge crewmen have experience working in swift currents. For raft sites on rivers with currents greater than 5 FPS, the unloading site on the far shore should be located downstream of the loading site on the near shore to allow for downstream drift. Some recommended site layouts are shown on pages 32, 33 and 34.

GENERAL CONSTRUCTION
Ribbon Launches As discussed earlier, there are four methods of launching bridge bays. Table 7 provides the launch site restrictions for these launches.

These restrictions are discussed further in the following paragraphs. *TM 5-5420-209-12* lists the actual steps performed when conducting a free, controlled, or high bank launch.

Free The free launch method is the preferred means of launching ribbon equipment from the M812 bridge transporter. This method allows the bay to roll off the truck and unfold upon entering the water. When adequate preparation is performed in the engineer equipment park, this launch is the fastest method, requiring only a few seconds once the truck backs up to the edge of the water. Ribbon bays can be launched from banks up to 5 feet high with slopes up to
30 percent. The free launch of an interior bay requires a minimum of at least 36 inches of water, while a ramp bay requires at least 44 inches of water. These depths apply when the truck is backed into the water (no bank height)
and when bank slopes are 10 percent or less.

When free launching a ribbon bay from a bank height of 5 feet and a slope of 30 percent, approximately 72 inches of water is needed.

Controlled The controlled launch of ribbon bridge bays is recommended when water depth is limited or when shortage of BEBs may exist. When conducting a controlled launch, the transporter operator backs the truck into the water and winches the bay slowly into the water. The bay is allowed to unfold at the operator's discretion.

BEB is required to secure the bay once it is in the water. The boat operator allows the bay to unfold by opening the downstream travel latch.

Deployment by helicopter Ribbon bridge bays and BEBs are helicopter transportable. Medium and heavy lift helicopters can be used by the tactical commander to fly rafting and bridging equipment to the crossing sites. Interior bays can be flown at air speeds of up to 80 knots, but must have a drogue parachute attached when flying at speeds greater than 40 knots, to prevent the bay from spinning. Ramp bays can be flown at air speeds of up to 100 knots. Like the high bank launch, a BEB is needed to secure the bay and allow it to unfold. At least 30 inches of water is recommended for such a site. Appendix B provides additional information concerning airlift operations.

The recommended depth of water at trolled launch site is 30 inches. This the conmethod however, can be used in only 17 inches of water when extreme care is used. (A ribbon bay requires 17 inches of water to unfold.) It is also important to note that the BEB-SD must have
22 inches  of water available if it is to be used to maneuver the bay. A controlled launch is normally conducted on banks with a gradual slope
(0 to 20 percent) and with no bank height since the truck must back into the water to launch its bay. Execution of the controlled launch normally requires approximately 10 minutes.

High bank The high bank launch must be used when the bank height at the launch site is between 5 and
28 feet. This method is normally used only when a more desirable site is unavailable. This process has two distinct phases:
The **first phase** is the off-loading of the bay onto the ground. The transporter is maneuvered parallel to the bank and the bay is lowered onto the ground. Cribbing is used to prevent damage to the bay.

The **second phase** of the launch requires the transporter to be backed perpendicular to the bay. Chains are attached to the four lift points on the bay and the transporter cable is run through the snatch block and attached to the truck's boom. The boom can then be used to lift the bay off the ground and place the bay in the water. If the bank is not completely level, some means of restraining the front end of the truck should be used to prevent the truck from overturning. Thirty inches of water is desired for the high bank launch although the launch can be carefully conducted in 17 inches of water. A
Securing Bridge Bays The securing of bridge bays must be completed as quickly as possible so that the bays may be moved from the launching area to the actual raft or bridge site. After the bridge bay has been launched and unfolded, a BEB will approach from the downstream direction. The front pushing knees of the boat are placed against the downstream bow and centered on the bay. The assistant boat operator secures one bowline (at least 3/4 inch in diameter) to each of the anchoring pins on the downstream bow ponton of the ribbon bay. The assistant will then pull each line tight and secure it to the bow bollard on its respective side of the boat. In currents greater than 5 FPS, the bowlines may be attached to the bay cleats. Steering lines can then be attached from the stern bollard to the anchoring pin on the bay. In currents of 5 FPS or less, the steering lines may be omitted. After the bridge bay is connected to the boat, the bridge crew secures the bay as follows:
1. Engage the roadway/roadway ponton upper connectors (dogbones) on the bay. It may be necessary to use the roadway ponton connector tool when engaging the roadway/roadway upper connectors on the ramp bay.

2. Check to ensure that the lower lock drive screw turns freely and the connecting pins are fully retracted.

3. Engage the four roadway/bow ponton bridge latches. The backs of the latches are painted yellow to allow for a visual check on engagement.

them between the top of the bow walkway of one bay and the bottom of the roadway of the other bay.

Note. The top of the lower lock drive pin is 3/4
inch below the deck when lower lock drive is fully engaged.

5. Disconnect the boat if it is not needed for bridge anchorage or raft propulsion.

bay/bridge bay upper connectors.
4. The bridge centerline crew secures the lower
lock drive pins by turning the T-bar
connecting wrench in the clockwise direction. If connection is difficult, the
bridge boat can apply power in forward and
reverse to adjust the bay's position.
Wrecking bars may also be used to apply an
up and down force to the joint by inserting
Interior Bay to Interior Bay Connections
1. The boat with the interior bay connected
approaches the stationary interior bay from
the downstream side.
2. When the bays are as close as possible, the
bridge centerline crew tosses the tag lines to
the boat crew which connects the lines to the
bay rope cleats. The bays are then pulled
together. Boat hooks may also be used.
3. The securing crew engages the bridge
turning the T-bar wrench in the clockwise direction. If the connection is difficult, the ramp pumps may be pumped to raise the connector yoke while force is applied to the T-bar.

Note. The top of the lower lock drive pins are approximately 3/4 inch below the deck when the pin is fully engaged.

6. Disconnect the boat if it is not needed for anchorage.

Ramp to Interior Bay Connections
1. The boat which secured the ramp bay
approaches two or more connected and
anchored interior bays from the downstream side.
2. When the ramp bay has been brought as
close as possible to the interior bays, the
bridge crew secures it using tag lines and
boat hooks. The crew next attaches the ramp
connection tool hooks to the
roadway/ponton upper connectors of the adjacent interior bay and the ramp bay.
3. The bridge centerline crew aboard the
interior bay raises the ramp bay, using the 60-inch wrecking bar. This is done by
inserting the bar into the holes in the ramp
bay bow hinge blocks using the interior bay
roadway as a pivot point, and applying a downward force to the top end of the bar.
4. As force is applied to the wrecking bars, the
bays are pulled together by ratcheting the
ramp bay connection tool. As soon as the
bays are together, engage the bridge
bay/bridge bay upper connectors.
5. The lower lock drive pins are then driven by
RIBBON RAFTING OPERATIONS
Raft Design Criteria Ribbon rafts may be used during both the hasty and deliberate river crossing to project combat firepower across a water obstacle as rapidly as possible. The type of raft to be constructed depends upon the MLC of the equipment to be rafted, the length of the vehicles, and the current velocity of the river. As a general rule, the number of armored tracked vehicles that can be placed on a ribbon raft will be limited by the load classification of that raft, whereas the number of wheeled vehicles that can be placed on a raft will be limited by the length (load space) of the raft. Table 8 provides the means for designing ribbon rafts, to include a determination of assembly time, load space, rafting method, number of boats required for raft propulsion, and classification for all types of ribbon rafts.

This raft, therefore, provides the greatest flexibility to the maneuver commander.

Assembly Times for Rafts Table 8 provides the assembly time for each type of ribbon raft. The assembly times provided are based upon construction by a trained bridge section during ideal, daylight conditions. Assembly times will increase by 50
percent for construction at night.

EXAMPLE: What is the planned assembly time for a six-bay ribbon raft to be constructed at night?

SOLUTION: Refer to Table 8. For a six-bay ribbon raft, the given assembly time is 20
minutes. This time represents the required assembly time for daylight construction, at night, add 50 percent. Therefore, the assembly time at night is 20 minutes plus 10 minutes, or a total of 30 minutes.

Types of Ribbon Rafts Ribbon rafts can be constructed in a three-, four-, five-, or six-bay configuration. Tests are being conducted on the use of a seven-bay raft.

This information will be made available to commanders in the field upon completion of these tests. The type of raft needed is based upon the MLC required, the length (load space) needed, and the current velocity of the river. A threebay ribbon raft would consist of one ribbon interior bay and two ribbon ramp bays. This same principle applies for all ribbon rafts. Every ribbon raft will have two ramp bays and either one, two, three, or four interior bays. For example, a six-bay raft would be constructed of four ribbon interior bays and two ramp bays. The six-bay raft provides the greatest MLC and load space.

raft's roadway (one on each side of the raft).

current velocity. A three-bay raft always re-
The longitudinal method should not be used quires two boats for propulsion. When propellwhen the current velocities in the loading or uning a four-, five-, or six-bay ribbon raft, two loading areas exceed 5 FPS. In these instances, boats can be used in currents of O to 5 FPS.

conventional rafting should be used.

Three boats must be used when these rafts are Conventional. When rafting conventionally, propelled in currents greater than 5 FPS.

the BEBs are tied off perpendicular to the raft EXAMPLE: Given a raft site with a current and on the downstream side. The number of velocity of 8 FPS in the main channel and 6 FPS
boats required when rafting conventionally in the loading area, what method of rafting will depends upon the type of raft and the river's be used and how many boats are required to Load Space of Ribbon Rafts Table 8 provides the load space for each type of ribbon raft. Each ribbon interior bay provides 22 feet of effective load space and a roadway width of approximately 13.5 feet.

Ramp bays are not loaded and, therefore, not considered when determining available load space. Similarly, the bow pontons are designed as walkways on either side of the roadway and are not loaded.

EXAMPLE: What is the planned load space of a six-bay ribbon raft?

SOLUTION: Refer to Table 8. Load space for a six-bay ribbon raft is given as 88 feet. The roadway width is 13 feet 5 inches.

Classification of Ribbon Rafts The determination of the MLC of a ribbon raft is based upon the river's current velocity and the method of rafting. The current velocity is determined by conducting a reconnaissance at the proposed rafting site. The process for selecting the method of rafting is described below.

Methods of rafting As discussed in Chapter 2, the two methods of rafting ribbon equipment are conventional and longitudinal rafting. Each method has its advantages and disadvantages. The selection of either depends upon the current velocity, the number of BEBs available, and the MLC of the vehicles to be crossed.

Longitudinal. This method is generally the preferred method of rafting heavy equipment.

The longitudinal method typically provides a higher raft classification. When rafting longitudinally, two BEBs are tied off parallel to the Ribbon Raft Construction Construction of ribbon rafts is generally accomplished in four steps:
1. Launching bays
2. Securing bays
3. Connecting bays 4. Securing the raft Procedures for the launching, securing, and connecting of bays, are discussed in this chapter under General Construction. Raft construction and the securing of rafts to boats are discussed in the following paragraphs.

propel a six-bay ribbon raft? What is the classification of this raft?

SOLUTION: Given a current velocity greater than 5 FPS in the loading area, CONVEN-
TIONAL rafting should be used. Since the highest current velocity expected is 8 FPS and a six-bay ribbon raft is used three boats are required for conventional rafting. Next, refer to Table 8. Given a six-bay ribbon raft, rafting conventionally in a current of 8 FPS, the MLC of the raft is Class 55 for both wheeled and tracked vehicles.

Note. The asterisk by this classification reaffirms the fact that three boats are required for propulsion of this raft.

Raft assembly
Rafts are generally assembled as follows:
1. Launch all boats required to construct and
propel the raft.
2. Launch a ribbon interior bay. Secure the bay
and move it upstream to the construction site
(when applicable).
3. Launch all other interior bays as required for
the type or size of the raft to be built. Secure these bays and move them upstream to the assembly area.
4. Check all bays prior to connection to ensure
that the lower lockpin is in the OPEN
position, the roadway/bow ponton bridge latches are engaged, and the
roadway/roadway ponton travel latch is
rotated down.
5. Connect all interior bays.
6. Launch the first ramp bay and attach it to the
raft on the near shore end of the raft.
7. Launch and attach the second ramp bay.
8. Tie off the boats to the raft.
Securing rafts The manner in which boats are tied off to ribbon rafts depends upon the method of rafting that is selected. Refer to *TM 5-5420209-12* and
7345-1940-277-10 for additional guidance.

RIBBON BRIDGING OPERATIONS
Design of Ribbon Bridges Ribbon bridges will initially be the primary crossing means during the bridging phase of a deliberate river crossing. When designing ribbon bridges, the quantity of ribbon equipment needed, the required assembly time, and the classification of the bridge are major considerations.

Determination of Equipment Requirements The number of ribbon interior bays needed to bridge a given gap can be determined using the formula:
SOLUTION: Number of interior bays SOLUTION: Divide the required length of bridge by the assembly time (day) and then add
50 percent for night construction.

Round up to 21 interior bays.

500 eet o f f bridge = .833 hours (day)
600 feet per hour Assembly Time for Ribbon Bridges
.833 hours (day) x 1.5 = 1.25 hours (night)
Ribbon bridges can be emplaced during So it would take 1.25 hours or 1 hour and 15
daylight hours at the rate of 600 feet per hour or minutes.

200 meters per hour. Assembly times should be increased by 50 percent when construction is at Classification of Ribbon Bridges night. These times are also based upon the use The classification of a ribbon bridge is based of art experienced bridge crew for bridge conupon the current velocity at the bridge site.

struction under ideal conditions.

Table 9 gives bridge classifications for different EXAMPLE: How much time is required to current velocities.

construct a 500-foot ribbon bridge at night?

Additionally, two ramps are required for every ribbon bridge (one at each end of the bridge).

EXAMPLE: How many ribbon interior bays are needed to bridge a gap across a 500-foot river?

EXAMPLE: What is the classification of a
500-foot ribbon bridge in a river with a current velocity of 7 FPS? Assume that a normal crossing will be conducted.

SOLUTION: Read Table 9. The length of the bridge has no impact upon the bridge's classification. Reading across the table, for a normal crossing a ribbon bridge constructed on a river with a current velocity of 7 FPS will be capable of crossing wheeled vehicles with an MLC of 82 (or less) and tracked vehicles with an MLC of 70 (or less).

Swinging bridge method The purpose of the swinging bridge method is to allow connection of the bays to be made along or near the shore, where the current will be considerably slower than in the main channel. This makes bay-to-bay connections easier.

Once the connections are made, the bridge is swung into place using BEBs. An additional limitation is that the exact length of the bridge must be known to successfully use this assembly method. Note that the bridge must always be swung upstream, against the river's current. Assembly using this method is normally accomplished as follows:
1. Launch the required number of BEBs.

successive bay techniques. River conditions such as the current velocity and the existence of obstacles are the major considerations in the selection of either bridging method. The swinging bridge method is normally the fastest of the two procedures. It is recommended that this method be used only when currents are 5 FPS
or less and when site conditions are nearly ideal
(minimal debris in the water and no obstacles in the river). The successive bay method is therefore recommended in rivers with fast currents
(greater than 5 FPS) and in situations where debris in the water is prevalent, or when obstacles such as sandbars or islands exist in the vicinity of the construction site.

Construction of Ribbon Bridges The two textbook methods of constructing ribbon bridges are the swinging bridge and the the bridge bay/bridge bay upper connectors to the UNLATCHED position, except for those connecting ramp bays to interior bays.

2. Launch two interior bays. Secure these bays
using two of the BEBs that were launched earlier.
3. Move the bays to the assembly area just
below the bridge centerline and connect
them.
4. Launch one ramp bay, secure it with a BEB
and move the bay to the assembly area.
5. Connect the ramp bay to the interior bays
forming the near shore end section.
6. Anchor the near shore end section to the
shore temporarily. A bridge transporter may
be used as temporary anchorage.
7. Once the ramp bay has been moved from the
launch area, proceed to launch and connect
the bays needed to complete the bridge. Hold the assembled bridge with BEBs as
required.
8. After the connection of the final ramp bay,
articulate the far shore ramp. This is done by
setting the pump valve lever on the PUMP
position, opening the reservoir vent valve
and pumping to the desired elevation.
9. Swing the bridge until sufficient room is
available to maneuver additional BEBs to the downstream side of the bridge. Swinging
of the bridge can be started by attaching a
boat to the end ramp bay and towing the bridge until additional boats can be
connected.
10. Completely swing the bridge into position
and adjust the anchorages as needed.
11. Lower the ramps for grounding and position
the bridge transporters for end span
anchorage.
12. Set the ramp pump valve levers to the
TRAFFIC position and close the reservoir
vent valves. Raise the handrails and move
the vicinity of the construction site. The construction of a ribbon bridge using this method is normally accomplished as follows:
1. Launch the required number of BEBs.
2. Launch two interior bays. Secure these bays
using two of the BEBs that were launched earlier.
3. Move the bays to the assembly area located
at the far shore end of the bridge centerline
and connect them.
Successive bay method The assembly of a ribbon bridge by successive bays is accomplished by the consecutive addition of bays along the bridge centerline. This method is normally used in fast currents or when a number of river obstacles are present in

enough to allow the ramp bay to ground. The
bay is pulled shoreward, the approach guys
tightened and the ramps lowered.
Articulation of the ramp is accomplished by
opening the reservoir vent valve, setting the pump valve lever in the PUMP position, and
pumping.
As soon as the first ramp and interior bays
7.
construction of the near shore end span.
8. Move the bays to the near shore bridge
centerline and connect them. The near shore
anchorage crew provides temporary anchorage, articulates the ramp, and with the use of a transporter pulls the bays shoreward to allow enough room for bridge
closure.
are launched and moved from the launching
9. Launch the interior bays needed to complete
area, repeat steps 2 through 4 for
the bridge. Move the bays to the far shore
4. Launch one ramp bay, secure it with a BEB
and move the bay to the assembly area at the
far shore.
5. Connect the ramp bay to the interior bays
forming the far shore end section.
6. Anchor the far shore end section to the
shore temporarily using approach guys attached to deadmen or some other form of
holdfast. To accomplish this, the bridge
centerline crew articulates the ramp bay
bridge centerline and connect the bays
working from the far shore to the near shore.
10. After each connection, the BEBs not needed
for bridge anchorage will return to the launch area to secure another interior bay
until all bays have been secured.
11. When closing the bridge, the last interior bay
will be moved into place and connected to
the far shore centerline first. The near shore
end span will then be pushed offshore by
either the transporter rear winch and boom or manually until the final connection is
made. The ramp must be articulated to allow
for this offshore movement.
12. Set the ramp pump valve levers to the
TRAFFIC position and close the reservoir
vent valves. Raise the handrails and move
the bridge bay/bridge bay upper connectors to the UNLATCHED position, except for those connecting ramp bays to interior bays.
sections are installed it is possible to continue to add ribbon interior bays to both end sections, working towards the middle. After construction is finished, BEBs help maneuver the bridge sections together.

complished by tying BEBs to the downstream side of the bridge. The number of boats required depends primarily upon the river's current velocity as shown in Table 10.

When using BEBs as a system of a temporary anchorage, boats should be checked for fuel consumption at least every 2 hours and refueled as necessary. Standby boats should be available to replace disabled boats. Refer to Table 11 for planning figures for the consumption of fuel by boats.

Anchorage of Ribbon Bridges Because ribbon bridges are used primarily as assault bridges, the anchorage systems for these bridges are generally temporary in nature. Normally, anchorage of ribbon bridges is ac-
Alternative methods of bridge construction In many cases, the textbook methods for constructing ribbon bridges may be infeasible or unacceptable. In these circumstances, the bridge officer in charge (OIC) and the noncommissioned officer in charge (NCOIC) must decide upon an original or expedient method of construction. It may be desirable, for example, to modify the swinging bridge method. This can be accomplished by building along both the near and far shore, and swinging the bridge closed against the current. This method prevents the need for an exact measurement along the bridge centerline, since a bay may be added or removed prior to closure. The successive bay method of construction may also be modified. Once the near and far shore ramp

## Improved Float Bridge (Ribbon)

In addition to the BEBs used to hold the bridge against the river's current, approach guys must be installed in accordance with
(IAW) Chapter 8. Approach guys prevent the bridge from creeping  away from the shore as a result of the impact of vehicles driving onto the bridge's ramps. If it is determined that the bridge will need to be in position for a long period of time, more permanent systems of anchorage should be considered (see Chapter
8).

OPERATIONAL MAINTENANCE
Operators and bridge crewman should refer to TM 5-5420-209-12 when performing preventive maintenance checks and operator level services on any of the components of the ribbon equipment system.

Inspections Preventive maintenance and frequent inspections of ribbon rafts and bridges, while they are in use, is an essential step in ensuring that the bridge is capable of performing its required mission. During a rafting operation, the raft commander is responsible for ensuring that these checks are made. In bridging operations, a maintenance crew, under the supervision of a noncommissioned officer (NCO), is normally assigned to the bridge. Some inspections which should be performed include--
Leakage At least once every 3 hours during heavy traffic periods, the pontons should be inspected for leakage. If a significant amount of water is found, it should be pumped out using the bilge pump.

Debris Do not allow debris to build up against the upstream bow. Most debris should pass completely beneath the bridge, depending upon the size of the debris and the nature of the river's current.

Shore erosion When bridges are subjected to heavy use, the wave action at each ramp may cause the shore to wash out. The end span anchorage system must be taut to keep the bridge movement to a minimum. If the erosion continues, the ramps should be raised and sandbags or other suitable fill material should be placed under the ramp roadways. This condition can often be eliminated by adding an interior bay and pulling the ramps further onto the shore.

Ramp cylinder controls Prior to allowing vehicle traffic on the bridge, the NCOIC must check the ramp cylinder controls. The ramp cylinder pump valve lever will be placed in the TRAFFIC position. This will allow the ramp bay to automatically adjust to any rise in the water level. To compensate for falling water level, the pump valve must be placed in the PUMP position and pumped until the ramp bay reaches the lower water level. Once the ramp has been repositioned, place the lever in the TRAFFIC position before allowing additional traffic on the bridge.

Roadway During periods of heavy traffic, debris such as mud, dirt, and rocks may be deposited on the bridge or raft roadway surface. Wash down the roadway surface with the bilge pump at frequent intervals (as permitted by the tactical situation and the need for operation of the bridge or raft).

state of the art means of conducting military river crossing operations.

COMPONENTS
The major components of one set of M4T6
are
bow ends, are upswept 40 degrees and covered with laced skirts. The skirts prevent debris from lodging between the tubes, improve the hydraulic characteristics of the float, and protect the tubes from puncture during launching.

Saddle Assembly The saddle assembly is placed upon the pneumatic float and bears the load of the bridge itself. The saddle assembly for a float includes eight interior saddle panels, two outrigger panels, and two saddle beams. Each saddle beam actually consists of five individual beams connected by double pinned joints. The weights Floats The pneumatic float which supports the M4T6 deck actually consists of two half-floats. Each half-float is 9 feet wide, 3 feet high, 22 feet long, and weighs 750 pounds. These half-floats are, in turn, made up of three tubes (called sausages) laced together side by side. These tubes are divided into four inflatable chambers, each fitted with a valve. The tapered noses, or The M4T6 floating bridges and rafts consist of a deck built of square, hollow aluminum sections (called balk) supported by pneumatic floats. The M4T6 equipment is hand erectable, air transportable, and can provide the crossing force commander with rafts and bridges capable of supporting MLC 70 traffic in river currents up to 8 FPS. The M4T6 was designed after World War II, combining the best characteristics of the older M4 and Class 60 bridges.

Proper military nomenclature for this set is the Bridge, Floating, Aluminum, Highway Type, Desk Balk Superstructure on Pneumatic Floats.

Until the advent of the ribbon equipment system in 1972, M4T6 equipment provided the and dimensions of these items are provided in the figure.

The two center beams rest on four saddle panels. At each end of the center beam, a shorter beam, called an end beam extends to the end of the level length of the float and rests on two saddle panels. Each end beam is extended by a lighter, inclined outrigger beam which rests on an inclined outrigger panel. The saddle beams are equipped with cleats (on the end beams) for securing the towing lines and with handles designed to receive the float straps. The center beam is also equipped with retainer lugs for receiving the saddle adapters.

Saddle Adapters The two types of saddle adapters are normal and offset. Their primary purpose is to provide a means to connect the deck balk superstructure to the saddle assembly, and to do this in such a way to provide sufficient work space between the two. Two like saddle adapters are used per bay of bridge (per pneumatic float). The saddle adapters are connected to the center saddle beams using the sliding retainer lugs located on these beams and their dimensions are given in the figure. In addition to providing work space between the saddle assembly and the balk, the offset saddle adapters permit floats to be placed closer together to allow for reinforced construction. To accomplish this, the beams which receive the balk-connecting stiffener have been shifted off-center approximately 14 inches.

Balk-Connecting Stiffener Balk-connecting stiffeners are secured to the saddle adapters and are designed to receive the bridge's deck balk. The stiffener has 26 recesses, each spaced 9.25 inches apart. These recesses receive the lugs on the bottom of the deck balk. Each piece of deck balk is secured to the stiffener with a steel pin. This pin is the same type used to connect the stiffener to the saddle adapters.

Deck Balk The three types of aluminum deck balk used in construction of M4T6 bridges and rafts are normal, short, and tapered balk.

Normal balk Normal balk is the primary component of the bridge's deck. Normal deck balk is 15 feet long,
9.25 inches in depth, and 8.5 inches wide. Normal balk weighs 225 pounds and is usually carried by four soldiers. Lugs on the lower side of the balk enable it to be pinned to the balk-connetting stiffener.

Short balk Short balk is designed to fill gaps in the normal balk pattern. These gaps occur
At the end of any five-float reinforced raft with a 16-foot 7-inch overhang.

At the end of any five-float normal raft with a 23-foot 4-inch overhang.

At both ends of any 23-foot 4-inch or 38- foot, 4-inch M4T6 fixed span. At one end of any 30- or 45-foot M4T6 fixed span.

Short balk are 8 feet 4 inches long and have the same cross section as normal balk. Each piece of short balk weighs 122 pounds and can be carried by two soldiers.

Tapered balk Tapered deck balk are used to create a sloping approach to the bridge deck and to fill gaps between the ends of normal balk. These gaps occur
At the end of any normal floating bridge that has a 21-foot 8-inch end span.

At the end of a four-float reinforced raft with a 21-foot 8-inch overhang. At both ends of any 21-foot 8-inch M4T6
freed span. At one end of any 30- or 45-foot M4T6 fixed span.

Tapered deck balk are 6 feet 8 inches long and have the same cross section and fittings as normal balk at one end. The other end is tapered and ends in a hinged plate. Each piece of tapered balk weighs about 100 pounds and can be carried by two soldiers.

Curb Adapters Steel curb adapters are used to raise normal deck balk 6 inches above the level of the roadway to provide curbing for a bridge or raft. These adapters are attached by pins to the balkconnecting stiffeners. Each adapter weighs about 15 pounds.

Ramps Four aluminum alloy raft ramps are used at each end of a raft to provide a sloping approach. Raft ramps are a little over 3 feet wide and have an effective length of 3 feet. They weigh 235 pounds and are normally carried by three soldiers. Each ramp is connected to the end of the raft by one horizontal pin and two vertical pins.

Abutment Plates Bearing plates Abutment bearing plates are 5 feet 9.75 inches long, 1 foot wide, 3.75 inches high, and weigh
165 pounds. This plate is fastened to the last balk-connecting stiffener on M4T6 bridges to distribute the load of the bridge on the shore.

Cover plates Aluminum alloy cover plates are used over joints in the deck and at abutments and trestles to protect balk handles from being damaged by vehicles crossing the bridge. Two short cover plates (1.5 feet long) and two long cover plates
(5.3 feet long) are required to cover the normal width of the bridge deck. The short cover plate weighs 28 pounds while the long plate weighs 97
pounds.

Trestle and Bracing Universal trestle The universal trestle consists of one transom, two columns, two shoes, and two chain hoists.

The top of the transom is fitted with recesses to accept 22 pieces of balk. The transom is pinned to each column. Each column has holes spaced every 6 inches to accommodate the transom. Three holes in the transom are spaced 9 inches apart to permit adjustments in transom height. These adjustments are made using chain hoists.

Trestle (strut) bracing Trestle bracing gives lateral and longitudinal stability to the trestles. The following trestle bracing equipment is issued with each trestle:
four strut braces, weighing 145 pounds each; eight bracing clamps, weighing 50 pounds each;
two wrenches, weighing 13 pounds each; and four holdfasts (with pickets), weighing 68 pounds each.

Other accessories Other accessories issued with the bridge include handrail posts (used on each side of the roadway), standard 100-pound kedge anchors, prefabricated holdfasts, a bicycle traveler for ferrying operations, an inflatable craft repair kit, and a bridge erection set.

ALLOCATION OF M4T6 EQUIPMENT
Currently, all active duty float bridge companies are equipped with ribbon float bridge equipment rather than M4T6. Some US Army Reserve and National Guard float bridge companies still maintain M4T6. Those companies which retain M4T6 are authorized five sets, providing about 700 feet of normal bridge or
540 feet of reinforced bridge. All other M4T6
equipment is maintained in depot stocks. One set of M4T6 can be used to construct any one of the following:
One 141-foot 8-inch normal bridge One 108-foot reinforced bridge One four-float normal raft One five-float normal raft One four-float reinforced and one five-float reinforced raft One six-float reinforced raft Three short fixed span bridges TRANSPORTATION AND LOADING OF
M4T6
The M4T6 can be carried on any standard military cargo truck or trailer having a rated capacity of 2 l/2 tons or more. Standard bridge trucks include the older M821(diesel) and M139 (gasoline) bridge trucks as well as the M812 bridge transporter. The M812 chasis has been modified to safely accommodate bridge loads in excess of 5 tons. Components of the set may also be airlifted using medium or heavy lift helicopters LAW Appendix B.

Normal Loading of M4T6 Equipment One set of M4T6 can be transported on 12
bridge trucks. Of these trucks, 5 trucks are used to carry normal bridge bay loads, 4 trucks carry offset bridge loads, 1 truck carries the trestle load, 1 truck transports the anchorage load, and
1 truck hauls the tools and rigging equipment.

More specifically, each truck is normally loaded as shown in Table 12a, b, c, and d.

CONSIDERATIONS FOR TACTICAL
EMPLOYMENT
Because of the considerable time and number of personnel required to construct M4T6 rafts and bridges, this equipment will probably not perform a major role in the rafting phase or even in the early stages of the bridging phase of a deliberate river crossing operation. The M4T6 rafts may be needed in situations where insufficient ribbon assets are available to swiftly cross the desired number of armored vehicles. Additionally, as the crossing force commander secures the bridgehead area and prepares to move forward, he will consider removing his ribbon bridges to deploy them with the advancing forces. These ribbon bridges must be replaced with more permanent bridges to sustain lines of communications. The M4T6
bridges, placed along MSRs, will normally serve in this capacity. The major consideration in determining the location of such a bridge is the existence of a well-defined road network leading both to and from the bridge site. Other considerations include the availability of adequate assembly sites, sufficient water depth, as well as the need for specialized equipment, such as air compressors, cranes, and BEBs. A discussion of these requirements is provided in this chapter.

GENERAL CONSTRUCTION
The M4T6 floats (bays) maybe constructed by hand at the bridge site, or they maybe partially preassembled in rear areas and then completed upon arrival at the launch site. When bays are preassembled, a crane or some comparable lifting device must be available to complete final assembly of the float. The two types of M4T6
bays are normal bays and offset bays. The difference between the two is determined by the type of saddle adapters attached to the bay's saddle assembly. Normal and offset bays are constructed in exactly the same manner.

pickets until the float is ready for launch.
4. The float is then inflated, working from the
stern to the bow. There are four
compartments in each of the three tubes
which make up each half-float. Each
compartment should be filled to a pressure of 2 psi, using a 250 cubic feet per minute
(CFM) air compressor.
5. Once the floats are inflated, the saddle
assembly crew can construct the remainder
of the substructure. The 10 saddle panels are placed on the top of the floats. These panels are placed so that the handles on the panels are in line with the tie-down straps on the outside of the floats. Do not tie the panels
Assembly and Launching of Floats by Hand
1. Two deflated half-floats are laid out stem to
stern. These half-floats are connected by
threading a connecting bar through the flaps on the bottom of each float, and buckling the
crisscross straps at the top of one half-float to the D-rings of the other. One-inch manila
rope may also be used in place of the connector bar.
2. Float rollers can be used to launch M4T6
bays when the bays are constructed by hand
and no crane or other lifting device is available. Each float roller is equipped with two air valves (one at each end). Float rollers
are placed beneath the uninflated M4T6
float prior to the construction of the
remainder of its substructure. The proper method of positioning the float rollers is to place the first float roller beneath the position where the first interior saddle panel will be placed. The additional float rollers
are then spaced evenly beneath the
remainder of the float.
3. Once the rollers are in position, the
retrieving lines are attached to each float
roller. One rope should be run through the
end of each roller and secured to D-handled
Assembly of floats by hand (continued)

1. Position saddle panels so that handles are in line with tie-down straps.
2. Place saddle beams on panels. Lock into place.
3. Place bow/stern connecting bar.
4. Place saddle adapters and balk-connecting stiffeners.
down until assembly of the substructure is
completed.
6. Next, the saddle beams are placed on top of
the panels. The two center beams are placed on the four center panels. These beams are
locked into place using the spring-actuated catches on the panels. The four end beams should be attached once the center beams
are in place. One end beam is attached to
the end of each center beam using two connecting pins. The end beams are placed
so that the tie-off cleat is located on the top of the beam. These beams are not attached
to the panels until the float is almost
completed. The last beams connected are the outrigger beams. These beams are
connected in the same manner as the end
beams.
7. Once the saddle beams are in place, the two
connecting bars are installed. Prior to
installing one connecting bar to each end of
the float, remove the guide pins from each of the outrigger beams. This will allow the
beam to be raised or lowered as needed without great difficulty. The connecting bars
should be threaded through the outrigger
beams and the holes provided in the skirt at
the bow end of the float. Pushup on the ends of the float to reinstall the guide pins. All panel should be attached to the saddle
beams at this time.
8. The saddle adapters are added next. The two
adapters rest on the top of the center beams. Each adapter is held in place by the sliding retainer lugs on the beam. A safety pin is placed on each retainer lug to prevent it
from accidentally disengaging from the
saddle adapter.
preassembled, although it is possible to completely preassemble floats and transport them to the river. In either case, a crane is needed both at the preassembly site and at the launch site.

Partial preassembly (prepack assembly)
1. Construction of a prepack basically involves
the preassembly of the center section of the
saddle assembly. The four saddle panels are
connected to the two center beams with the
two saddle adapters and balk-connecting
stiffeners attached. The remaining panels
and beams are loaded on top of this prepack.
This allows a crane to off-load the entire
saddle assembly and place it directly onto
the inflated float.
2. Prior to assembly and launching of floats, the
assembly/launch site should be set up as shown on page 48.
Note. The crane should be placed as close as
possible to the water's edge. The air
compressor is positioned in front of the crane and the bridge trucks are placed on
either side of the air compressor(s).
3. Once the half-floats are connected and
positioned on the ground beside the crane,
the float inflation crew can inflate the floats.
4. While the floats are being inflated, the
saddle assembly crew places the hooks of the crane's lifting chains in the eighth recess of
both stiffeners on the prepack. Two tag lines
should also be attached to the prepack to
allow for better control during lifting.
9. The balk-connecting stiffeners are next
placed on top of the saddle adapters. These stiffeners are fixed to the saddle adapters by four stiffener pins (four pins are placed on
each stiffener). Curb adapters should be
pinned into the 10th recess on both the left
and right side of the stiffener. The substructure is now complete.
10. Secure all panels to the float. Run the straps
attached to the outside of the float through
the handle on the panel above it. If possible, the straps should also be run through the handle on the saddle beam above the panel.
The straps below the outrigger panels are
attached to the outrigger beam. Next, fold
the strap in half and run it back through the
D-ring to provide a quick release.
11. Once the float is completely assembled, and
two tag lines (ropes) are attached to the float, the float rollers may be inflated. Inflation should begin with the roller closest to the water and worked towards the rear of
the float. Each roller is filled to a pressure of 2 psi, using an air compressor. Members of the saddle assembly crew should man the tag lines during float roller inflation.
12. Once roller inflation is completed, the float
can be pushed into the water, either by hand or by the bridge truck. When the float is in the water, the saddle assembly crew can retrieve the rollers and position them for the
next assembly and launch.
Preassembly of Bays To decrease the assembly time along the river line, bays may be preassembled in rear areas and driven forward on 5-ton bridge trucks or trailers. Normally, bays will be only partially

5. Once the floats are inflated, the saddle
assembly crew secures the tag lines to help control the placement of the prepack onto
the float. The NCOIC of this crew directs
the crane operator to place the prepack onto
the center of the inflated float using standard
hand signals. The float can now be
completely assembled as previously described in the discussion of manual assembly.
6. When assembly is complete, the saddle
assembly crew places the hooks on the lifting
chains in the eighth recesses on the stiffeners
once again. Tag lines are attached to the
cleats on the float's end beams and the
saddle assembly crew secures these lines.
The NCOIC can now direct the crane
operator to lift the entire float and place it
into the water.
Establishing a Balk Pattern Normal deck balk is used to provide the roadway decking for M4T6 rafts and bridges.

The placement of this balk provides the only means of connecting one float to another.

Twenty-two pieces of normal balk are placed on each floating bay to accomplish this task. The correct placement of this balk is essential in providing adequate roadway and correct bay to bay connections. To establish this correct balk pattern, it is first necessary to understand the terms surrounding the balk-connecting stiffeners to which the balk is attached.

Balk-connecting stiffeners As stated previously, each balk-connecting stiffener has 26 recesses, spaced 9.25 inches apart. These recesses are designed to receive the lugs on the bottom of the deck balk. Each of these recesses is assigned an identifying number as shown in the figure on page 48.

The outside recess on each end of the stiffener is given the number 13. The next recess, on the inside of recess 13, is assigned the number 12.

This continues to the center of the stiffener where the two center recesses are assigned the number 1.

Balk patterns The two types of balk patterns are normal and reinforced. Both patterns provide a deck which is 22 balk wide with 18 pieces of balk resting between the curbs. (Curb adapters are placed in the 10th recess on both the left and right side of the bridge.)
Normal. When constructing M4T6 normal rafts and bridges, a normal balk pattern is used to maintain a spacing of 8 feet 4 inches between the last stiffener on one float and the nearest stiffener on the next float (regardless of the type of saddle adapter). The figure at the right shows the methods of starting a normal balk pattern on various float combinations. When starting a normal balk pattern, place the near shore ends of the first two normal balk into the 11th recess on the left of and the 10th recess on the right of the stiffener closest to the shore. The next two normal balk are placed into the 10th recess on the left of and the 11th recess on the right of the second stiffener as shown in the figure.

Once the first four pieces of normal balk are placed and every lug is pinned as shown the remainder can be put into place (or placed on recesses 10 left and 11 right. The remainder of the bridge will be constructed using a normal balk pattern (except for the reinforced end section on the far shore). The figure below illustrates the reinforced balk pattern extended through a 21-foot 8-inch overhang.

placed in every other recess between the first two. When the third float, equipped with normal saddle adapters, arrives at the bridge centerline, it will be joined to the second float by two normal balk. These two pieces of balk are placed in recesses 11 left and 10 right and two additional pieces will be placed into top of the float until the float has been moved upstream to where a bridge or raft is to be completed). When placing the remainder of the balk, be sure to maintain the staggered pattern initiated with the first four pieces of balk. Pin the center lugs of all normal balk as they are placed into a stiffener recess. The end lugs are pinned only when two pieces of balk meet in the same recess. The exceptions to this rule are
When constructing an H-frame for a freed bridge When initiating a balk pattern When adding a stiffener to a raft overhang In these situations, the end lugs on the balk are pinned temporarily until adjacent balk is placed and pinned. At that time, the temporary pins are removed, filler balk placed, and pins reinserted.

Reinforced. Offset saddle adapters are used to establish reinforced balk patterns.

Reinforced patterns are designed to reduce the float spacing when constructing reinforced end sections for normal bridges, or when building reinforced rafts and bridges. The procedures used to initiate a reinforced end section are shown in the figure at the right. Note that the second float is equipped with offset saddle adapters and that the adapters are positioned so that the stiffeners are offset toward the near shore. As shown in the figure, the first two normal balk are placed in the 10th recess on the left of and the 11th recess on the right of the stiffener closest to the near shore. These two balk connect all four stiffeners on both floats. If the third float has not arrived on the centerline by this time, the next nine pieces of balk can be

Constructing a Three-Float Cluster
A three-float cluster consists of one normal
bay (float) surrounded by two offset bays. Because this three-float cluster is used as the basis for all reinforced bridges and as the basis for
five- and six-float reinforced rafts, it is discussed here under General Construction and is referred to in the paragraphs explaining the assembly of those rafts and bridges. Construction
of a three-float cluster is accomplished as follows:
1. The first float constructed is an offset float.
Once constructed and launched, this bay
should be secured to the near shore so that the stiffeners are offset towards the far shore.
2. Next, a normal bay is assembled and
launched. This bay is placed as close as
possible to the far shore side of the first float.
3. Two pieces of normal balk are then placed to
connect these floats. As shown in the figure,
these balk are placed in recesses 10 left and
11 right (as seen from a position on the near
shore), connecting all four stiffeners on both floats. This establishes the reinforced balk
pattern.
4. If the third float has not arrived on the
centerline by this time, the next nine pieces
of balk can be placed in every other recess
between the first two. Pin all center lugs as
the balk are placed.
5. When the third float, equipped with offset
saddle adapters, arrives on site, it is
positioned on the far shore side of the
second float. This float is placed with its stiffeners offset towards the near shore.
6. Normal balk are now placed so that the lugs
on the balk will engage the two stiffeners on
the normal (center float) and the two
stiffeners on the offset third float. Pin all center lugs as the balk are placed.

Use of Balk Depressors There are two basic types of balk depressors:
manual and hydraulic. These balk depressors are furnished with the M4T6 bridge erection set and are used when the balk lugs will not fit easily into the recesses on the balk-connecting stiffeners. Balk depressors force the balk down into the stiffener and, at the same time, raise the stiffener up towards the balk.

To use the manual balk depressor-
1. Place the foot of the balk depressor on the
top of the piece of balk that needs to be
depressed.
2. Lock the hook at the end of the chain into
the stiffener, using a steel stiffener pin.
3. Pull the chain taut and lock it into the chain
lock at the foot of the depressor.
4. Two soldiers grasp the handle of the
depressor and pull down and away from the
balk,
To use the hydraulic balk depressor-
1. Place the jack over the center lugs of the
piece of balk that needs to be depressed.
2. Center the depressor assembly over the jack. 3. Attach the hooks on the depressor
assembly's chains to the lifting handles of the two adjacent balk.
4. Pump the jack handle, depressing the balk
and raising the stiffener to a point where the
balk can be properly pinned.
M4T6 RAFTING OPERATIONS
M4T6 Raft Design Criteria The M4T6 rafts are constructed using either a normal or reinforced configuration. Each raft provides a roadway width of 13 feet 10 inches.

When fully loaded, an M4T6 raft has a draft of
29 inches.

The primary considerations when deciding upon the type of raft to build include the desired MLC of the raft and the required load space of the raft. Also the number of rafts needed versus the availability of M4T6 equipment should be considered. One set of M4T6
can provide the commander with either one four-float normal raft, one five-float normal raft, one four- and five-float reinforced raft, or one six-float reinforced raft. The capabilities of these rafts are given in Table 13.

EXAMPLE: What is the classification of a four-float reinforced M4T6 raft operating in a current velocity of 5 FPS?

SOLUTION: Refer to Table 13. An M4T6
four-float reinforced raft can carry wheeled vehicles with an MLC of 50 or less and tracked vehicles with a classification of 55 or less (in a current of 5 FPS).

Load Space The available load space on each type of M4T6 raft is shown in Table 13. Rafts are loaded only in the space between the raft's outside floats. The raft overhangs are not loaded.

EXAMPLE: How much load space is available on a six-float reinforced M4T6 raft?

SOLUTION: Refer to Table 13. The six-float reinforced M4T6 raft has approximately 53.3
feet of available load space.

Raft Assembly Times Table 13 shows the amount of time required to construct four-, five-, and six-float M4T6 rafts.

The construction times given are for assembly by hand with an experienced platoon under daylight conditions. Assembly times increase by 50 percent at night.

EXAMPLE: What is the assembly time for the construction of a five-float reinforced M4T6 raft at night?

SOLUTION: Refer to Table 13. Three platoon hours are required for the construction of a five-float raft during the day. Adding 50 percent for night assembly, the planned assembly time is 4.5 hours.

Classification of M4T6 Rafts The classification of M4T6 rafts is based upon the current velocity of the river at the rafting site. Table 13 provides the wheel and track classification of each type of M4T6 raft.

Equipment Requirements Construction All assembly sites for the construction of M4T6 rafts should be equipped with at least one 250 CFM air compressor, two BEBs, and either float rollers or a 20-ton capacity crane. Additional equipment requirements for specific rafts are shown in Table 14.

Rafting The M4T6 rafts are always propelled with BEBs tied off in a conventional configuration, as shown below. The number of boats needed to propel these rafts is based upon the velocity of the river. Table 15 shows the number of 27-foot BEBs required to push M4T6 rafts under varying current conditions. No formal tests have been conducted using the BEB-SD under water conditions.

fast the floats, connect the float straps, and thread nect the saddle beams, thread the bow and the connecting bar between the floats.

stern connecting bars, place the saddle adapters, and connect the stiffeners.

Organization for the Construction of M4T6
Rafts Under normal conditions, one combat engineer platoon can construct one M4T6 raft, under the supervision of at least one bridge sergeant. Personnel should be assigned to assembly parties as shown in Table 16. The float assembly crew is responsible for float inflation, saddle assembly, and launch. The duties of this crew, as well as those of the raft assembly crew, are described as follows:
Raft assembly The raft assembly crew positions the truck containing the balk and then places the balk on the floating supports.

Saddle assembly Two members from each saddle assembly crew assist in removing the saddle assembly from the truck. The other crew members place the panels on the inflated float, place and con-
Inflation Inflation crews unload the half-floats from the truck. They remove the carrying case, position the deflated float rollers (when used), inflate

overhang. To construct this overhang, add a stiffener to the ends of the balk that are
suspended from the near shore end of the
raft.
7. Add 11 pieces of normal balk, maintaining
the pattern already established. Place eight pieces of tapered balk in the remaining
recesses, with the tapered end connected to the last stiffener. Work from inside the curbs toward the center of the raft. This will leave the center of the raft open. Add four raft ramps to complete the overhang.
8. Spin the raft around and construct the
second overhang. This overhang is normally
a 15-foot overhang and is constructed in the same manner as the first.
balk the first two floats, the third and fourth
floats can be inflated and the saddle
assemblies placed on them. These are also
normal floats.
4. When the third float is constructed, it is
placed on the far shore side of the two floats
already in the water. The raft assembly crew
can attach this float with balk, continuing the initial balk pattern. Balk should be pinned in the center recesses only, and at points where two pieces of balk meet end to end.
5. The fourth float is added to the near shore
side of the raft in the same manner as the
other floats.
6. When all four floats are connected and
completely balked, the near shore overhang
can be built. This is normally a 15-foot
Construction of an M4T6 Four-Float Normal
Raft
A four-float normal raft consists of four normal bays spaced approximately 15 feet apart.
This raft is almost always built with two 15-foot
overhangs, but can be built with 23-foot 4-inch overhangs. The construction sequence is
generally described as follows:
1. Assemble and launch the first two floats.
Both of these floats should be equipped with normal saddle adapters.
2. Once the first floats are in the water, the raft
assembly crew can begin placing balk. Since normal construction is used, the balk is placed in recesses 11 left and 10 right, as
previously described. Balk should be placed
so that the lugs rest in two stiffeners on one
float and one on the other.
3. While the raft assembly crew continues to
Construction of an M4T6 Four-float
Reinforced Raft
A four-float reinforced raft is constructed by
placing a pair of side-by-side floats in the water.
It is normally equipped with a 15-foot overhang
at one end and a 21-foot 8-inch overhang on the other. The raft is constructed as follows:
1. Assemble and launch the first two floats.
One of these floats is equipped with normal saddle adapters, the other with offset saddle
adapters.
2. Once these bays are launched, the normal
bay is placed closest to the near shore. The
offset bay is placed on the far side of the normal float with the stiffeners offset
towards the near shore.
3. The two floats are joined using a reinforced
balk pattern. The first 11 balk should be
placed so that the lugs rest in all four
stiffeners. Pin all center lugs.
4. While the raft assembly crew is connecting
the first two floats, the float inflation crew
will inflate the third and fourth floats. The
saddle assembly crews can then emplace the saddle assemblies on these floats. Like the first pair of floats, one of these floats is a normal bay, the other is offset.
5. The third float launched should be the offset
float. It is placed on the far shore side of the
two floats already in the water. The stiffeners on this float should be offset towards the far
shore. Initiate a staggered balk pattern by
placing the frost two pieces of balk in
recesses 10 right and 11 left. These two balk
should start in the first stiffener of the
second float and reach across to the first stiffener of the third float, providing an
8-foot, 4-inch gap between the second and third floats. Now place two pieces of normal
balk one recess to the right of these two balk.
These balk should start in the second stiffener on the second float and reach across to the last stiffener on the third float.
Pin all center lugs and all end lugs where two
pieces of balk meet end to end.
6. The last float, a normal float, should be
moved to the far side of the three connected floats. Continue the reinforced balk pattern
already established and fill in the remaining
recesses.
7. Once the raft is completely balked, the first
overhang can be built. This is normally the
15-foot overhang. To construct the 15-foot
overhang, attach a stiffener to the ends of the
balk suspended from the near shore side of

## Construction Of An M4T6 Normal Raft Five-Float

The five-float normal raft is constructed in the same manner as the four-float normal raft except that a fifth float is added. (See figure.) The fifth float is normally positioned on the far side of the raft after the fourth float is connected.

Either 15-foot or 23-foot 4-inch overhangs may be used.

the raft. Fill in the recesses with 11 more
normal balk. Add eight pieces of short balk,
working from inside the curbs toward the
center of the raft. Add four raft ramps to
complete the overhang.
8. When the first overhang is completed, spin
the raft and construct the second overhang
(normally a 21-foot 8-inch overhang). To
build this overhang, frost add a stiffener to
the ends of the balk suspended from the raft.
Add 11 more normal balk.
9. Add another stiffener to the ends of the balk
just placed. Fill in the remaining recesses on
this stiffener with normal balk.
10. Complete by adding eight tapered balk,
pinning the tapered end to the last stiffener.
Work from inside the curbs toward the
center of the raft. Add four raft ramps.
Construction of an M4T6 Five-float Reinforced Raft The five-float reinforced raft is a three-float cluster with one normal bay attached to each side. Normally a 16-foot 7-inch overhang and a
23-foot 4-inch overhang will be constructed for this raft. Construction sequence is as follows:
1. Construct a three-float cluster. This cluster should be balked with 22 pieces of normal

balk. Refer to the figure on page 51.
2. While the raft assembly crew is balking the
three-float cluster, the next two floats can be
inflated and the saddle asemblies emplaced.
These floats are equipped with normal
saddle adapters.
3. Upon launching the fourth float, it is placed
on the far shore side of the three-float
cluster. This float is first connected to the cluster with two pieces of normal balk
following the balk pattern already
established. These balk start at the ends of the balk in the fourth stiffener (from the
shore) and run to the first stiffener on the
fourth float. These balk are placed in
stiffener recesses 11 left and 10 right.
4. Place two more pieces of normal balk
running from the sixth stiffener from the
shore. These balk will overhang 19 inches off
Note. If two 16-foot 7-inch overhangs are used then only two reinforcing balk are needed. If two 23-foot 4-inch overhangs are built then four reinforcing balk are required.

the last stiffener on the fourth float. These
balk are placed in stiffener recesses 10 left
and 11 right.
5. Add 18 normal balk, following the
established balk pattern.
6. Add the fifth float to the near shore side of
the raft. Connect this float in exactly the
same manner as the fourth float.
7. Construct a 16-foot 7-inch overhang from the
near shore float. This overhang is built by first adding a stiffener to the ends of the suspended balk. Fill in the remaining recesses on this stiffener with 11 more normal balk.
8. Add a stiffener to the ends of the suspended
normal balk (just added) and fill in the
recesses on this stiffener by adding 11 more normal balk.
9. Complete the overhang by adding eight
pieces of short balk, working from inside the
curbs to the center of the raft. Add four raft
ramps.
10. Spin the raft and construct a 23-foot 4-inch
overhang. This is done by adding a stiffener to the ends of the suspended balk, and filling in the recesses with 11 normal balk. Add a stiffener to these balk and fill in the recesses
with 11 more normal balk. Add one more
stiffener and fill the recesses with 11 additional normal balk. Add eight tapered
balk, pinning the tapered end to the
stiffener. Work from inside the curbs to the
center of the raft. Complete the overhang by
adding four raft ramps.
11. Add three pieces of reinforcing balk as
shown on page 57,
Construction of an M4T6 Six-float
Reinforced Raft
A six-float reinforced raft is constructed by
connecting a pair of three-float clusters. The
space between the two clusters is 6 feet 8 inches. This raft is built as follows:
1. Construct a three-float cluster.
2. Construct a second three-float cluster. 3. Connect the second three-float cluster to the
first using 11 pieces of normal balk. These
balk are placed on the fourth stiffener (from
the shore) and extend to the near shore
stiffener on the fourth float.
built using the successive raft method of assembly. Normal bridges can be built either using the successive bay or successive raft method. When designing M4T6 bridges, the required classification of the bridge and the quantity of M4T6 equipment available are critical considerations. Additional considerations include the required assembly time, the number of assembly sites needed, and the crew size required for construction of the bridge.

4. Place 11 more normal balk. These balk are
placed on the sixth stiffener (from the shore)
and extend to the near shore stiffener on the fifth float.
5. Fill all remaining recesses with normal balk.
6. Normally a 15-foot and a 21-foot 8-inch
overhang will be constructed for this raft.
The 15-foot overhang is constructed first by
adding a stiffener to the balk suspended
toward the near shore. Fill in the remaining
recesses with 11 more normal balk.
Complete the overhang with eight pieces of
short balk, working from inside the curbs toward the center of the raft. Add four raft ramps.
7. Spin the raft and construct the 21-foot 8-inch
overhang. Add a stiffener to the suspended
balk. Fill in the recesses with 11 more normal balk. Add another stiffener to the ends of
these balk. Fill in the recesses with 11 additional normal balk. Complete the
overhang with eight pieces of tapered balk and four raft ramps.
8. Add three pieces of reinforcing balk as
shown on page 59.
Note. If two 15-foot overhangs are built, only
two reinforcing balk are needed. If two 21-foot 8-inch overhangs are used, four
reinforcing balk are required.
For *reinforced construction,* the number of floats needed is determined using the following formula:
Number of floats
= (Gap(ft)) x 1.1
10
OR
Number of floats
= (Gap(m)) x 1.1
3
Because reinforced construction involves the assembly of a series of three-float clusters, the total number of floats must be rounded up to a number divisible by 3.

EXAMPLE:
How many floats are required to construct an M4T6 reinforced bridge across a 500-foot gap?

SOLUTION:
Number of floats
= (500) x 1.1 = 55 floats
10
Note. This number must be rounded up to a number divisible by 3. Therefore, the total number of floats needed is 57. Of these 57 floats, one-third will be normal floats and two-thirds will be offset floats since there is one normal float and two reinforced floats in every threefloat cluster. Of the total 57 floats, 19 must be normal floats and 38 will be offset floats.

Table 17 shows the personnel and equipment required for construction of normal and reinforced bridges of varied lengths.

Determining the number of floats required

The number of floats needed to construct a bridge will vary with the width of the gap and the type of bridge (normal or reinforced) to be constructed.

For _normal construction_, the number of floats needed is determined using the following formula:

Number of floats

= (Gapft + 2) x 1.1

15

**OR**

Number of floats

= (Gap(m) + 2) x 1.1

F.6

EXAMPLE:

How many floats are required to construct an M4T6 normal bridge across a 500-foot gap? SOLUTION

Number of floats

= (500 + 2) x 1.1

Number of floats = 38.86 so round up to 39 floats
M4T6 BRIDGING OPERATIONS
M4T6 Bridge Design Criteria The M4T6 bridges can be constructed in either a normal or reinforced configuration. Reinforced bridging is generally preferred because of the increased classification afforded by this type of construction. Reinforced bridges are Bridge Assembly Times The time needed to assemble a floating bridge may be effected by any number of factors.

Generally, M4T6 floating bridges can be constructed by one company at a rate of 150 feet every 4 hours, during the day. Table 18 gives the assembly times and recommended crew size for varying lengths of M4T6 bridges. The times shown are for daylight construction with experienced crews. Construction times should be increased by 50 percent for assembly at night.

EXAMPLE: What size unit is needed to construct an M4T6 normal bridge across a 500-foot gap and how long would construction of this bridge take at night?

SOLUTION Refer to Table 18. Two companies should be used to construct this bridge. The construction time given is 6 hours, but this is for daylight construction. Adding 50 percent for night assembly, the required construction time is 9 hours.

Classification of M4T6 Bridges Bridge classifications are based upon the type of bridge constructed and the current velocity.

Table 19 on page 62 shows the classification of M4T6 normal and reinforced bridges for varying currents and for normal, caution, and risk crossings.

Construction of M4T6 Normal Bridges Assembly crews The crews shown in Table 20 on page 63 are required for M4T6 construction using either method of assembly. The duties of the crews do not differ between the two methods of assembly, except for those personnel in the raft assembly crews. When building bridges using the successive raft method, these personnel construct two-, three-, or four-bay floating supports rather than single bays. Otherwise, the duties of these crews are as follows:
Balk carrying. This crew unloads and carries balk for each end section. When end sections are complete, all carriers unload and carry balk for each bay of bridge.

carrying cases when floats are preassembled form and places not loaded in the floats over the float rollers and connects them. While floats are being inflated, the saddle assembly crew unloads the saddle assembly from the truck and, after inflation places the saddle assembly, saddle adapters, and stiffeners with curb adapters on the float. After assembly they launch the float.

Float assembly. The float assembly crew is divided into a float inflation crew and a saddle assembly crew.

Float inflation. This crew inflates the prepositioned half-floats. Upon completion of the saddle assembly, the inflation crew inflates the float rollers and retrieves and repositions them for the next float inflation (if float rollers are used).

This crew assists the air compressor operator in setting up for float inflation.

Balk laying. This crew constructs the near shore end section, using one half of the balk carrying crew. After the end section is complete, the crew places and pins balk in the floating supports as they are added to the bridge.

Float delivery. This crew delivers completed floating supports to the bridge centerline, using a BEB.

Saddle assembly. This crew unloads the two half-floats from the bridge truck, removes the Anchorage. This crew installs anchorage cables, bridle lines, anchor towers, deadmen, and approach guys as needed.

Near shore abutment crew. This crew prepares the near shore abutment and assembles the 21-foot 8-inch end span on the near shore. This crew also places handrail posts and attaches handrail lines.

Far shore abutment crew. This crew constructs the far shore end section with the assistance of one half of the balk carrying crew. They prepare the far shore abutment and complete the assembly of the far shore end section.

Abutment preparation in construction of normal bridges Near shore. The near shore abutment must be prepared as soon as possible to allow for the construction of this end section. Only the work needed to position the abutment sill in its final position should be initially performed, since the abutment may need to be repositioned prior to final bridge closure.

Far shore. The far shore abutment crew and one half of the balk carrying crew construct the far shore end section, using the first, second, and third floating supports constructed at the assembly site. The next three floats constructed are used in the assembly of the near shore end section.

Constriction of a reinforced end section
All normal bridges are constructed with two
reinforced end sections.
1. Two floats are placed at the float assembly
site and lined up on their centerlines. These floats are spaced as close together as possible. The near shore float is equipped with normal saddle adapters. The second
float is equipped with offset saddle adapters
and is positioned so that the stiffeners are offset towards the near shore. Two normal
balk are placed so that they extend across all
four stiffeners. These balk are placed in the
number 11 recess to the right of the bridge centerline and in the number 10 recess to the
left. The balk are pinned at the center. If the third float has not arrived on the centerline,
the next nine balk are placed in every other recess between the first two.
2. The third float is a normal float and is moved
into position on the far shore side of the first two. Two pieces of balk should be used to connect this third float to the second float. These balk are placed in the number 10 recess to the right and the number 11 recess
to the left of the bridge centerline. These
balk should engage both stiffeners on the
second float and should run to the first stiffener on the third float. Pin these balk in the center lugs only.
3. Place two normal balk in the number 11
recess on the right and the number 10 recess
on the left of the bridge centerline. These two balk should engage both stiffeners on the third float and should run to the second
stiffener on the second float. Pin these balk
in the center recesses.
tached to these floating sections. After completion of the raft, 20 normal balk are loaded on the floating section. These balk are used to connect the raft to the bridge. Two additional balk are placed onto the raft, extending 8 feet 4 inches beyond the last stiffener. These two balk are pinned only at one end to allow them to be raised and connected into the bridge.

4. Now the balk needed to complete the deck
are carried forward, placed, and pinned
IAW the balk pattern established. A reinforced end section is constructed with a
deck width of 26 balk. When constructing the bridge using the successive raft method,
balk are placed on the third float for use in
the connection of the first raft to the end section.
Bridge connection Normal bridges can be built using either the successive bay or successive raft method.

stiffener and pickets are driven on either side of the centerline to mark the stiffener's final position.

EXAMPLE: If the distance measured between the far shore stiffeners on both ends of the bridge is 82 feet 4 inches, how far must the near shore abutment be moved to allow for final connection of the bridge?

SOLUTION: Since the measured gap is 82
feet 4 inches, the next higher multiple of 15 is 90 feet. Subtracting 82 feet 4 inches from 90 feet, the distance the near shore end section must be moved is 7 feet 8 inches. Measure 7 feet 8 inches back from the current position and drive pickets to mark the new location.

Overhang assembly The 21-foot 8-inch overhang is normally assembled by extending the balk pattern established by the near and far shore end sections.

The end stiffener is equipped with two abutment bearing plates. The spaces are filled in with normal and tapered balk. The tapered balk are placed with the tapered end toward the bridge. A 15-foot noncontinuous approach span extending beyond this abutment stiffener is desired. Eighteen tapered balk, placed side by side, are used for this approach from the ground to the overhang.

Closing the gap The near shore end section should be raised and moved as previously stated. A crane or bulldozer can be used to perform this task.

While final adjustments are made to the abutments, the remaining floats are added to the bridge. The near shore stiffener, with bearing plates attached, should be lowered into its final position onto the abutment sill. Balk can now be laid across the closing span. All balk should be pinned at both the interior and end lugs. Once all adjustments are complete, tapered balk can be laid, providing the approach span.

Successive bays. After the end sections are completed, single floating supports are brought upstream to the bridge site where they are connected into the bridge. These connections are exactly the same as the connection of the third float to the reinforced end section. The balk are unloaded from the trucks at the bridge centerline by the balk carrying crew and brought out to the balk laying crew which places the balk, connecting the floating supports. As bridge construction continues, the vehicle loaded with balk can be backed onto the partially completed bridge to reduce the distance that the balk must be carried. To ensure that an 18 balk roadway width is maintained, curb adapters are placed in the 10th recesses (left and right) of all stiffeners.

Construction of Reinforced M4T6 Bridges When constructing reinforced bridges, successive three-float clusters are used for each 30 feet of bridge length. Assembly crews are the same as those given for the construction of normal bridges using the successive raft assembly method. The method of construction is also exactly the same with two exceptions:
Adjusting the gap As soon as the gap is narrow enough to be measured accurately, the final position of the near shore abutment is determined by measuring the distance between corresponding stiffeners on the assembled portion of the bridge.

To close the bridge, this gap must be adjusted to a multiple of 15 feet. The measured distance is subtracted from the closest multiple of 15 feet to find the distance that the abutment stiffener must be moved, considering the fact that there must be 40 inches of water under the float closest to the shore and that the abutment sill should be 30 inches above the water level. This distance is measured back from the abutment Successive rafts. When constructing a bridge using the successive raft method, two-, three-, or four-float rafts are assembled and moved to the bridge centerline. A four-float raft is assembled using the same method as described on page 56. Obviously, the overhangs are not at-

Three-float clusters
four-float rafts.
are built instead of
center) from the shoreward stiffener on the
bridge.
5. Lay the balk, beginning at the bridge
centerline and working from the center of the bridge toward both sides. Pin each lug as
the balk is placed.
Eighteen tapered balk are laid for the shore
approach span. A sill is placed under the
shoreward end of these balk.
Twenty-two balk (either short or normal) are
laid for the shore transition span.

During rafting operations. there is little that can be done to prevent this grounding, but the raft commander can take care to ease the raft into and away from the shore to minimize possible damage. When bridge end sections are grounded, the floats are particularly vulnerable to wear from contact with the riverbed. Unless the bottom is protected, the float will wear through in 12 to 18 hours of continuous use. One method of protection is to lash a timber frame to the bottom of the pontons. This frame can be constructed of 2- by 12-inch timbers.

Place three 15-foot timbers along the length of the float and four 8-foot timbers along the width of the float.

Twenty-two short balk and 44 normal balk are
laid in a normal staggered pattern to form a 38-
foot, 4-inch *superimposed deck.* This superimposed deck runs from the first to the sixth stiffener placed on top of the bridge.
Twenty-two balk (either short or normal) are
laid for the *deck transition span. This* span runs
from the sixth to the seventh stiffener placed on
top of the bridge.

Eighteen tapered balk are laid as an approach
to the deck transition span.
6. Check all lugs to ensure they are securely
pinned. Place cover plates at all hinged joints.
7. Fasten wire rope lashings to the ends of the
stiffeners placed on top of the bridge to hold the superimposed deck in place.
Repair The air pressure in pneumatic floats changes with the temperature and the weather. Floats should be inspected frequently to ensure a constant pressure of 2 psi is maintained. Temporary repairs to floats are limited. Small holes may be plugged with the tapered plugs supplied in the emergency repair kit. If a float is damaged to the extent that the hole or tear cannot be repaired, the float will have to be removed from the bridge. Once removed, this float should be inflated and the extent of the damage should be determined. It maybe necessary to replace one or more of the tubes which make up the float if damage is severe. A severely damaged float may be removed from the bridge and another float may be installed without breaking the bridge connection. This may be accomplished by

The end sections are further reinforced to
match the capacity of the three-float
clusters used to construct the bridge.
Note. The end sections on reinforced
bridges are also constructed from threefloat clusters.
The method of constructing this end section is
described as follows:
1. The abutment sill is reinforced to support a
100-ton load. The level of the abutment may
range from the level of the bridge deck to 30 inches above the level of the bridge deck.
Refer to *TM 5-312* for additional guidance in
constructing a reinforced abutment sill.
2. Construct a 21-foot 8-inch overhang, as
previously described and move the end
section into position on the abutment sill. No curbs should be placed on this end section.
The raised curb would interfere with the
construction of the superimposed end section.
3. Place seven stiffeners on the deck of the
three-float end section, starting about one
foot from the shore end of the end section. Space these stiffeners alternately at 8-foot 4-inch and 6-foot 8-inch intervals.
4. Construct a reinforced abutment sill 8 feet 4
inches (on center) from the first of these
seven stiffeners. A stiffener with abutment
bearing plates attached is centered on this
sill. The span constructed between this abutment sill and the first stiffener on top of the bridge is called the transition span. If normal balk is used in this transition span,
this span should be constructed 15 feet (on
Retracting the retainers holding the superstructure to the saddle beams and withdrawing the damaged float.

## Operational Maintenance Maintenance Of Floats Protection When The Bank Is On A Gradual Slope And The Water Is Shallow, The Pneumatic Floats At The Ends Of The Bridge Or Raft May Be Grounded. M4T6 Floating Bridges And Rafts 66

Pulling a partially inflated float (with a complete saddle assembly), beneath the bridge.

This is done after the damaged float is removed.

Working the saddle beams on the new float into position under the superstructure and replacing the retainer lugs.

Storage of floats
If floats are to be removed from the water for
3. Deflate the float completely. Powder the
an extended period of time, the following acfloat and store it in a cool, dry place. It is
tions are recommended
best to store floats in an area where they can
1. Deflate and remove all water from the float
be stacked flat (neither rolled nor folded).
using the inflator-deflator valve on the 250
When this is not possible, it is preferable to
CFM air compressor.
roll the floats rather than fold them.
2. Reinflate the float and allow it to stand. This
lets the float dry completely and provides a means to ensure that the float has no leaks.
Completely inflating the new float.

Bridge Maintenance Inspections The M4T6 bridges should be inspected frequently to ensure the bridge remains in safe, operational condition. Particularly ensure that connecting pins and safety pins are in their required locations and are serviceable. Decks must remain clean and inspect balk for signs of cracks or undue wear.

Trestles Transoms should be raised whenever a trestle shoe does not settle. Additional trestle bracing is usually needed after the initial settlement.

The bracing clamps should be adjusted and tightened to compensate for the bending caused by settlement. Use sandbags, wire netting, landing mats, or rocks to protect footings from the undercutting action of the current.

checked frequently and, when necessary, the banks should be stabilized with riprap or sandbags. Every effort should be made to anticipate water level changes which may necessitate lengthening the bridge or adding trestles.

Bridge approaches require continuous maintenance to avoid traffic delays caused by impassable approach conditions. Stockpile road materials to aid in repairs and improvements.

Abutments and approaches Check abutment shoes and sills for settlement. When they settle, use gravel, additional footing material, or cribbing to provide the necessary bearing area. Bank revetting must be End spans Continuous deck end spans frequently rise off the abutments. This tendency can be overcome by raising the height of the abutment and by ensuring that there is adequate bearing surface on the abutment.

## Chapter 6. Class 60 Floating Bridge

currents up to 8 FPS and bridges capable of are the same as that available in the M4T6
supporting MLC 65 traffic in currents up to 5
equipment set. Refer to Chapter 5 for addition-
FPS. Proper military nomenclature for this set al guidance relating to these components.

is the Bridge, Floating Pneumatic Float, Class
60, Steel Superstructure.

Superstructure The bridge superstructure is made up of the COMPONENTS
components discussed in the following Substructure paragraphs.

The pneumatic float and saddle assembly used for construction of Class 60 rafts and bridges Class 60 floating rafts and bridges consist of a deck constructed of flush surfaced steel-grid panels, supported by 24-ton pneumatic floats spaced 15 feet apart (center to center). Because of the weight of the individual components used to construct Class 60 bridges and rafts, these floating structures must be built using a 20-ton crane or a comparable lifting device. Class 60 equipment can provide the crossing force commander with rafts supporting MLC 70 traffic in Deck filler panels Each deck filler panel is approximately 14 feet
9.5 inches long and weighs 1,400 pounds. One deck filler panel is designed to rest between two deck tread panels.

Curbs Each set contains two types of curbing deck and short curbs. The deck curbs are a little over
14 feet long and weigh 325 pounds. These are placed along both sides of each bay of bridge.

Deck tread panels Each deck tread panel consists of two 18- by
7.5-inch wide flange 50-pound stringers. The deck panel has an open-grid deck, welded to the top flanges of the two stringers. The stringers are braced by welded diaphragms.

These panels are designed to rest on the saddle beams and are connected to adjoining bays by pins in the male and female end connections.

One deck tread panel is approximately 17 feet long and weighs 4,160 pounds.

Short curbs are 5 feet 4 inches long and weigh
125 pounds. They are placed on both sides of ramps and short bays.

Ramp tread panels The ramp tread panels are designed to provide an inclined approach to the raft or bridge. Each ramp panel is approximately 16
feet long and weighs 3,750 pounds. All ramp panels have female ends.

panels have two female ends and are connected to ramp tread panels by connector beams.

Ramp filler panels The ramp filler panel weighs approximately
1,180 pounds and is designed to rest between two ramp tread panels.

Connector beams Connector beams weigh 495 pounds and are used to connect ramp tread panels to either short deck tread panels or ramp deck tread panels. This connection can form either a level connection or an incline of 10 degrees (up or down).

Short deck tread panels Each short deck tread panel has an effective length of 5 feet 3 inches and weighs 1,660 pounds. These panels are used to construct short bays which are useful in adjusting the lengths of floating bridges. Short deck tread Short deck filler panels Short deck filler panels are 5 feet 4 inches long and weigh 510 pounds. These panels rest between the short deck tread panels on short bays and on ramp bays.

Cover plates The two types of cover plates are tread and filler cover plates. One filler cover plate and two tread cover plates are placed over the joint between the bridge deck and the ramp bay.

stiffener stop bar and the wider end is secured with the ramp stop bracket.

Anchorage set The anchorage set provides all of the materials needed to anchor the Class 60 bridge in currents up to 11 FPS. Refer to Chapter 8 for additional information.

Allocation of Class 60 Equipment Class 60 equipment is no longer authorized in active, reserve, or National Guard float bridge companies. All remaining Class 60 equipment is currently maintained in depot stocks. One set can be used to construct one floating bridge capable of spanning a 135-foot gap or one four-, five-, or six-bay raft.

Ramp stiffeners Ramp stiffeners are issued as part of the bridge set; however, under most conditions, they are not required or used in assembling the bridge. Ramp stiffeners add to deck efficiency but are needed only in situations in which abutment conditions are likely to bring about a major difference in settlement between two adjacent deck panels. Once used, the stiffener assembly cannot normally be reused because its members are bent when heavy loads cross the bridge. Where used, a ramp stiffener is installed transversely across each ramp bay. Two ramp stiffener sections are bolted together and placed through rectangular openings in the ramp tread panel stringers (at the shore end of the level part of the deck). The narrow end of the stiffener section is secured using a ramp Transportation and Loading of Class 60
Equipment One set of Class 60 equipment is normally transported on a total of 13 bridge trucks. One bridge truck is required to transport each of the nine bays of bridge, including a 24-ton pneumatic float, saddle assembly, and deck components. Additionally, 1 truck is needed to carry each of the two ramp loads, 1 truck carries the erection equipment, and 1 truck carries the anchorage set. Each truck can be loaded as described in Table 21.

communications, these ribbon bridges must be replaced with more permanent assets. Class 60
bridges, placed along MSRs might serve in this capacity. The major consideration in determining the location of such a bridge is the existence of a well-defined road network leading both to and from the bridge site. Other considerations include the availability of adequate assembly sites and sufficient depth of water at the bridge site. When planning to construct Class 60 rafts and bridges, also consider the availability of specialized equipment such as air compressors, cranes, and BEBs.

Considerations for Tactical Employment Because of the considerable time and number of personnel required to construct Class 60
rafts and bridges, this equipment will probably not perform a major role in the rafting phase or even in the early stages of the bridging phase of a deliberate river crossing operation. Class 60
rafts may be needed in situations when sufficient ribbon or M4T6 assets are not available to swiftly cross the desired number of armored vehicles. As the crossing force commander secures the bridgehead area and prepares to move forward, consideration is made for removing the ribbon bridges to deploy them with the advancing forces. To sustain lines of GENERAL CONSTRUCTION
Class 60 floats, because of their weight, are normally assembled with the use of at least one crane. Two cranes should be positioned at each assembly site for maximum efficiency in construction. The basic substructure of the Class 60
bridge or raft is the same as for M4T6 floating equipment and can be assembled in the same manner.

Assembly and Launching of Floats Using Two
Cranes
An illustration of a typical float **assembly** and
launch site is shown at left. The general sequence for construction is given below:
1. Two uninflated half-floats should be laid out
stern to stern. These half-floats are
connected by threading a connecting bar through the flaps on the bottom of each float
and buckling the crisscross straps at the top
of one half-float to the D-rings of the other.
2. Next, inflate the float, working from the stern
to the bow. There are four compartments in
each of the three tubes which make up each
half-float. Each compartment should be filled to a pressure of 2 psi, using a 250 CFM air compressor, or the equivalent.
3. Once the floats are inflated, the saddle
assembly crew can emplace the saddle assembly. When constructing Class 60 floats
in this manner, the saddle assembly is normally carried to the river in a partially
assembled configuration. This preassembled section is the same as the prepack described in Chapter 5, with the omission of the saddle adapters and stiffeners.
the D-ring on the float to provide a quick
release.
7. Once the float is completely assembled and
two tag lines (ropes) are attached to the
float, the float should be lifted by the crane
and placed into the water. Once in the water, the float can be moved upstream to have the
superstructure (deck) placed on it.
8. After the float is launched, the truck which
carried the bay is positioned by the deck assembly site. The deck tread and filler
panels are raised and positioned by the crane, using a chain sling with two legs and special hooks. These slings are included in the erection set.
4. When loaded on the bridge truck, the end
beam and outrigger beam sections are
nested on top of the center beam section so that the crane can remove all five sections in one lift, placing the assembly on the center of the float. Once the prepack has been
placed onto the inflated float, the end beam
sections and outrigger sections are installed.
If the saddle assembly is not preassembled in the reamer described above, it should be built by hand as explained in Chapter 5.
5. Once the saddle beams are in place, the two
connecting bars are installed. Prior to installing one connecting bar to each end of
the float, remove the guide pins from each of the outrigger beams. This will allow the
beam to be raised or lowered as needed
without great difficulty. Each connecting bar
should be threaded through the outrigger
beams and the holes provided in the bow
end of the float. Push up on the ends of the
float to reinstall the guide pins. All panels should be attached to the saddle beams at this time.
6. Secure all panels to the float. Run the straps
attached to the outside of the float through
the handle on the panel. Attach the straps
below the outrigger panels to the outrigger beam. When possible, run all straps from the
handle on the saddle panel through the
handle on the saddle beam above it. Next,
fold the strap in half and run it back through
11. Secure curbs to the outside stringer on the
deck panels with shouldered capscrews or
bolts to complete the bay.
Uses of roller conveyors or float rollers Roller conveyors. The same type of roller conveyor that is used in depots and warehouses can be useful in moving floats across a beach.

The standard roller conveyor is a 10-foot aluminum roller section which weighs about 70
pounds. Steel rollers are also fairly common. These steel roller conveyors normally weigh about 165 pounds. Two possible uses for roller conveyors when establishing a Class 60 float construction and launch site are shown.

9. Position the deck tread panels against the
sliding deck panel retainers on the saddle beams with the bottom lugs straddling the
saddle beams. Drive the sliding retainers up
tight on the stringer flanges and secure with
safety pins. Place the tread panels with the
male end towards the far shore to simplify
the far shore connections.
10. Secure a filler panel to the inside of the deck
panels with eight shouldered capscrews or
bolts.
Expedient Methods of Bay Assembly There are several means of assembling Class
60 floats when an insufficient number of cranes are available. These methods include the use of roller conveyors or float rollers, expedient lifting devices such as A-frames and gantry frames, and preinflation and transportation of completed Class 60 bays.

Float rollers. Use the same pneumatic float rollers described in Chapter 5 in launching Class 60 floats. Round poles, 6 to 8 inches in diameter and approximately 10 feet in length, can be fitted with plank treads and used in the same manner.

Expedient lifting devices The use of expediently constructed lifting devices is limited only by the materials available and the imagination of the bridge crew. The standard Army 5-ton wrecker has readily installed outriggers, a hydraulically controlled boom of 18 feet maximum reach, a rear winch with a 45,000-pound capacity, and a front winch with a 20,000-pound capacity. A-frames can be constructed for any military vehicle using components of a bridge trestle arrangement. Gantry frames like the one shown on page 78 can also be used to place deck on a float.

Preinflation and transportation of preassembled bridge bays It is possible to preinflate and assemble Class
60 floats in the equipment park and transport these bays to the river using the bridge transporter or low-bed trailers. When using a trailer to launch Class 60 bays, rollers should be attached to the trailer bed to simplify the launch procedures. Floats that are loaded onto trailers must be securely tied or chained in place prior to transportation.

Connection of Bays
The connection of Class 60 bays is a relatively
simple process.
1. The members of the bay connecting crew
first pull the two bays into position, using tag
lines.
2. The bays may need to be aligned prior to
connection. This alignment is accomplished
with a spacer gage. Lugs welded to the end
of the spacer gage hook into the handles in the saddle beam end sections and position the floats accurately in relation to each other. Spacer gages can be locally fabricated as shown on page 79.
3. Once the floats are properly spaced, the
male ends of the deck tread panels of one
float can be inserted into the female ends of
the other. Prior to connection, the interior pin on the female end of each deck tread
panel should be installed and secured with a safety pin to act as a guide pin. Once the panels are aligned, they can be secured with
a second connecting pin.
CLASS 60 RAFTING OPERATIONS
Raft Design Criteria Class 60 rafts can be constructed using either a normal or reinforced configuration. Each raft provides a roadway width of 13.5 feet and when fully loaded, has a draft of about 29 inches. The primary considerations when deciding upon the type of raft to construct include the desired MLC of the raft and the required load space. One set of Class 60 equipment can provide the crossing force commander with sufficient materials to construct one four-, five-, or six
bay raft. The capabilities of each of these are given in Table 22.

Assembly Times The US Army currently has little experience in the construction of Class 60 rafts. It is extremely difficult to provide an accurate estimate of the time required for construction. As a planning figure, at least 3 hours should be provided for the assembly of Class 60 rafts under ideal conditions.

Equipment Requirements All assembly sites for the construction of Class
60 rafts should be equipped with at least one 250 CFM air compressor, two BEBs, and two
20-ton capacity cranes. If two cranes are not available, the floats can be constructed by hand and launched using roller conveyors or float rollers. One crane must be available at each site to lift the deck components and place them onto the completed floats.

Construction Of Class 60 Rafts varying current conditions. At this time, no for-
Organization for assembly mal tests have been conducted using the BEB-
Under normal conditions, one combat en-
SD to propel Class 60 rafts.

gineer platoon can construct one Class 60 raft, Load Space The available load space on each type of Class
60 raft is shown in Table 22. Only the deck bays are loaded. Vehicles are not placed on the raft's ramps.

EXAMPLE: How much load space is available on a five-float reinforced Class 60 raft constructed with three normal deck bays and one short deck bay?

SOLUTION: Refer to Table 22. The five-float reinforced Class 60 raft with three normal deck bays and one short deck bay has approximately
43 feet 9 inches of available load space.

Classification Of Class 60 Rafts The classification of Class 60 rafts is based upon the current velocity of the river at the rafting site. Table 22 provides the wheel and track classification of each type of Class 60 raft.

EXAMPLE: What is the classifiation of a four-float normal Class 60 raft operating in a current velocity of 5 FPS?

SOLUTION: Refer to Table 22. A four-float normal Class 60 raft can carry wheeled vehicles with an MLC of 40 or less and tracked vehicles with a classification of 45 or less (in a current of
5 FPS).

Required Number of Boats Class 60 rafts are always propelled with BEBs tied off in a conventional configuration. The Class 60 raft is propelled through a trestle column hung across the sterns of two floats and lashed to the saddle beam cleats as shown in the figure. The number of boats needed to propel these rafts is based upon the velocity of the river. Table 23 shows the number of 27-foot BEBs required to push Class 60 rafts under Raft assembly. This crew positions the truck containing the deck and then places the deck on the floating supports.

under the supervision of at least one bridge sergeant. It is recommended that personnel be assigned to assembly parties as shown in Table 24. The duties of each crew are generally described as follows:

2. Configure the third float launched as a ramp
bay. It is assembled from two ramp tread
panels, one ramp filler panel, one short deck filler panel, and four short deck curbs. The
ramp filler panel covers the sloping part of the ramp and the short filler panel covers the level part. (See figure on page 82.)
3. Using two connector beams, attach the third
float (the ramp bay) to the far shore side of the two floats that were previously
connected. Deflate the float which supports
the ramp bay and remove it, leaving an
overhang on the far shore side of the raft.
Construction of Class 60 normal rafts Normal rafts are all constructed in the same manner. Each normal raft consists of a number of normal deck bays spaced 15 feet apart with a ramp connected to each end. The construction sequence for a four-float normal raft is provided below
1. The first two floats are constructed and launched. Once these floats are in the water, the raft assembly crew can place the deck on each of these floats and connect the two floats together.

Float assembly. Each float assembly crew is divided into an inflation crew and a saddle assembly crew.

Inflation. This crew unloads the half-pontons from the truck, removes the carrying case, inflates the floats, connects the float straps, and threads the connecting bar between the floats.

Saddle assenbly. This crew assists in unloading the saddle assembly, places the preassembled section on the inflated float, places and connects the end beams and outrigger beams, and threads the bow and stern connecting rods.

process, connection of the ramps can be difficult and time consuming.

Construction of Class 60 reinforced rafts Refer to the figure on page 83. The most commonly constructed Class 60 raft is a five-float reinforced raft constructed with three normal deck bays and one short deck bay. This raft is constructed as shown in the figure on page 84.

This overhang will keep the near shore end
of the raft slightly elevated which will
simplify the positioning of subsequent floats.
4. Once the far shore ramp is connected, add
the fourth normal deck bay to the near shore
side of the raft.
5. Assemble a ramp bay using the float which
was removed from beneath the far shore
ramp. Attach this bay to the near shore end
of the raft.
6. Attach ramp control brackets.
7. Deflate and remove the float supporting the
near shore ramp.
8. Attach the required number of BEBs and
install the ramp yokes (guide pins) prior to loading traffic across the ramps.
One variation of the above procedure is to
launch all four floats, and construct four normal
bays. After connecting these bays, use the crane
to emplace the ramp tread panels on the near
and then the far shore ends of the raft. Although this method of assembly is a simpler
Ramp control expedients When rafting, it is often necessary for the raft crew to adjust the angle of inclination of the ramps. To do this, bolt an expedient ramp control bracket to the outer stringer of each ramp deck panel. When the tops of these brackets are connected by cables, or are fastened to some point on the deck panel stringers by chain hoists, this arrangement permits the raft to be propelled with the ramp bays approximately level, but not pinned at the level position. When using this expedient, securely bolt the filler panels on the sloped portion of the ramps in place to prevent any spreading or binding of the ramp bays. When loading or unloading the raft, adjust and pin the ramps in a suitable position using the ramp yokes (guide pins). There are two methods of controlling this ramp adjustmentmanual and mechanical.

Manual. This method requires that connector beams be installed at both ends of the raft, between the last deck bay and the ramps, to permit a hinged connection at each end. The rafting brackets should be connected with l/2-inch cable and a chain hoist. The chain hoist is then used to counterbalance both ramps. When properly counterbalanced, the weight of one or two soldiers on the outer end of a ramp is adequate to move either ramp downward far enough to pin the shoreward ramp in the desired position.

Mechanical. In this method, a chain hoist and a length of 1/2-inch cable is used to connect each bracket to one of the lifting eyes on a deck tread panel. This method, as shown in the figure on page 88, permits independent adjustment of each ramp or permits omission of the connector beams at one end of the raft (if that ramp requires no adjustment due to shore conditions).

CLASS 60 BRIDGING OPERATIONS
Class 60 Bridge Design Criteria Class 60 bridges, unlike M4T6 bridges, are constructed only in a normal configuration.

These normal bridges can be built with a reinforced end span, if desired, to increase the ability of the bridge to cross heavy traffic. Normal bridges must be constructed with a reinforced end span if vehicles larger than MLC 55
are expected to cross the bridge. The required classification of the bridge is obviously most critical. Additional considerations include the quantity of Class 60 equipment needed to bridge a given gap, required assembly time, the number of assembly sites required, and the crew size needed for the construction of the bridge.

Determining Float Requirements The number of floats needed to construct a bridge will vary with the width of the gap and the type of end span (normal or reinforced) to be constructed.

Class 60 bridges with normal end spans

The number of floats needed is determined using the following formula

Number of floats = (Gap (ft) x 1.1

OR

Number of floats = ( Gap (m) x 1.1

4.6
EXAMPLE: How many floats are required to construct a Class 60 bridge with a normal end span across a 500-foot gap?

SOLUTION:
Number of floats = (500) x 1.1 = 33.33 x 1.1
15
Number of floats = 36.67, so round up to 37
floats

Class 60 bridges with reinforced end spans The number of floats needed is determined using the following formula:

Number of floats = ( (Gap (ft) ) + 2 ) x 1.1

OR

Number of floats = ( (Gap (m) ) + 2 ) x 1.1

4.6

Note. The two floats added are used to construct the reinforced end spans (one extra float in each end span).

EXAMPLE: How many floats are required to construct a Class 60 bridge with a reinforced end span across a 500-foot gap?

SOLUTION:

Number of floats = ( (500) + 2 ) x 1.1 =

38.86 floats, so roundup to 39 total floats.

Personnel and Equipment Requirements Table 25 on page 88 shows the manpower and equipment required for construction of Class 60 bridges in varied lengths.

mended crew sizes for varying lengths of Class 60 bridges. The times shown are for daylight construction under ideal conditions. Construction times should be increased by 50 percent for assembly at night.

How long would construction of this bridge take at night?

SOLUTION: Refer to Table 25. Two companies should be used to construct this bridge. The construction time given is approximately 5
hours (this is for daylight construction). Adding 50 percent for night assembly, the required construction time is determined to be 7.5 hours.

EXAMPLE: What size unit is needed to construct a Class 60 bridge across a 500-foot gap?

Assembly Times for Class 60 Bridges The US Army has little experience in the construction of Class 60 bridges. Table 25 shows the estimated assembly times and recom-
FPS is MLC 55 for wheeled vehicles and MLC 65 for tracked vehicles.

Refer to Table 27. The classification of a 15-
foot normal end span is MLC 55 for both wheeled and tracked vehicles.

Comparing the classifications of the floating span and the end span, the final classification of the bridge is determined to be MLC 55 for wheeled vehicles and MLC 55 for tracked vehicles.

Construction requirements Assembly crews. The crews shown in Table 28
on page 91 are recommended for the construction of Class 60 bridges.

Construction of end sections. The Class 60
floating bridge is normally assembled from near shore to far shore. The number of raft assembly sites available and the width of the river may affect this decision. If raft assembly sites are limited, it may be better to assemble from the far shore to the near shore to permit use of the near shore abutment area as a raft assembly site. FOr very wide river, it maybe preferable to assemble the bridge from both shores to the middle of the bridge span. Position the first floating support at a location where the water is at least 3 feet deep.

Normal. To construct a 15-foot nornal end section, launch three floats. Construct three normal bridge bays (using two deck panels, one filler panel, and two deck curbs on each bay)(.

Connect the bays and position them at the bridge centerline. Using a crane, attach two ramp panels to the first normal bay. Complete the end section by adding one short filler panel, one ramp filler panel, and four short curbs.

Anchor the end section using two approach guys.

Reinforced. The reinforced end section is normally used for Class 60 bridges because of the increased classification it provideds. The procedures for constructing the end section are as follows:
1. Construct and launch three floats as previously described. Tie the floats flush against one another, using ropes attached to the mooring cleats on the end beams.

Classification of Class 60 Bridges Bridge classifications are based upon the clas-
SOLUTION: Refer to Table 26. The classification of the floating bridge itself and the sification of the floating span in a current of 5
classification of the bridge's end span. The classification of the floating span for various currents is given in Table 26 on page 89. Table 27
shows the classification of the different end spans which can be constructed. In determining the actual bridge classification, a comparison should be made between the classification of the floating span and that of the end span that must be constructed to complete the bridge. The lower classification of the two becomes the overall bridge classification.

EXAMPLE: What is the classification of a Class 60 bridge constructed at a site where the river's current flows at 5 FPS and the bridge is constructed with two 15-foot normal end spans?

(Assume a normal crossing.)
Construction of Class 60 Bridges Class 60 bridges are normally constructed using the successive raft method, that is, floating rafts are assembled at each launch site and are moved upstream to the bridge centerline.

2. Use a crane to lift the top deck panel off the
bottom deck panel while they are still on the
truck. Guide the female end of the top deck
tread panel into the male end of the bottom deck tread panel, using tag lines. Pin the
sections together and secure them with
safety pins.
3. Remove and reposition the Class 60 lifting
chains to enable the crane operator to lift the
connected sections.
Note. The sections can also be connected on
the ground.
4. Center the connected panels over the three
floats (on the downstream side) using the tag lines to help control the sections. Lower the sections, aligning them with the sliding
5.
6.
7.
retainer lugs on the downstream side of the
center beams, and secure them im place. Repeat the preceding steps for laying another two-panel section, on the upstream side of the float. After the second two-panel section has been
secured, set each filler panel in place
individually. Bolt each filler panel in place with eight bolts and emplace the curbs. This
completes the reinforced end section.
Two normal bays must be attached to the
reinforced end section prior to adding the
ramp tread panels. First, a BEB is tied to a
normal bay or to two connected normal bays. Then the bay(s) are taken to the reinforced
end section.
8. The sections are connected by inserting the
male end of deck panel on the reinforced end section to the female end of the first
normal bay. The vertical and hydraulic
aligning tools may be required to aid in
alignment of these additional bays.
structed in the same manner as the near shore end section. At a typical site, a bulldozer blade may be used to set the far shore ramp on its abutment. If a crane is used for positioning the ramp at the far shore, the near shore crane can cross over and operate from the partially completed bridge. The ramp bay can bear on the abutment sill at any point in the length of the Construction of the floating span. Once the near sjore end section is completed, construction of the bridge itself may begin. Rafts consisitng of two normal deck bays are assembled at the launch sites and carried upstream to the bridge centerline. All connections are made by the bridge assembly crew. Once the span is completed, the far shore end section is conare expected in the water level, give the ramp joint a freed support of adjustable height, and hinge the joint by ommitting the yoke (guide) pins. In either case, use cribbing to provide this fixed support, whenever possible. When cribbing cannot be used, the trestle crew must install trestle arrangements to provide the desired classification. Construct these trestles IAW Chapter 10.

## Maintenance Of Class 60 Rafts And Bridges Operational Maintenance Class 60 Bridges And Rafts Are Maintained In The Same Manner As M4T6 Equipment. See Chapter 5, Page 68.

ramp, so that a precise adjustment of bridge length is not necessary. However, the length of bearing must be at least 18 inches, to prevent the ramp bay from slipping off the abutment under traffic. In closing the bridge, if the final gap between the far shore end section and the first bay of the floating span is less than 15 feet, a short deck bay may be constructed and emplaced. Install cover plates over the joint between the bridge and ramp.

Fixed connections. If the length of the floating connection from the abutment sill to the nearest saddle beam exceeds 15 feet, the class of the end connection must be reduced, or an intermediate fixed support must be added to reduce the span length. If frequent or major changes

## Light Tactical Rafts And Bridges

footbridge can also be used to construct light floating bridges and is discussed in Appendix E.

COMPONENTS
Half-ponton The aluminum alloy half-ponton has an effective length of 18 feet 6 inches, is 6 feet 8.5 inches wide, and 2 feet 10 inches high. The bow of each half-ponton is raised approximately 7
inches higher than the stem to prevent the ponton from swamping when rafting in swift currents. The half-ponton weighs approximately
650 pounds and has a displacement of 6.25 tons.

Light tactical rafts (LTRs) and bridges consist of aluminum deck sections supported by aluminum pontons. One set of LTR equipment is most commonly used to construct a floating raft which can provide the crossing force commander with an MLC 16 capability in currents up to 7 FPS. The LTR equipment can also be used to construct light tactical bridges capable of crossing MLC 16 equipment in currents up to 5 FPS. The LTR can be used to cross lighter loads in currents up to 10 FPS. Proper military nomenclature for this set is Bridge, Floating Raft Section, Light Tactical Raft. Aluminum Two half-pontons are joined stem to stem to form a whole ponton which supports the light floating bridge or raft.

Deck Panels Each deck panel has an effective length of 11
feet and weighs 565 pounds. Two deck panels are placed side by side on a whole ponton (with a space between) to form one normal bay of LTR. The deck panels are held in place by four retainer lugs located on the pontons. Each deck panel has a male end and a female end.

ramp is slightly over 7 feet long 3.5 feet wide, and weighs 400 pounds.

Ramp Filler Panels Ramp filler panels are 3 feet long and weigh
65 pounds. These panels are used to fill the gap between two adjacent ramp panels.

Deck Filler Panels Refer to the figure on page 93. The deck filler panel is approximately one-half the effective length of a deck panel and weighs 95 pounds.

Two deck filler panels are used to fill the space between one pair of deck panels. Deck filler panels are normally held in position by pintles, but they can also be bolted directly to the deck panels.

Ramp Panels The two types of ramp panels in a set of LTR
are male and female. One like pair of ramp panels is used at each end of the LTR raft or bridge to allow for the loading and unloading of traffic. The male ramp panel is 8 feet long 3.5
feet wide, and weighs 330 pounds. The female Articulating Assembly The articulating assembly is provided to permit variations in the inclination of the raft ramps to allow for various shore conditions.

The articulating assembly allows the ramp panel to be raised up to 41 inches above and lowered to 19 inches below the horizontal. Each articulator weighs about 640 pounds and has a male section and a female section. A connecting pin and adjusting bar are used to join the two sections. A carrying bar is used to carry the newer model articulating assembly. The older version is equipped with carrying handles.

Curbs Two sizes of curb are used in assembly of LTR
rafts and bridges. Deck panel curbs are a little less than 11 feet long and are placed along both sides of normal LTR bays. Short curbs are almost 3 feet long and are placed along the ramps. Both types of curbs are held in position by holding lugs that extend from the bottom of the curb and bear directly on the underside of the top flange on the deck panel.

Other Accessories Additional items which are issued with the LTR include the following:
Anchors Two fluked, 30-pound, steel, marine anchors are issued on the basis of one per whole ponton.

Outboard motor brackets These brackets are used to connect outboard motors to the stern of LTR pontons. One motor bracket is issued for each whole ponton.

Ponton cradle The ponton cradle is issued on the basis of one per set of LTR. The cradle is placed on a 2 l/2-
ton pole trailer or on a 4-ton bolster trailer and is used to carry eight half-pontons.

Chain assembly with binders Four chain assemblies with binders are issued to secure the raft set during transportation.

CONSIDERATIONS FOR THE TACTICAL
EMPLOYMENT OF LTR
The LTRs and bridges will not normally be used during hasty river crossings, and are of very limited use during retrograde or deliberate crossings. The inability to carry heavy loads Holdfasts Four prefabricated holdfasts for use as anchorages are issued with the raft set. Nine steel pickets and a holdfast chain comprise each holdfast.

TRANSPORTATION OF LTR
The components of one set of LTR are normally carried on two 2 l/2-ton trucks and either one 2 l/2-ton pole trailer or one 4-ton bolster trailer. The chains and binders which come with the set are used to secure the components onto the vehicles. The cradle is used to nest the eight half-pontons on the trailer. More specifically, the trucks are loaded IAW Table 29.

ALLOCATION
Each set of LTR can be used to construct either a four-ponton, three-bay raft; a four-ponton, four-bay raft; or 44 feet of light tactical bridge. The LTR is not currently authorized by Table of Organization and Equipment (TOE)
in float bridge companies and its role in future river crossing operations is uncertain.

makes their value to the crossing force commander quite doubtful. The roadway width of LTR (only 9 feet) also limits its usefulness, Water depth requirements are given in Table
30.

LTR RAFTING OPERATIONS
Capabilities The LTR can be built in the configurations shown in Table 31. When deciding what type of raft to construct, one must consider the required classification of the raft, the required load space of the raft, and whether or not articulating assemblies will be needed to adapt the raft ramps to the shore conditions which exist at the rafting sites. When some doubt exists as to the need for articulators, always plan to use them.

Assembly times The assembly times for LTRs are shown in Table 31. It is assumed that one combat engineer platoon will be used for construction during daylight hours. These times will increase by 50 percent for construction at night.

EXAMPLE: How much time is required for the construction of a four-ponton, four-bay LTR assembled with articulating assemblies, at night?

SOLUTION: Refer to Table 31. This table states that one platoon can build this raft in 36 minutes during the day. Adding 50 percent for construction at night, one platoon can assemble this raft in 54 minutes.

When planning to load these rafts, it is impor-
Classification of LTRs tant to remember that the roadway width of the Raft classification is based upon the current LTR is only 9 feet.

velocity of the river at the rafting site. Table 31
EXAMPLE: How much load space is availprovides the classification of LTRs. Note that able on a four-ponton, three-bay LTR built with the addition of articulating assemblies will norarticulating assemblies?

really decrease the classification of an LTR.

SOLUTION: Refer to Table 31. A four-ponton, three-bay LTR has 30 feet of available load EXAMPLE: What is the classification of a space.

five-ponton, five-bay LTR constructed without Load space The load space for LTRs is shown in Table 31.

Never load ramps or articulating assemblies.

## Light Tactical Rafts And Bridges

articulating assemblies, if the current velocity at the rafting site is 7 FPS?

SOLUTION: Refer to Table 31. A five-ponton, five-bay LTR constructed without articulators can carry vehicles with an MLC of 14 or less when the river is flowing at a velocity of 7 FPS.

Organization for the Construction of LTRs Rafts are normally constructed using one combat engineer platoon. Table 32 provides a description of the crews required. A description of the duties of each crew is provided below crew begins unloading the half-pontons and Construction of a Four-Ponton, carrying them to the water. Pontons are Three-Bay LTR
unloaded by
This raft can be constructed from one set of LTR and consists of four pontons and three Disconnecting the ponton cradle from the pairs of deck panels with ramps attached at trailer.

Carrying The carrying crew removes the half-pontons from the trailer and carries them to the water.

Once all pontons are in the water, this crew carries the deck panels, filler panels, and curbs from the truck to the assembly site.

each end. The normal sequence of construction Attaching the trailer ramps to the rear of is as follows:
the trailer.

1. Once the platoon is formed into crews and the vehicles are positioned so that they are as Attaching a line to the bottom ponton on the trailer.

close to the water as practical, the carrying Ponton connecting The ponton connecting crew connects the half-pontons at their sterns. Once the half-pontons are connected, this crew delivers the whole pontons to the superstructure placement site as required. After all pontons are delivered, this crew helps to position and connect the deck panels, filler panels, and curbs onto the raft.

Deck panel unloading The deck panel unloading crew removes the tie-down chains and unloads the curbs and filler panels while the pontons are being assembled. This crew then unloads the remaining superstructure with the help of the carrying crew.

shifting.
4. Once the first two full pontons are spaced
correctly, the carrying crew delivers two deck panels to the ponton connecting crew.
The connecting crew places the panels into
position over the two pontons with the male ends of the deck panels facing the far shore.
Fasten these deck panels into place using the
Securing the line to a deadman or similar
launched and connected to form full
5. Place two filler panels between the two
anchorage.
pontons, two of these full pontons are
installed deck panels to ensure that the deck
Pulling the truck forward, allowing the
positioned together by spacer bars. Spacer
panels are properly aligned.
bars are allocated in the LTR set, and are
nested pontons and cradle to slide off the
6. The two connected pontons are now pushed
trailer, down the ramps, to the ground,
used to provide the proper spacing between
away from the shore to make room for the
2. As soon as the nested pontons are removed
pontons and to prevent pontons from
addition of the third ponton, which is
from the trailer, the deck panel unloading crew disconnects the trailer from the truck, removes the tie-down chains, and unloads the curbs and filler panels.
3. As half-pontons are placed in the water, the
ponton connecting crew attaches tag lines to
them and connects the half-pontons, stern to
stern. Once all the half-pontons are
brought in by the ponton connecting crew.
7. Position two deck panels over the second
and third pontons. Then push the three
pontons away from the shore and position the fourth ponton. Add two more deck
panels.
8. The articulators and male ramps are now
added to the near shore end of the raft. If
retaining lugs on the pontons.
articulators are not needed, add the male
disconnects the trailer from the truck, removes the tie-down chains, and unloads the curbs and filler panels.

6.

ramps directly to the fourth pair of deck
panels.
9. Add two filler panels between each pair of
deck panels. Place deck curbs along the deck
bays and short curbs along the ramps.
10. Turn the raft around, using tag lines, so that
the articulators and female ramps can be
added to the other end of the raft.
to the raft in the same manner until four
pontons and four bays are completed.
7. Connect the articulators and male ramps to
the near shore end of the raft. If articulators
are not used, pin the male ramps directly to the deck panels on the near shore ponton.
8. Place two filler panels between each pair of
deck panels and a ramp filler panel between
the ramp panels. Connect deck curbs along
both sides of each deck bay and short curbs
along the ramp panels.
9. Turn the raft around, using tag lines, so that
the articulators and female ramps can be
added to the other end of the raft. Complete
this ramp by adding the short curbs and a
ramp filler panel.
Construction of a Four-Ponton, Four-Bay LTR
This raft can be constructed using one set of
LTR. The normal sequence of construction is
as follows:
1. Establish crews, position vehicles, and
unload the half-pontons as described for the
construction of a four-ponton, three-bay
LTR on page 98.
2. Once the nested pontons are removed from
the trailer, the deck panel unloading crew
ponton away from the shore and connect it
to the second ponton.
Construct two additional bays and add them
3. As half-pontons are-placed in the water, the
ponton connecting crew attaches tag lines to
them and connects the half-pontons, stem to
stern. As the first full ponton is completed, this crew takes it to the assembly site.
4. The carrying crew delivers two deck panels
to the ponton connecting crew. These deck panels are centered on the full ponton, with the male ends toward the far shore, and
connected with the retaining lugs. Two filler panels are added to ensure proper spacing
between the deck panels.
5. Now deliver the second full ponton to the
ponton connecting crew. Center two deck
panels on this ponton and connect them in the same manner as the first. Push the first
of the raft. Connect the female ramps and add the short tiller panel and short curbs to complete the ramp.

Construction of a Five-Ponton, Five-Bay LTR
Two sets of LTR are required to construct this raft. The five-ponton, five-bay LTR is built in exactly the same manner as the four-ponton, four-bay raft except that one additional bay
(one ponton with one pair of deck panels centered upon it) is added prior to construction of the first ramp.

shore to provide room for the placement of the next two pontons. Connect these pontons to the constructed portion of the raft using spacer bars.
3. Add two deck panels. This provides the
fourth bay of the raft.
4. Articulators must be used on a six-ponton,
four-bay raft. Add the male articulator
sections and male ramps to the near shore end of the raft.
5. Add filler panels between each pair of deck
panels and a short filler panel between the ramps. Add deck curbs to both sides of the roadway on the deck bays and ramp curbs on
both sides of the ramp.
6. Turn the raft around using tag lines. Connect
the female articulator assemblies to the end
Construction of a Six-Ponton, Four-Bay LTR
Two sets of LTR are required to construct this
raft which consists of six full pontons supporting four pairs of deck panels, or bays. The sequence for the construction of this raft is as follows:
1. Construct a four-ponton, three-bay raft
(without ramps and articulators).
2. Once four pontons and three bays are
connected, push this raft away from the
Construction of a Six-Ponton, Five-Bay LTR
Two sets of LTR are required to construct this
raft which consists of six full pontons supporting
five pairs of deck panels, or bays. The sequence
for the construction of this raft is as follows:
1. Construct a four-ponton, three-bay raft
(without ramps and articulators).
2. Once four pontons and three bays are
connected push them away from the shore
to provide room for the placement of the
next two pontons. Connect these pontons to the constructed portion of the raft using
spacer bars.
Towlines In slight currents over narrow gaps, rafts may be propelled by the use of towlines. The towlines are attached to each end of the raft and may be operated from either one or both banks of the river. With light loads, personnel may be used to pull the raft. When rafting heavier loads, winches on trucks may be used. Two winches on each bank will provide maximum control and allow for faster crossings.

3. Add two deck panels. This provides the
fourth bay of the raft.
4. Connect two more deck panels. This
provides the fifth bay of the raft.
5. Connect the male ramp section to the near
shore bay. Articulators are not used in
constructing this raft.
6. Position two filler panels between each pair
of deck panels, short filler panels between the ramp panels, deck curbs along both sides
of the roadway deck panels, and short curbs along both sides of the ramp.
7. Turn the raft around using tag lines. Add the
female ramp panels, ramp filler panel, and
short curbs to complete the raft.
Ferry systems The bicycle traveler which is provided in the ferry conversion set will allow a raft to move smoothly along a ferry cable. Using the bicycle traveler, either a trail ferry or a flying ferry may be established.

Propulsion of LTRs Use of outboard motors The 25- or 40-horsepower outboard motor provides an excellent means of maneuvering LTRs. These motors can be attached to the downstream end of the raft's pontons, using the motor brackets which are part of the LTR set.

Normally, four outboard motors will be used to propel an LTR although as few as two can be used in currents up to 5 FPS.

Bridge erection boats One BEB, attached to the downstream side of an LTR, will normally provide sufficient means of propulsion. When attaching the boat to the raft, a timber or some other device must be lashed to the ends of the pontons to provide a surface against which the boat can push.

Trail. The trail ferry principle may be used to propel rafts in rivers where the current velocity exceeds 3 FPS. The ferry cable is stretched across the river and attached to a deadman or some other holdfast. When necessary, the cable may be elevated by passing it over an Aframe erected on each bank. Sag is taken out of the cable using ratchet chain hoists. The bicycle traveler is attached to the cable so that its sheaves roll smoothly over the cable. The hauling line is attached to the grommet, and the maneuver lines to the snatch blocks. On the raft, the hauling line is attached to the upstream end of the center ponton, as shown. The maneuver lines are attached to the gunwales of the outside pontons. The trail ferry is operated placed in midstream. The length of the cable must be at least 1 1/2 times the width of the stream. Floating supports should be used to raise the cable clear of the water. The cable is attached to the center of the raft, and maneuver lines are attached at one end to the cable and at the other end to the gunwales on the outside pontons. As the raft moves from shore to shore, Flying. The flying ferry works along the same principle as the trail ferry. Flying ferries can be used in rivers with currents of 4 FPS or greater. The flying ferry runs along a line attached to an anchor which is placed upstream of the raft. If the current is strongest near one shore, the anchor must be nearer the opposite shore. If the current is uniform, the anchor should be is operated by adjusting the maneuver lines so the raft is turned at an angle with the stream current. The upstream ponton should angle towards the opposite shore. The current pushes against the upstream side of the pontons and forces the raft across the stream. Maximum speed is attained by adjusting the angle of the pontons to about 45 degrees.

during daylight hours. Construction times increase by 50 percent for assembly at night.

it swings in the arc of a circle with the center of the circle at the anchor.

Classification of light tactical bridges The classification of a light tactical bridge is based only upon the current velocity of the river at the bridge site. Table 33 provides the classification of LTR bridges in varying current conditions.

EXAMPLE: How much time is required to construct a 200-foot long light tactical bridge during the day?

SOLUTION: Since the rate of assembly is 150
feet per hour, Assembly time =
200 feet of bridge = 1.33 hours
150 ft/hr Therefore, assembly time during the day would be 1.33 hours or 1 hour 20 minutes.

LTR BRIDGING OPERATIONS
Design of Light Tactical Bridges Capabilities Light tactical bridges are not normally constructed because of their inability to carry heavy loads. When light tactical bridges are constructed, the designer must consider the number of sets needed to construct the bridge, the time needed to assemble the bridge, and the load classification required.

EXAMPLE: What is the classification of a light tactical bridge constructed in a current of 7 FPS? Assume a normal crossing will be conducted.

SOLUTION: Refer to Table 33. The classification of this bridge is MLC 13 (for wheeled and tracked vehicles).

Sets required to construct a light tactical bridge One set of LTR can be used to provide 44 feet of bridge. The number of sets needed to bridge a given gap can be determined using the formula:
Number of sets = Gap (ft)
44
OR
Number of sets = Gap (m)
14
EXAMPLE: How many sets of LTR are needed to construct 150 feet of light tactical bridge?

SOLUTION: Number of sets =
Gap (ft) = 150 = 3.41 sets
44
44
Therefore, four sets are needed to complete this bridge.

Assembly times Light tactical bridges can be constructed at the rate of 150 feet per hour by an experienced unit Construction of Light Tactical Bridges Organization Light tactical bridges are constructed in a normal configuration, each bay providing about
11 feet of normal bridge. When constructing LTR bridges in this manner, the use of three assembly sites is recommended. One assembly site is located at the bridge centerline with the other two sites placed a short distance downstream. Bridges under 100 feet long can normally be built using one combat engineer platoon. Longer bridges may require up to one combat engineer company. The recommended organization of construction crews is provided in Table 34.

the personnel at site 3 will construct one raft
consisting of two normal bays. This raft is
used to close the bridge.
7. In closing the bridge, the near shore end
section is pulled into the shore as far as
possible to allow the final two-bay raft to be
connected. This end section is then pushed
back toward the river into its final position.
Ensure that there is sufficient water to prevent the first pontons from resting on the river bottom.
8. Adjust all bridle lines and make final
corrections to bridge alignment. Tighten all approach guys on the near and far shore.
on one full ponton. Each bay is completed by
adding two filler panels and two deck curbs.
A 32-foot rope bridle line is attached to each
pair of normal bays. The completed rafts are
taken to the bridge connecting crew which attaches each raft to the bridge.
5. The anchorage crew can connect the bridle
line attached to each bay to the completed
overhead cable. The near shore abutment crew assists in maintaining bridge alignment as the construction proceeds.
6. Assembly crews at site 2 continue to
construct rafts until the bridge is completed.
Personnel at site 3 may also construct rafts, if a longer bridge is being built. As a minimum,
Construction sequence
Light tactical bridges are generally constructed in the following sequence:
1. Assembly sites are established, equipment
delivered, and crews organized, as shown on page 102 and in Table 34.
2. As the anchorage crew begins installation of
the anchor cable, the ponton crews unload, launch, and join half-pontons at all three
sites.
3. Crews at site 1 and site 3 begin construction
of the near and far shore end sections, respectively. The near shore end section
consists of five normal bays and one ramp section. The far shore end section is built
with four normal bays and a ramp section.
These end sections should be in place as the
anchorage crew completes its duties.
4. The bridge can now be constructed from
both shores towards the middle. The crews
at site 2 construct rafts consisting of four to
six normal bays. Remember that one normal
bay is simply one pair of deck bays centered
sonnel or water to ease its removal if necessary.

To insert the new ponton, weight it with personnel or water and push or pull it into position.

Remove the weight and fasten the ponton to the gunwales using the retaining lugs. The bridge must be closed to traffic during this removal and replacement process.

Deck Maintenance The decks on LTRs and bridges do not normally require extensive maintenance. The gunwale retaining lugs should be checked periodically to ensure they are in the LOCKED
position and are in serviceable condition.

During periods of heavy traffic, the deck may become littered with mud, dirt, or debris from the vehicles using the bridge or raft. The LTR roadway should be washed periodically to ensure safe operation of the raft or bridge.

float dolly on one side of the torn surface and close the tear by hammering on the other side of the ponton just above and below the tear with the ball end of a ball peen hammer. The hammering action forces the material at the tear together so that the application of a coat of plastic cement will form a watertight joint.

Clean the area around the tear prior to applying the plastic compound.

Hasty repairs can also be made by placing a board over the opening with a piece of impregnated fabric between the wood and the aluminum ponton. Bolt or nail the board over the holes. When impregnated fabric is unavailable, a piece of canvas or gasket material is a satisfactory substitute.

Badly damaged and leaking pontons should be replaced. To avoid breaking a bridge, unfasten all the gunwale retaining lugs which hold the damaged ponton in place. Allow the ponton to float downstream. Weight the ponton with per-
MAINTENANCE OF LTR EQUIPMENT
Maintenance of Pontons Pontons should be checked frequently during rafting and bridging operations. The raft commander is responsible for ensuring that all pontons are serviceable and relatively free of water.

Minor repairs can be made in several ways.

If a hole is found in a ponton, it can be filled with wadded fabric or cloth. The fabric should be soaked with grease or a sealing compound before inserting it into the hole. Once this is done, the fabric should be forced into the hole in the same direction in which the hole was made. Enough material should be left on both sides of the hole to ensure that the hole remains plugged. Rather than use cloth to fill the hole, a tapered wooden plug can also be driven into the hole. The plug should be driven in the same direction from which the puncture occurred.

Short and regular tears above the waterline can be hammered sufficiently to make a temporary watertight seal. First, flatten the dent in the material around the tear. Secondly, hold a

## Chapter 8. Anchorage Of Floating Bridges

All military bridges must be held in position by Each of these factors must be considered some system of anchorage. Anchorage systems when deciding upon the type of anchorage syscan be classified as short-term or long-term.

tem to be installed. Generally, the velocity of Short-term anchorage generally refers to a the river and the river bottom conditions will method of holding a bridge in position for a have the greatest impact upon the type of longlimited period of time. Assault bridges, such as term anchorage system that will be selected for the ribbon bridge, are normally anchored using a given site.

only short-term means. Chapter 4 describes the method of anchoring such bridges, using BEBs.

Basic Design Lines of communications bridges, such as The three basic components of all long-term M4T6 and Class 60 bridges, remain in position anchorage systems include approach guys, an for longer periods of time. For these bridges, upstream anchorage system and a downstream use long-term anchorage systems. This chapter anchorage system.

Approach guys Approach guys are cables which prevent the bridge from being pushed away from the shore as a result of the impact of vehicles driving onto the ramps of the bridge. One approach guy is attached to each side (upstream and downstream) of the first bay of bridge on both ends of the bridge. The other end of each approach guy is secured on the shore, normally using chain picket holdfasts. Place approach guys at approximately a 45-degree angle with the bridge centerline. A minimum of 1/2-inch Improved Plough Steel (IPS) cable should be used for each.

describes the design and construction of these long-term anchorage systems.

Three components of a long-term anchorage system

## Design Of Long-Term Anchorage Systems Basic Considerations The Design Of Any System Of Anchorage Is Influenced By Several Factors, Including

Width of the river

Velocity of the river's current River depth River bottom conditions
Height and slope of riverbanks
Soil conditions
Depth of the groundwater table
Available equipment
Upstream anchorage system The upstream anchorage system is the system which holds the bridge in position against the force of the river's normal current. This system is the bridge's primary anchorage system and its design is, normally, the most critical. There are four types of anchorages which can be used for the purpose of upstream anchorage:

Kedge anchors
Shore guys
Combination of kedge anchors and shore guys
Overhead cable system Although several factors may come into play when determining which of these systems to install, the primary considerations are normally the current velocity and river conditions. Table
35 provides guidelines for the selection of an upstream anchorage system.

Downstream anchorage system The downstream anchorage system protects the floating bridge against reverse currents, tidal conditions, eddies, and high winds or storms which might temporarily alter or reverse the natural flow of the river. Kedge anchors, shore guys, a combination of kedge anchors and shore guys, and overhead cable systems can be used as methods of anchoring the bridge downstream. Once again, the design of downstream anchorage systems can be based upon several factors. Normally, river bottom conditions and the velocity of the expected reverse current will be of primary importance.

Table 36 provides guidelines for
-
downstream anchorage systems.

the design of TYPES OF ANCHORAGE SYSTEMS
Kedge Anchors Planning considerations Kedge anchors lie in the streambed and are secured to bridge bays with anchor lines. They are designed to sink with the stock lying flat and the fluke positioned to dig into the bottom. The kedge anchor depends on the streambed for holding power, and is useful only when the bed is composed of sand, silt, loose rock, or other material into which the fluke can take hold. On hard bottoms, the kedge anchor is useless.

Where the streambed is suitable, anchors of the kedge type can be used as a primary anchorage in low debris currents up to 3 FPS for all heavy floating bridges.

Emplacement Anchors and lines. Normally, the standard
100-pound kedge anchor is used when installing a kedge anchor system. Standard kedge anchors are provided with all heavy floating bridges. To determine the number of anchors needed, refer to Table 35 when installing an upstream anchorage system and Table 36 when constructing a downstream kedge anchor system. If sufficient kedge anchors are not available, expedient anchors can be constructed. Some guidelines

1. Prior to laying the anchors, check to ensure
that the anchor line is attached to the anchor using a fisherman's bend knot (see Appendix
A). Exercise caution to ensure that the stock
of the kedge anchor is at right angles to the
shank and locked with the stock key. This
prevents the anchor from lying flat on the bottom and failing to engage.
2. Anchors may be laid either from a BEB or
from a ponton or raft rigged to a BEB. When laying anchors from a propeller-driven boat,
provided in Appendix D. One-inch manila rope is normally used as anchor lines. One line is attached to each kedge anchor. The length of each line must be at least 10 times the depth of the river.

Laying the anchors. The horizontal distance from the ponton or float to the anchors must be at least 10 times the depth of the water, to control the angle of the shank and prevent the anchor from dragging. The following steps for the construction of expedient anchors are should be taken when laying the anchors:
Shore Guy Anchorage Planning considerations Shore guys are cables attached from the bridge to deadmen or similar holdfasts on the shore. Shore guys can be used as upstream or downstream anchorage systems provided that the maximum anticipated current (or reverse current for downstream systems) does not exceed 3 FPS. Shore guys may be used for any length of floating bridge provided that a
45-degree angle can be maintained between the shore guy and the bridge centerline.

the anchor is usually passed over the bow or gunwale with the boat headed upstream. This decreases the possibility of the line becoming fouled in the propeller.
3. Keep the anchor line neatly coiled so it will
pay out freely. Personnel who cast the
anchors must take care to stay clear of the rope to prevent entanglement and injury.
4. After the anchor has been cast, allow the
boat to drift downstream and apply power to
assist the flukes in setting firmly into the
hold before it is connected to the bridge. If the set anchor holds the BEB stationary when operating at 2,000 revolutions per minute (RPM) in reverse, the anchor will hold its section of the floating bridge. If the anchor fails to hold the stream bottom, it should be retrieved, dropped in another location, and reset.

5. After the anchor is firmly set, move the boat downstream to the bay to which the anchor is to be tied and firmly rig the rope to the streambed. When any anchor is put in the bridge.

water, it should be set to ensure that it will Materials Shore guys normally consist of steel cables attached to deadmen. The cable used for shore guy systems should be 1/2-inch IPS cable or any cable which has a comparable breaking strength. The length of these cables depends primarily upon the length of the bridge and the shore conditions.

Combination Of Kedge Anchors And Shore Guys Planning considerations A combination of kedge anchors and shore guys may be used for upstream or downstream anchorage systems in currents less than or equal to 5 FPS. When constructing a combination system, attach kedge anchors to every float and shore guys to every sixth float. Combination systems can only be used at sites where the river bottom is soft enough to allow the anchors to be set.

bridge and around the balk, and through the balk lugs on M4T6 bridges.
2. Tighten the shore guys that were attached to
the bridge during the bridge assembly just
enough to hold them taut. After bridge completion, tighten the four approach guys
simultaneously to prevent longitudinal movement. Then tighten the shore guys simultaneously to maintain bridge alignment. Shore guys must stay above the water to
prevent whipping and accumulation of debris. If necessary, use an A-frame or some other means of intermediate support to raise the guys clear of the water.
Installation Install combination systems in exactly the manner prescribed for the installation of kedge anchor and shore guy systems. Install the kedge anchors prior to the shore guys so that the

Installation
1. When shore guys are used as the upstream
anchorage system for abridge, they are emplaced as the bridge is constructed. The cable should be unreeled from the shore and passed out along the bridge. If necessary, station one person at every other float to
hold the cable out of the water. The guys are
secured to the lifting eyes on the Class 60
anchor lines are suspended below the shore guys.

Overhead Cable An overhead cable system consists of one or more tower supported cables spanning the river parallel to the bridge. Each end of the overhead cable is secured to the shore, preferably through the use of deadmen. Bridle lines are used to connect each bay of bridge to the overhead cable. The cable functions like the cable used in a suspension bridge, except that in its final working position the cable is inclined toward the bridge because of the force of the current on the bridge.

Planning considerations The overhead cable system can be used as both upstream and downstream anchorage systems. An overhead cable system can hold a heavy floating bridge in currents less than or equal to 11 FPS. The following basic reconnaissance information must be determined in order to design an overhead cable system It is also important to be aware of the sizes and types of cable available for use as an overhead cable and the dimensions and types of materials that are available for use as deadmen.

DESIGN OF AN OVERHEAD CABLE
ANCHORAGE SYSTEM
Table 37 provides the basic information which must be calculated or determined when designing the overhead cable system. An expedient method of design for the overhead cable system is given in Appendix C. If the assumptions upon which this design sequence is based are invalid or if a better understanding of this design sequence is desired, refer to the following paragraphs.

Cable Design Size and number of overhead cables Overhead cable systems may be constructed as one-, two-, or three-cable systems. Single cable systems can be built for bridges as long as 1,200
feet in most cases. Installation of cable spans up to 1,500 feet is possible, but more difficult because of the practical limitations of erection equipment and the cable size and weight. If a cable of sufficient diameter is not available, or if the cable required is too large for the bridle lines and tower fittings, two or three smaller cables may have to be installed using a tower cap adapter.

Use Table 38 to determine the size and number of cables required to support Ribbon, M4T6, and Class 60 bridges. Table 39 provides information for light tactical bridges. It is important to understand that both Table 38 and Table 39 are based upon the use of IPS cable.

If IPS cable is not used, select an appropriate substitute, based upon a comparison of the breaking strength of the available cables with that of the required IPS cable. Table 40 provides the weight and breaking strength of IPS cable as well as several other common cable types.

Use of cable clips Both ends of the overhead cable are normally wrapped around a deadman and secured using cable clips. It is essential that the proper number of clips is correctly applied. To determine the number of clips which must be applied to each end of the overhead cable, use the formula:
Number of clips at each end = (3x CD) + 1
where CD is the diameter of the overhead cable, in inches.

These clips should also be spaced according to the cable size. To determine the correct clip spacing (in inches) use the formula:
Clip spacing (in inches) = (6x CD)
where CD is the diameter of the overhead cable, in inches.

When installing cable clips, the base of each clip should bear against the standing (load carrying) end and the U-bolt should bear against the running (loose end). If clips are installed incorrectly, they will cause shearing, excessive wear, breakage, or slippage of the cable. Always use the correct size cable clip to attain maximum holding power.

Length of the overhead cable In Appendix C, the calculation for the length of the overhead cable (in feet) is given as:
CL = L + 250 feet where CL is the required length of the overhead cable (in feet), and L is the distance between the anchorage towers (in feet) and is given as:
L = (1.1x Gap) + 100 feet.

This formula provides an approximate value for the required length of the overhead cable.

This approximation is based upon the most severe river and bank conditions and is intended for use as a planning figure only.

Normally, there is no need to calculate an exact cable length, but if the designer of a cable system so desires, the formula can be derived from information provided in TM 5-312.

Cable sag The ability of the anchor cable to hold the bridge decreases as the sag in the overhead cable increases. Sag is defined as the distance
(in feet) between the cable and the midpoint of a straight line formed by the two cable supports.

Prior to connection of the bridle lines to the overhead cable, tension is applied to the cable and the initial sag determined. A 2 percent sag
(or less) is desired. Initial sag (in feet) may be computed as:
S = (.02x L)
where S is the initial sag, and L is the distance between the towers.

The distance between the towers (L) is determined as:
L = (1.1 x G) + 100 feet where G is the width of the river, in feet.

An initial sag of 2 percent will usually result in a final sag of 5 to 7 percent once the bridge is connected to the overhead cable.

Tower Design When installing an overhead cable system, Class 60 towers are used to ensure that the master cable remains at least 3 feet above the water level. The tower components are provided with each set of M4T6 and Class 60 and located in the Ribbon Bridge Supplemental Set. The tower assembly is made up of a tower base, a pivot unit, six tower sections, a tower cap, a cap adapter, and two wire rope slings. If Class 60 towers are not available, Bailey bridge panels can be used to construct an adequate tower. For additional information, see Appendix B.

tem, the tower is located some distance downstream from the bridge centerline. This distance, the Bridge to Tower Offset (O1) can be calculated as follows:
Tower location Distance from the tower to the waterline.

Before erecting the towers, determine exactly where on each shore to place the towers. Both towers are placed an equal distance from the waterline. For planning purposes, determine this distance (A), in feet, by using the formula:
If the Bank Height (BH) is less than or equal to 15 feet then:
O1 = H + 50 feet where His the actual tower height in feet Tower height Required. To determine the size of the tower which must be built, it is first necessary to calculate the required tower height. Because the purpose of the tower is to elevate the overhead cable to a height at least 3 feet above the water level, the formula for the required tower height
(in feet) is:
If the Bank Height (BH) is greater than 15
feet then:
A= LG
2
where L is the distance between towers in feet and G is the river width in feet..

This calculation, basically, centers the two towers on the river.

O1= H+ BH+35feet where H is the actual tower height in feet and BH is the actual bank height in feet.

HR=3ft+S-BH
where HR is the required tower height in feet, S is the initial sag, and BH is the bank height in feet.

Distance from the bridge centerline to the tower. When using an overhead cable system as an upstream anchorage system, the tower is placed some distance upstream from the bridge centerline. Conversely, if the overhead cable system is used as a downstream anchorage sys-
This distance provides a suitable slope for the cable running from the bridge to the tower.

Note. If the near or far shore bank or tower heights differ, this step must be performed separately for each shore.

Because the height of the bank is used in this calculation, determine the required tower height separately for both the near shore and the far shore (if the bank heights of both shores are not the same).

Actual. Once the required tower height (in feet) is calculated, the actual height of each tower (near and far shore) can be determined.

When using the Class 60 tower, it is possible to bolt the tower cap directly to the pivot unit to obtain a tower height of 3 feet, 8 l/4 inches.

This is the minimum possible tower height. The tower height may be increased by adding up to six of the 10-foot, 10-inch tower sections. Table
41 provides a list of available tower heights.

To determine the actual tower height, compare the required tower height to those available tower heights in Table 41. Always construct the smallest tower which has an actual height greater than or equal to the required tower height.

Deadman Design The use of a deadman on each shore is the preferred method of securing the overhead cable(s). These deadmen provide the holding power for the entire overhead cable system. Because of this, accurate deadman design is critical. Construct deadmen using logs, rectangular timber, steel beams, or similar objects, buried in the ground with a guy line or sling attached to the deadman's center. The holding power of a deadman is affected by the frontal bearing area, mean (average) depth, angle of pull, deadman material, and soil conditions.

Available materials The first step in designing a deadman is to identify the dimensions of all available materials. Generally, select the timber with the largest timber face or a log with the greatest diameter. Use the largest dimension of the proposed deadman as the deadman face (Df).

The smaller dimension is defined as the deadman thickness (Dt).

Depth of deadman
To determine the depth that a deadman
should be buried, three rules must be considered
1. There must be at least 1 foot of undisturbed
soil between the ground water level and the
bottom of the deadman. Therefore, the
maximum mean deadman depth (DDmax) is
defined as:
DDmax=GWL-1ft- (Df)
2
where GWL is the depth of the ground water level in feet.

Df is the size of the deadman face in feet, and DDmax is the maximum mean depth of the deadman (the maximum depth that the center of the deadman can be buried) in feet.

2. The minimum mean depth of a deadman is 3
feet. There is a real danger of the deadman being pulled out of the ground at depths of less than 3 feet.

3. The maximum mean depth of a deadman is 7
feet. Beyond this depth, the advantage achieved in holding power is offset by the difficulty in emplacing the deadman.

To determine the actual mean depth of deadman (depth to the center of the deadman), calculate DDmax using the formula given above.

Compare this value to the minimum and maximum values given in rules 2 and 3, and adjust the depth as necessary.

Length of deadman Deadmen are designed to have lengths which enable them to resist the breaking strength of the cable attached to them. The required length and thickness are based on allowable soil bearing with 1 foot of length added to compensate for the width of the cable trench. The formula for the determination of deadman length DL is:
D L= C C + 1
(HP x Df)
where CC is cable capacity (breaking strength)
HP is the required holding power of the deadman.

Df is the deadman face in feet (or log deadmen, use log diameter in feet).

This is the general formula for the determination of the required deadman length in all circumstances. In Appendix C, the values for CC
and HP have been divided by 1,000 for ease of Given that the minimum tower to deadman slope is 1:1, the minimum value for C is therefore described as:
Cmin = H + DD
Since the maximum tower to deadman slope ratio is 1:4 (or 1/4), the maximum value for C is:
Cmax= 4x(H + DD)
If the length to thickness ratio is exceeded, decrease the length requirements. This can be accomplished by one of the following methods:
Place the deadman at any distance from the tower, as long as that distance falls between these minimum and maximum values. Once the deadman is positioned, make a check of the tower to deadman slope to ensure that the actual slope falls between the criteria given (1:1
and 1:4).

Increase the mean depth of deadrnan (DD).

Increase the tower to deadman slope ratio
(the cable should become more horizontal).

Increase the thickness of the deadman by selecting a deadman with a greater thickness or by using two timbers, placed back-toback.

Tower to deadman offset Just as it was necessary to calculate the distance to place the tower upstream from the bridge centerline, it is now necessary to determine the distance to place the deadman upstream from the tower. This distance is called the tower to deadman offset, or O2. To calculate, use the formula:
calculation. Actual breaking strengtns (CC) or For logs:
cables were provided in Table 40 on page 116.

DL must be less than or equal to 5.

The actual holding power of deadmen in loamy diameter soil is provided in Table 42.

Note: Table 42 assumes the deadman will be buried in loamy soil. For rock or hardpan soil, multiply the values in Table 42 by a factor of 5.

For fine-grained or sandy soil, multiply these values by a factor of 1/2.

The tower to deadman slope, used in Table 42, represents an approximation of the slope of the cable running from the tower to the deadman, as shown on page 121. Since this value cannot be accurately measured until the exact location of the deadman is known, an estimation is made. The tower to deadman slope should fall between a 1:1 slope (45 degrees) and a 1:4 slope
(14 degrees). If it is not possible to obtain an accurate estimate, then assume the worst case (1:1) slope.

Tower to deadman distance The actual distance (in feet) between the tower and the deadman can be described by the formula:
O2 = (C x O2 feet)
where O2 feet is a factor determined from Table 43, and C is the tower to deadman distance (in feet).

C= H+DD
slope where H is the actual tower height in feet, DD is the mean depth of deadman in feet, and the slope refers to the tower to deadman slope ratio.

A slightly more accurate means of positioning the deadman is to determine the exact angle at which the deadman should be placed in relationship to the tower (see Table 44) and place the deadman at
(C) along that angle.

the calculated distance The slight difference Deadman thickness After calculating the required length of the deadman, check the thickness of the deadman to ensure that the deadman will not break due to an insufficient length to thickness ratio.

For timber:
DL must be less than or equal to 9.

Df between the two methods is negligible to the extent that the difference will not cause the system to fail.

Bearing plate design The final step is to design a bearing plate for each deadman. Whenever a deadman composed of wood is used, apply a bearing plate to prevent the cable from cutting into the wood. The two types of bearing plates are flat and formed, each with its particular advantages. The flat plate is easily fabricated. The formed bearing plate can be made of a thin piece of steel.

Flat. Given the size of the deadman face and the diameter of the overhead cable, flat bearing plates can be designed using Table 45 on page
1.24.

Formed. Given the size of the deadman face and the diameter of the overhead cable, the dimensions for a formed bearing plate can be determined using Table 46 on page 125.

INSTALLATION OF AN OVERHEAD
CABLE ANCHORAGE SYSTEM
When constructing an overhead cable system to be used as the primary (upstream) anchorage system for a bridge, construct this system at the same time as the bridge. As bridge bays are brought and connected to the bridge, connect them to the overhead cable using bridle lines.

Usually, one engineer platoon has sussicient personnel to construct a complete single cable overhead anchorage system. When practical, the work on the far shore should progress simultaneously with the work on the near shore.

Organization Table 47 on page 125 provides a list of tasks to accomplish when constructing an overhead cable system. A suggested crew size for each task is also given.

in the pivot unit and pin it to the tower base to keep the pivot unit in the base socket.
5. Raise the tower. For taller towers, some
lifting device may be needed. any crane,
M728 combat engineer vehicle, or M88 recovery vehicle can be used.
6. Adjust the tower guy lines as required.
Installing the Overhead Cable
1. Emplace anchor cables by mounting the
cable reel on the near shore and tow the free end of the cable across the river using a BEB. If the stream bottom is hard and
Installation of Deadman
1. Cut deadman to length and attach bearing
plates as specified by the design procedure.
2. When installing a deadman, dig a hole or
trench perpendicular to the cable to be
attached to the deadman. Place the deadman
in this hole. Dig a sloping trench, which has the same slope as the cable, in front of the hole in which the deadman is placed. This
will allow the cable free access to the
deadman as shown on page 120.
Erection of Towers
1. To assemble the anchor tower, anchor the
tower base, rig the guy lines, and provide deadmen or holdfasts for the tower guy lines. Begin installation of the deadman to which
the overhead cable will be attached prior to tower erection.
2. Install tower base plates and chain holdfasts. 3. Connect the pivot unit, the required number
of tower sections (from the tower design), and the tower cap. Bolt the tower cap to the top tower section. The tower cap has a 3-inch saddle which must be aligned to
receive the overhead cable. For multiple
cable systems, ensure that the two-cap adapter with two wire rope slings is attached to the top tower section.
4. Before raising the tower, secure the guy lines
to the tower cap. Take care not to tangle or
foul these guy lines. Place the erection arm
reasonably clear of shelf rocks and snags,
this method is most effective. The use of intermediate floating supports in areas where a large number of potential snags exist
on the river bottom, may be of good use. Care must be taken when using intermediate floats, particularly in rivers with a swift current, to ensure that the boat can overcome the drag developed by towing the cable.
2. Once the cable is ready for attachment to the
deadman, place the cable under the deadman and around it. This reduces the
the clips.
4. Use the cable clips to secure the cable.
Attach these clips above the ground for ease
of tightening and maintenance.
Attachment of Bridle Lines Once the overhead cable is secured, the bridle line crew can begin connecting the bridle lines from each float to the overhead cable. Bridle lines are normally 32-foot-long sections of 1-
inch manila rope and are attached to the pontons in the ponton assembly area. Use bridle line connectors to attach the bridle lines to the overhead cable.

upward and out of the hole. If the cable cuts
into the ground place a log or board under
the cable at the outlet of the sloping trench.
3. Measure and mark the initial sag distance
from the point of support on each tower.
Establish a line of sight between the marks.
Tighten the cable until its lowest point
touches the line of sight. This adjustment must be made before the bridge is connected
to the cable. Tighten cable clips frequently as more strain is placed on the cable when
bridle lines from the floats are attached.
After the cable has been placed in service
and is under tension, tighten the cable clips again to compensate for any decrease in cable diameter caused by the load and
ensure equal distribution of load between

## Chapter 9. Float Bridge Protective Devices

Antiswimmer Net This net is used to stop swimmers or underwater demolition teams from reaching the bridge. It is also useful in stopping submerged mines and attacks by enemy assault boats.

Impact Boom The impact boom is designed to withstand the impact of large natural or man-made debris and to stop the enemy from attacking the bridge by boat.

Floating bridges, particularly those which will remain in place for long periods of time, must be protected against severe weather conditions and enemy destruction. When it is necessary to close a floating bridge to vehicle traffic because of flood conditions or heavy debris, the removal of pontons, floats, or raft sections will reduce the lateral pressure on the bridge. If loss of the bridge is imminent, release one end section and securely anchor the bridge parallel to the shore.

This is the only protective means available in cases of severe weather. The remainder of this chapter deals with methods of protecting floating bridges against enemy sabotage.

PLANNING CONSIDERATIONS
There are, generally, four elements to consider in determining what types of protective devices to install at a given site. These elements include the tactical situation, time, manpower, and materials and equipment. Regardless of the type of system which is installed, it is critical that the bridge and its protective devices are constantly covered by fire. Post security details and holds them responsible for maintaining surveillance on both banks of the river, as well as on the bridge.

TYPES OF PROTECTIVE DEVICES
The enemy may attempt to destroy floating lines of communications bridges in a variety of ways, including air attack, land attack, underwater demolitions teams, floating mines, or assault boats. Supporting units will normally provide some air defense protection and possibly protection against an attack on the bridge by land. It is necessary to construct floating protective devices to prevent waterborne forces from damaging or destroying the bridge. There are three types of floating protective systems:
Tactical Situation This is the most important element in the design of a protective system. Some considerations include
The likelihood of any enemy waterborne attack.

Antimine Boom This device is constructed to stop any mines which are sent down the river by the enemy.

Whether or not the river is controlled by friendly forces on the upstream and/or downstream side of the bridge.

The importance of the bridge in supporting future operations.

The bank and river conditions.

A good understanding of the tactical situation will help in determining the type, number, and proper location of protective devices. As a minimum, protect bridges with antiswimmer nets placed both upstream and downstream from the bridge and an antimine boom placed upstream of the bridge.

Time This is a critical factor in several ways. The amount of time that the bridge must remain in place will definitely impact upon the degree of protection that is required. Additionally, because of the shortage of engineers on the battlefield, only a limited amount of time will be available to construct devices prior to the receipt of another mission. When time is limited, devices should be installed in the following sequence:
Upstream antimine boom. Antiswimmer nets upstream and downstream, placing the one on the enemy's most likely avenue of approach first.

Impact boom upstream (if needed). Impact boom downstream (if needed).
Materials and Equipment There are no available prefabricated or standardized bridge protective devices. Devices must be constructed from materials available at the bridge site and/or from barrier materials which are readily attainable through the supply system.

Manpower The time required to construct a protective system depends largely upon the manpower available. Give consideration not only to the number of personnel needed to construct the system, but also to the size of the force required to maintain and guard the protective system once it is in place. If manpower is limited, construct the system in the same sequence as stated above.

CONSTRUCTION OF PROTECTIVE
SYSTEMS
Basic Design The figure shows a typical protective system.

The antimine boom is placed first, in the most vulnerable position since mines are the simplest method available to the enemy for destroying the bridge. The antimine boom protects the other protective devices, as well as the bridge.

When the antimine boom is completed, the antiswimmer net can be installed. Place this net closest to the bridge and locate it within the fields of fire of the bridge guards. The antiswimmer net is the only device that extends from the surface of the river to the riverbed. Lastly, the impact boom is installed between the antimine boom and the antiswimmer net. Place all three types of barriers across the water at an angle. Locate the end placed farthest upstream on the side of the river where the current is swiftest. When the barriers are placed in this manner, the current will tend to push any debris to one shore for easy collection. The angle of the barrier will also tend to disorient underwater swimmers. Anchor all three types of protective devices in position using an anchor cable held above the surface of the river using intermediate floating supports. Use midstream anchors to supplement the capabilities of the main anchorage cable. An additional benefit of the use of midstream anchors is that if one section of the protective device is cut or damaged, the remainder of the device will remain intact.

Never use the anchorage system which holds the bridge in place to anchor a protective device.

Construction of the Antimine Boom The antimine boom consists of a number of logs, M4T6 balk, or other large floating structures attached to a cable running across the river. Concertina is normally placed along the length of the boom. The M4T6 balk is the best material for constructing the boom because it is simple to thread cable through the lugs and the balk is airtight and fairly massive.

Attaching balk or logs to the boom cable
There are several methods of attaching the
balk or logs to the cable:
1. Attach cable clips to prevent the cable from
slipping through the balk lugs.
2. Thread and loop the cable through the balk
handles.
3. Fasten cables to logs or railroad ties.
Note. Before using timber logs or railroad ties, ensure that the log or railroad tie will float and is not waterlogged.

Other guidelines for construction Build the antimine boom close to the shore.

The weight of the boom will make it difficult to position the boom once it is constructed. A
BEB is the best means available for towing the boom across the river. Once the boom has been positioned, anchor it on both shores using deadmen or some other holdfast. Install adequate anchorage to prevent the boom from floating downstream and damaging the bridge that the boom is intended to protect. Once the antimine boom is installed, inspect it frequently to prevent debris from building up and collapsing the boom.

Construction of an Antiswimmer Net Construct the antiswimmer net by suspending a mesh or net barrier from an anchorage cable to the river bottom. A number of materials may be available to construct the net. The best expedient is the naval antimine net which is available through the supply system. Other expedients include wire mesh (used for reinforcing concrete), chainlink fence, or other types of fencing material such as barbed tape, barbed wire, or concertina. The material used should form a strong net that is not easily cut. The net should not restrict the flow of water or small bits of debris. The antiswimmer net must also be light enough that it can be positioned with little effort. Once the net is constructed or obtained, thread the anchor cable through the net and the intermediate floating supports. Use floating drums as floating supports. Concertina may also be connected to the cable and net to prevent swimmers from climbing over the net.

Position the cable across the river (using a BEB) and anchor it into position. Finally, fully extend the net to the river bottom and anchor the net into position using any available means.

Note. If the net is not firmly affixed to the river bottom, enemy divers can easily go under the net.

Construction of an Impact Boom The impact boom is designed to prevent large floating structures or boats from destroying the bridge. It is constructed by placing a series of floats and cables across the river. The cables absorb the impact of the debris or boat and restrain it until it can be removed or destroyed. Cable size and float spacing can vary. Increasing the size of the cables and the number of floating supports will increase the level of protection for the bridge.

One means of constructing the impact boom is to fabricate booms consisting of four 1-inch cables supported every 78 feet or less by timberframed buoys so that two crisscrossed cables are above the water and two crisscrossed cables are below the water. Construct the buoys as shown in the figure. Prefabricate buoys and attach all cables along the shore and maneuver them into place using a BEB. The buoy design for a given protective system will largely depend upon the materials that are available for construction purposes.

## Chapter 10. Constructing Fixed Span Bridges From Floating Equipment

CONSTRUCTING FIXED SPANS FROM
M4T6 EQUIPMENT
Characteristics of M4T6 Fixed Spans Short freed spans erected with M4T6 components can provide tactical commanders with a rapid means of crossing narrow streams or dry gaps. The M4T6 freed spans can be built to cross gaps from 9 to 39 feet wide, without intermediate supports. Fixed spans over 45 feet long can be assembled using trestles or piers as intermediate supports.

Components of M4T6
The components used for constructing M4T6
fixed spans are the same as those used for assembling M4T6 floating bridges with the exclusion of the pneumatic pontons and their associated saddle assemblies. For a detailed description of these components, refer to Chapter 5.

Capabilities of M4T6 Fixed Bridges The M4T6 fixed spans can be constructed in the configurations shown in Table 48 as single span, unsupported bridges. Any combination of these spans may be built when supported by two or more trestle assemblies. Trestles assemblies can be constructed in Class 60 or Class 100 arrangements.

Design of M4T6 Fixed Bridges Initial design considerations The desired load classification and the width of the gap are the two primary considerations when designing M4T6 freed span bridges. The desired classification is based upon the heaviest vehicle that is expected to cross the bridge.

Determine the width of the gap by running a measuring tape across the gap along the proposed location of the bridge centerline. En-
Initial design Step 1. Determine the required MLC of the bridge. This is normally designated in the mission statement of the operations order.

Step 2. Measure the gap. The gap is measured from firm ground on the near shore to firm ground on the far shore. For prepared abutments, firm ground is measured from the front face of the abutment. For unprepared abutthe field method of determining firm ground, the angle of repose of the soil is assumed to be 45 degrees. If the slope of the banks does not exceed 45 degrees from the horizontal, then firm ground starts at the top of the banks. If the slope of the bank does exceed 45 degrees from the horizontal, then firm ground starts at a distance, H, from the toe of slope which is equal to sure that the tape is run from a position on firm ments, the location of firm ground-depends on the height of the bank at the toe of slope. (See ground on one shore to another firm position the slope and height of the banks and the angle figure on page 134.)
on the other shore. Stake a line into position of repose of the soil on the banks. When using across the gap to mark the measured centerline.

Step 3. The bridge must have a minimum of 3
feet of bearing on both banks. This is a safety setback that is extended on both the near and far shore banks to ensure that the bridge is bearing on firm ground.

Step 4. Add the safety setback to the measured gap width to determine the required bridge length.

Step 5. Determine trestle requirements.

If the required bridge length is 45 feet or less, then a single span bridge may be adequate.

Design a single span M4T6 bridge.

If the required bridge length is greater than 45
feet, intermediate supports must be used. If the required MLC of the bridge is Class 60 or less, design a freed span with a Class 60 trestle arrangement. If the required MLC of the bridge is greater than Class 60, but not greater than Class
100, design a fixed span with a Class 100 trestle arrangement.

above. Select a deck/roadway balk ratio for the span bridge must be used. Refer to the followbridge span length that was selected in step 5.

ing paragraphs for design of multiple span The deck/roadway ratio must provide the rebridges.

quired MLC for a normal crossing. If the Step 7. If the desired load class is available, desired MLC cannot be attained using the complete the design work sheet provided in the selected bridge span length, then a multiple figure on page 137.

Design of M4T6 single span bridges Steps 1-4. Complete steps 1 through 4 on the single span design work sheet provided in the figure on page 137. These steps are completed in the same manner as steps 1 through 4 shown above.

Step 5. After determining the required bridge length, refer to Table 48 on page 135. Select the shortest bridge configuration which is greater than or equal to the required bridge length.

Step 6. Determine the deck/roadway balk ratio for the bridge, refer to Table 48 and the figure Design of M4T6 fixed spans with a Class 60
trestle arrangement Complete the design work sheet provided in the figure on page 138. For steps 1 through 4, see initial design. The remainder of the work sheet is self-explanatory.

Design of M4T6 freed spans with a Class 100
trestle arrangement Complete the design work sheet provided in the figure on page 139. For steps 1 through 4, see initial design. The remainder of the work sheet is self-explanatory.

Step 4. Construct the H-frame, as shown on pages 149 through 156, as appropriate for the span length desired. The stiffeners should be oriented so that the pin retainer clips attached to the stiffeners are facing toward the closest bank of the gap. Ensure that the H-frame balk is placed in the proper stiffener recesses as shown in the sketches. If the H-frame is constructed using erection girders, construct and launch the erection girder as shown on page
141. The H-frame is then built over the gap, resting on the erection girders. If a crane or vehicle with an A-frame is available to launch the H-frame, build the H-frame on flat ground.

Ensure that every balk is pinned at all stiffeners before removing the erection girders or launching the H-frame.

Step 5. Place the curb adapters in the appropriate recesses on the stiffener as shown in Table 50 on page 142.

Construction of Single Span Fixed Bridges Step 1. Site preparation. The construction site must be cleared and leveled enough to assemble the required H-frame for the span.

Step 2. A line should be placed across the gap to mark the bridge centerline.

Step 3. Prepare the abutments and position the abutment sills to receive the ends of the bridge.

To construct adequate abutments, check Table 49 to determine bank soil bearing capacity. If the soil bearing capacity is greater than 7 tons per square foot, the bearing plate can be placed directly on the ground. For soil bearing capacities of 1 ton per square foot or more, the maximum abutment size required is shown below. For detailed sill abutment design, refer to TM 5-312.

Note. Prepared abutments are not required for the M4T6 freed span bridge; however, if adequate abutments are not provided, the stiffeners and bearing plates at the ends of the bridge will sink into the ground.

Step 6. Launch the H-frame using a crane, erection girders, or a truck-mounted A-frame. Install two bearing plates on the underside of both end stiffeners prior to launching the bridge.

Note. This can be done prior to H-frame construction.

Cranes. It is possible to completely balk and launch 15-foot and 23-foot 4-inch spans when a crane is available. Longer spans must be balked after the H-frame is launched. When using a crane, Class 60 chains or wire rope lifting slings are attached to the ninth recesses (left and right) of the centermost stiffeners on the H- frame.

Erection girders. Erection girders can be constructed and used as described previously.

Truck-mounted A-frame. A truck-mounted A-
frame provides an expedient method of launching an H-frame. (See figure at left.)
Step 7. Place the remaining balk on the stiffeners by starting at one side of the bridge and working towards the other side, or by starting at the centerline of the bridge and and working towards both sides. Pin the balk at all stiffeners except the stiffeners on the end of the span. Be sure to lay the reinforcing balk as shown in the sketches of the balk patterns on pages 149
through 156.

Step 8. Add 20 or 22 tapered balk (depending upon the deck width) to each end of the bridge to provide the ramps. Pin the balk in the end stiffeners. Place cover plates over the joint between the end of the bridge and the ramp.

Step 9. Anchor the ends of the bridge to prevent the span from moving.

Construction of multiple span M4T6 bridges using Class 60 trestle arrangements Step 1. Place a line across the gap to mark the bridge centerline.

Step 2. Accurately measure the gap and clearly mark the location for all trestles. Position trestles as shown in the figure at the right. Make provisions for a solid bearing surface for the trestle shoes. It may be necessary to either dig out or fill in the area in which the trestles will be placed.

Step 3. Construct the first trestle assembly as follows:
1. Place the trestle transom on cribbing to raise the trestle approximately 2.5 feet above the ground. This allows sufficient room to attach the trestle shoes.

2. Place a column in each end of the transom so that approximately 3 feet of each column be placed close to the top of the column, the bracing clamps may have to be removed and then replaced below the level of the transom.

This will prevent the bracing struts from interfering with the positioning of the transom.

Step 4. Construct the near shore H-frame IAW
the bridge design and steps 1 through 7 of the single span construction procedure. Omit the stiffener that would be placed over the trestle arrangement, as well as the short or tapered balk that connects into it, when constructing the H-frame.

trestle assembly with the transom placed
about half way up the columns. Attach the
crane's Class 60 chain hooks to stiffener pins
placed in the seventh right and left recesses
of the transom. Attach tag lines to each
trestle shoe, each lifting eye on the transom, and each strut brace.
7. Adjust the bracing clamps so that the
bracing struts form a 45-degree angle with
the transom.
8. Pin the bottom of each bracing strut to a
picket holdfast. Anchor the picket holdfasts
using eight pickets per holdfast.
9. Place curb adapters in the recesses called for
by the roadway width. (See Table 50.)
10. Raise the transom until it is 6 to 9 inches
above the bank height. If the transom must
extends below the transom. This placement
allows the trrestle to be raised with the least
amount of effort and will prevent the trestle
from sliding when raised.
3. Attach the trestle shoes and secure them to
the column using the special wrench
provided.
4. Attach two bracing clamps to each column.
Place the first clamp directly below the
second hole in the top of the column. Place the second clamp directly below the fourth hole from the top of the column.
5. Place a bracing strut in each bracing clamp
and tighten the clamp.
6. Raise the trestle by hand using the bracing
struts, or with a crane. When raising the
trestle assembly by crane, construct the
the end stiffener that is replaced by the trestle assembly transom and the short or tapered balk that connects into the transom, when assembling and launching the Hframe.

Step 8. Add 20 or 22 tapered balk (depending upon the deck width) to each end of the bridge to provide the ramps. Pin the balk in the end stiffeners. Place cover plates over the joint between the end of the bridge and the ramp.

Step 9. Anchor the ends of the bridge to prevent the span from moving.

Step 10. Once the bridge is completed, the trestle transoms may require adjustment to ensure that the bridge is as level as possible. Make these adjustments using a ratchet chain hoist.

Step 5. Construct a second trestle IAW step 3.

Construct this second trestle 15 feet center to center from the first trestle. Connect the two trestles with 22 normal balk to form a Class 60
trestle arrangement. Pin the balk in the first transom assembly. Reconfigure the bracing so the interior strut braces are connected to the adjacent trestle assembly and so the tops of the exterior strut braces do not interfere with traffic on the bridge. Install transverse bracing below the transom if space is available.

Step 6. Construct additional trestles as required by the bridge design IAW steps 3 and 5 above.

Step 7. When the last trestle is erected construct the far shore span IAW steps 1 through 7
of the single span construction procedure. Omit Construction of multiple span M4T6 bridges using Class 100 trestles Step 1. Place a line across the gap to mark the bridge centerline.

Step 2. Accurately measure the gap and clearly mark the location for all trestles. Position trestles as shown on page 147. Make provisions for a solid bearing surface for the trestle shoes.

It may be necessary to either dig out or fill in the area in which the trestles will be placed.

Step 3. Construct the first trestle arrangement as follows:
1. Place the trestle transom on cribbing to raise the trestle approximately 2.5 feet above the ground. This allows sufficient room to attach the trestle shoes.

2. Insert a full column in each end of the transom. Adjust the transom so it is as close to the cribbing as possible to prevent the trestle from sliding when it is raised upright.

3. Attach the trestle shoes and secure them to
the column using the special wrench
provided.
4. Attach two bracing clamps to each column.
Place the first clamps directly below the
second hole in the top of the column. Place the second clamps directly below the fourth
hole from the top of the column.
5. Place a bracing strut in each bracing clamp
and tighten the clamp.
6. Raise the trestle by hand using the bracing
struts, or with a crane. When raising the trestle assembly by crane, construct the trestle assembly with the transom placed
about half way up the columns. Attach the
crane's Class 60 chain hooks to stiffener pins
placed in the seventh right and left recesses
of the transom. Attach tag lines to each
trestle shoe, each lifting eye on the transom,
and each strut brace.
7. Adjust the bracing clamps so that the
bracing struts form a 45-degree angle with
the transom.
8. Pin the bottom of each bracing strut to a
picket holdfast. Anchor the picket holdfasts using eight pickets per holdfast.
9. Place curb adapters in the recesses called for
by the roadway width. (See Table 50.)
10. Raise the transom until it is 6 to 9 inches
below the bank height. If the transom must be placed close to the top of the column, the
bracing clamps may have to be removed and
then replaced below the level of the transom. This will prevent the bracing struts from
interfering with positioning of the transom.
11. Construct a second trestle, using the same
procedures described above. Place this
trestle between 5 and 15 feet from the first. Normally, place the trestles 8 feet 4 inches
(center to center) or 15 feet apart.
12. Connect the two trestle assemblies by adding
11 short or normal balk so that the end lugs
fit into the transom at every other recess. Timbers (12 x 12 inches) can also be used
instead of balk to connect the trestle
assemblies.
13. Reconfigure the bracing so the interior
bracing struts are connected to the adjacent
trestle assembly and so the tops of the
exterior strut braces do not interfere with
the next trestle arrangement 23 feet 4 inches
(center to center) from the first trestle assembly in the previous trestle arrangement.

Note. If only a Class 90 wheeled/70 tracked capacity is required, then the center to center spacing of the first trestle assemblies can be lengthened to 30 feet.

Step 6. Span the gap between trestle arrangements with either 23-foot 4-inch or 30-foot spans, as required by the bridge design. Assemble spans by following steps 3 through 7 of the single span construction procedure. Both of the end stiffeners and the short or tapered balk that connect into them should be omitted from the H-frame. Pin the balk in the stiffener on the

traffic on the bridge.
14. Install transverse bracing below the transom
if space is available.
15. Place a stiffener with two bearing plates at
the midpoints of the balk.
Step 4. Construct the near shore H-frame IAW
the bridge design and steps 1 through 7 of the single span construction procedure. Omit the far shore stiffener and short or tapered balk that connects into it, when
constructing the H-frame.
Step 5. If additional intermediate supports are
required, continue to construct Class 100 trestle
arrangements by following the procedure in step 3 above. Place the first trestle assembly in
Class 100 trestle arrangement only when the second span's balk has been placed into it. Place cover plates at the joint between the two spans.

Anchor the stiffener with cables or chains so that it cannot shift on the trestle arrangement when vehicles cross.

Step 7. Repeat steps 5 and 6 until all of the intermediate supports are completed.

Step 8. Construct the far shore span IAW steps
1 through 7 of the single span construction procedure. Omit the end stiffener that is replaced by the trestle assembly transom and the short or tapered balk that connects into the transom, when assembling and launching the H-frame.

Pin the balk in the stiffener on the Class 100 trestle arrangement only when the final span's balk has been placed into it. Place cover plates at the joint between the two spans. Anchor the stiffener with cables or chains so that it cannot shift on the trestle arrangement when vehicles cross.

Step 9. Add 22 tapered balk to each end of the bridge to provide ramps. Pin the balk in the abutment stiffeners. Place cover plates over the joint between the ends of the bridge and the bridge ramps. Anchor both ends of the bridge to prevent movement.

Step 10. Once the bridge is completed, the trestle transoms may require adjustment to ensure that the bridge is as level as possible.

Make these adjustments using a ratchet chain hoist.

CONSTRUCTING FIXED SPANS FROM
CLASS 60 EQUIPMENT
Characteristics of Class 60 Fixed Spans Short fixed spans erected with Class 60 components can provide tactical commanders with a means of crossing narrow streams or dry gaps. Class 60 fixed spans can be built to cross gaps from 24 to 54 feet wide, without intermediate supports. Fixed spans over 54 feet long can be assembled using trestles or piers as intermediate supports. The roadway width for all Class 60 bridges is 13 feet 6 inches.

feet Initial design Step 1. Determine the required MLC of the bridge. This is normally designated in the mission statement of the operations order.

Step 2. Measure the gap. Step 3. The bridge must have a minimum of 3
feet of bearing on both banks. Add this bearing requirement to the measure gap width to determine the required bridge length. Gap width Near shore bearing
+3 feet Far shore bearing
+3 feet feet Components of Class 60 Equipment The components required to construct Class
60 freed spans are the same as those used to assemble Class 60 floating bridges with the omission of the pneumatic floats and their associated saddle assemblies.

shown in the figure on page 159. Build bridges which do not use ramp panels as an integral part of the bridge span with earthen or timber ramps. If Class 60 ramp panels are available, they can be used to provide ramps for these bridges as well. These ramps will rest completely on the ground and will not extend over the gap.

Step 1. Determine the required classification and the required length of the bridge.

Step 2. Refer to Tables 51 and 52. Select the smallest bridge span from each table which is greater than or equal to the required bridge length. Using both tables ensures that the designer considers both types of single span bridges during the design process.

Required bridge length =
Step 4. If the required bridge length is greater than 56 feet, use at least one trestle assembly. If the required MLC of the bridge is Class 60 or less, design a fixed span with a Class 60 trestle arrangement. IF the required MLC of the bridge is greater than Class 60, but not greater than Class 100, design a fixed span with a Class
100 trestle arrangement.

Design of Fixed Bridges Using Class 60 Equipment Design considerations The desired load classification and the width of the gap are the two primary considerations when designing Class 60 fixed span bridges. The desired classification is based upon the heaviest vehicle expected to cross the bridge. Determine the width of the gap by running a tape measure across the gap along the proposed location of the bridge centerline. Run the tape from a position on firm ground on one shore to another firm position on the other shore. Stake a line into position across the gap, to mark the measured centerline.

Design of Single Span Bridges Using Class 60 Equipment Types of single span fixed bridges There are two types of Class 60 single span bridges. One type uses the bridge's ramp bays as an integral part of the bridge span. Build these bridges in the configurations shown in Table 51 and the figure on page 158. The second type of single span bridge does not use the ramps as part of the bridge span. Construct these bridges as described in Table 52 and Step 3. Determine the classification(s) of the bridge span(s) that were selected in step 2.

Note that for bridge spans longer than 42 feet
10 inches, the classification is based not only on the type span constructed, but also on the actual gap width. This gap width was determined in the initial design.

Step 4. If neither of the single spans selected provide adequate bridge classification, a multiple span bridge using either a Class 60 or Class
100 trestle may be designed. (See the figure on page 161.)
Design of Multiple Span Bridges Using Class 60 Equipment Like single span bridges, two types of multiple span bridges can be designed. In one type, the near and far shore end sections use ramp panels as an integral part of the bridge span. The second type does not. Bridges which do not use ramp panels as an integral part of the bridge span can be built with earthen or timber ramps.

If Class 60 ramp panels are available, they can be used to provide ramps for these bridges as well. These ramps will rest completely on the ground and will not extend over the gap. Refer to the work sheet provided in the figure on page
162 for the design of Class 60 fixed bridges using Class 60 trestle arrangements. Refer to the work sheet provided in the figure on page
164 for the design of Class 60 fixed spans using Class 100 trestle arrangements. For positioning of Class 60 or Class 100 trestle assemblies, refer to the figures on pages 163 and 165, respectively.

the panel pin holes. Take care to ensure that Step 6. Emplace a ramp filler panel, a normal the stringer flanges of the two sections are deck filler panel, and a short deck filler panel.

butted against the outer retainer lugs on the Bolt these filler panels to the deck panels. Bolt trestle transom, so the filler panels can be two normal curbs and four short curbs to the placed without repositioning the deck panels.

outside flanges on the deck.

Construction of Fixed Bridges Using Class 60
Equipment The assembly of all Class 60 bridges is conducted in approximately the same manner. As an example, the assembly procedures for a 75 foot span, assembled with ramp panels as a part of the bridge span, is described below. Two Class 60 trestles are used for intermediate supports.

Step 1. Prior to constructing trestles, accurately measure the site and clearly mark the location for all trestles. Position trestles as shown in the figure on page 160.

Step 2. Construct a Class 60 trestle assembly.

Refer to the construction of M4T6 multiple span bridges using Class 60 trestle arrangements, step 3. Raise the transom so that it is level with the bank.

Step 3. As the trestle is being braced, join a ramp panel to a normal deck panel using two connector beams. Position the male end of the deck panel to face the far shore. It is easier to assemble the decking when the male end of the panel extends over the transom of the trestle.

Step 4. Once the trestle is in place, use the crane to lift the two-panel section constructed in step 3. Place this section so that it runs from the abutment sill to the transom on the trestle.

Take care to ensure that the end of the bottom flange of the panel is about 6 inches beyond the trestle transom so that another panel section can be joined to the first. Engage the sliding retainer assembly to hold the treadway in place on the transom.

Step 5. Construct a second two-panel section, consisting of a ramp panel and a normal deck panel. Place this section across the gap, parallel to the first section. Align the two sections using Step 7. Assemble the second trestle arrangement, positioning it 15 feet from the first trestle
(center to center). When the second trestle is in position, install and secure the trestleto-trestle bracing and ground bracing (using the bracing struts).

Step 8. Next, the crane lifts a normal deck panel and backs onto the completed portion of the bridge. Pin the deck panel to the male end of one of the deck panels which are resting on the first transom. Remove the yoke pin and lower the deck panel onto the second trestle. The male end of this panel should extend approximately 6 inches beyond the second trestle. Removal of the yoke pin provides a hinge action over the transom.

Step 9. Connect and lower another 15foot deck panel to the second transom. Remove the yoke pin to allow hinge action. Place a deck tread filler panel between the deck panels and bolt curbs to each side of the completed section.

Step 10. Construct a third two-panel section, consisting of one ramp panel and one deck panel. This time, the male end of the deck panel is connected to the ramp, so connector beams are not needed. The crane can now lift this twopanel section and back onto the newly constructed portion of the bridge.

Step ll. Pin the two-panel section to one of the deck panels which rests upon the second trestle arrangement. Lower the ramp panel onto the far shore abutment sill.

Step 12. Construct and emplace the final twopanel section. Place one deck filler panel, one short filler panel, and one ramp filler panel.

Add two normal curbs and four short curbs to complete the far shore portion of the bridge.

Step 13. Make final adjustments to the trestle transoms using the ratchet chain hoists, and ensuring that the bridge is as level as possible.

FIXED SPANS CONSTRUCTED FROM LTR
Characteristics of Fixed Spans Constructed from Light Tactical Floating Equipment Expedient means can be used to erect freed bridges from the superstructure components of the LTR. After assembling sections of the bridge on rollers from the roller conveyor set, launch the bridge across the gap to provide up to 38 feet of bridge without intermediate supports. The roadway width of all light tactical bridges is 9 feet.

Capabilities of LTR Fixed Spans Table 55 provides the load classifications of various span lengths which can be built from LTR components.

## Appendix A Knots And Lashings

Knots and lashings are covered in *TM 5-725.* Some of these are of particular application to watermanship and are given below for ease of reference.

Definitions Double sheet bend The standing part of a rope is that end which, because it is fixed or in The double sheet bend has greater holding power than the single sheet use, cannot be worked. In the illustrations given in this appendix, the bend when joining ropes of equal or unequal diameter, joining wet ropes, standing end of the rope is marked "S". The running end is the free end or tying a rope to an eye. It will not slip or draw tight under heavy loads.

with which the knot is tied. The running end of the rope is marked "R" in the illustrations.

Single sheet bend The single sheet bend, also known as the weaver's knot, is used primarily to tie together two ropes of unequal size. This knot will draw tight but will loosen or slip when the lines are slackened.

Round turn and half-hitches The round turn with two half-hitches is the primary means of securing a rope to a post or other anchorage. For greater security, after this knot is tied the running end should be tied to the standing part of the rope with twine. This process is known as "seizing".

Clove hitch The clove hitch is used to fasten a rope to a timber or post. This knot puts little strain on the rope fibers when the rope is put around an object in one continuous direction. This hitch can be tied along any point on a rope. If there is no constant tension on the rope, another loop around the timber (under the center of the clove hitch) will permit a tightening and slackening motion of the rope.

Fisherman's bend The fisherman's bend is an excellent method for attaching a rope to an anchor, a ring, or a rectangular stone. It can also be used to fasten a rope or cable to a ring or post in situations where there will be a slackening and tightening motion in the rope.

Bowline This is the best knot for making a single loop that will not tighten or slip under strain.

Butterfly knot The butterfly knot is used to pull taut a high line or handline, as a tread rope for footbridges, or for other similar installations. This knot provides the capability to tighten a fixed rope when mechanical means are not available.

## Appendix B Airlift Operations

Aircraft Capabilities Table 56 provides the lifting characteristics of US Army helicopters which are capable of lifting float bridging equipment.

## Airlift Equipment

Lifting sling, 15-000 pound The 15,000-pound lifting sling is normally used for the airlift of floating bridge bays and BEBs. This sling has four 23-foot legs, each leg consisting of a 15-foot nylon web sling and a 6-foot chain leg with 64 links. At one end of each nylon leg is a nylon web ring which is used to attach the sling to the aircraft cargo hook. All four sling legs are held together by the nylon web ring. Sling legs may be added or removed, but the total sling capacity will not exceed 15,000 pounds, regardless of the number of legs used.

Drogue parachute The drogue parachute may be either 5 feet or 5 feet 8 inches in diameter. It is used to improve the flight of certain loads, such as ribbon bridge interior bays, and permits them to be flown at higher speeds. Loads requiring a drogue parachute also require a single leg, swivel hook sling to link the parachute to the load.

ing stake. Once this is done, the helicopter can be grounded by connecting the helicopter hook to the grounding wand. The user should never hold the wand closer than 3 inches from the body.

External Air Transport Procedures for the Boat, Bridge Erection, Twin Jet, Aluminum Hull (USCSBMK-1) (BEB-SD)
Applicability This load is suitable for the CH47A, CH47B, CH47C, CH47D, and CH54 at speeds to 80 knots.

Load description Boat, bridge erection twin jet, aluminum hull, USCSBMK-1, LIN
B83582.

Weight: 8,800 pounds.

Static discharge grounding wand The grounding wand, or rod, is designed to protect the user from static electrical shock during helicopter loading operations. Medium and heavy lift helicopters can produce severe or fatal shocks if not grounded when touched. The stored static electrical energy of any helicopter increases with the helicopter weight, low humidity, and amount of debris blown by the rotor system (such as dust, sand, mist, or snow). The grounding rod consists of a hollowed rod with attached grounding cable and clamp on one end and a hook on the other. A grounding stake is also included.

Lineman's 20 kVA gloves are used for additional protection. The grounding stake should be driven firmly into the ground (a minimum of 6 to 8 inches). The cable on the grounding wand should be attached to the ground-

## Preparation Materials

Tape, adhesive, pressure-sensitive, 2-inch wide roll, National Stock Number (NSN) 7510-00-266-5016.

Cord, nylon, Type III, 550 pounds, NSN 4020-00-240-2146.

Tie-down strap,
15-foot, with lead binder and D-ring, NSN
1670-00-937-0217. Cotton webbing, 1/4-inch, NSN 8305-00-368-2411.

Personnel. Two people can rig this load in 10 minutes.
Procedures
1. Place the apex fitting, centered on the engine compartment hatches.
Route outer sling legs (1 and 2) to front lifting eyes (bow) and inner
sling legs (3 and 4) to rear lifting eyes (stern).
2. Loop the chain end of each sling leg (1 and 2) through the clevis
assembly at its corresponding lifting eye and insert link 10 of each chain
in its own grab hook.
3. Loop the chain end of each sling leg (3 and 4) through the clevis
assembly at its corresponding lifting eye and insert link 16 of each chain
in its own grab hook.
4. Secure free-running end of chain with tape. 5. Pull apex fitting up and trace all sling legs to ensure that they are
properly routed.
6. Secure the front sling legs (1 and 2) to the cab with one turn tape. 7. Take up all remaining slack in the sling legs and place apex on engine
compartment hatches.
Small clevis assembly, NSN 1030-00-360-0304(4 each).
Note. The shackle provided with the boat (see TM 5-1940-277-10) may be
used in lieu of the small clevis assembly.
Personnel. Two people can prepare the load in 20 minutes.
Procedures.
1. Safety tie the beach legs, securing the pins on the diving platform.
2. Secure the hydrojet compliment hatches with nylon cord and engine
compartment hatches with a 15-foot, tie-down strap with load binder and D-ring.
3. Safety tie the mast retaining pin.
4. Secure the map locker. 5. Secure all the lights on the mast with tape. 6. Tape all windows and lights on the cab. 7. Ensure that the cab is secured to the floor of the forward compartment
using organic cable tie-down assembly.
8. Attach the four small clevis assemblies to the lifting eyes of the boat.
Hookup
The hookup person stands on engine compartment hatch, near the center.
Notes.
1. When hooked to the aircraft in flight, this load's long axis will be
approximately 75 degrees to the direction of flight.
2. The 15,000-pound capacity sling set may be used to rig this load by
placing link 2 in grab hook for sling legs 1 and 2 and link 26 in grab hook for sling legs 3 and 4.

## Rigging Materials

Tape, adhesive, pressure-sensitive, 2-inch wide roll.

Sling, helicopter, cargo carrying, external (10,000-pound capacity), NSN 1670-01-027-2902.

External Air Transport Procedures for the Ribbon Interior Bridge Bay Applicability This load is suitable for the CH47B, CH47C, CH47D, and CH54.

Note. THIS INFORMATION IS TENTATIVE IN NATURE. IT HAS
NOT BEEN CERTIFIED BY THE DEPARTMENT OF THE ARMY
AIRBORNE BOARD.

## Load Description Bridge, Ribbon Ramp Bay. Weight: 11,700 Pounds. Preparation Materials Load Description Bridge, Ribbon Interior Bay. Weight: 12,000 Pounds. Preparation Materials

Sling, helicopter, cargo carrying, external, 15,000 pound capacity.

Sling, helicopter, cargo carrying, external 15,000-pound capacity.

Four large air delivery clevises, suspension.

Four large air delivery clevises, suspension.

Tape, adhesive, pressure-sensitive, 2-inch width.

Personnel. Two people can rig the load in 15 minutes.

Procedures

Secure all latches in the LOCKED position.
Forward sling legs (2):
- Connect clevis assemblies (2) to lift provisions.
- Loop the chain end of one sling leg around clevis assembly on the forward end of the bridge. Engage link 5 in the grab link.
- Repeat these procedures on the opposite side.
Aft sling legs (2):
- Connect clevis assemblies (2) to lift provisions.
- Loop the chain end of one sling leg around clevis assembly on the forward end of the bridge. Engage link 7 in the grab link.
- Repeat these procedures on the opposite side.
Tape the sling legs to prevent fouling during hookup.
Tape, adhesive, pressure-sensitive, 2-inch width.
Personnel. Two people can rig the load in 3.5 minutes.
Procedures
1. Secure all latches in the LOCKED position.
2. Forward sling legs (2):
- Connect clevis assemblies (2) to lift provisions.
- Loop the chain end of one sling leg around clevis assembly on the forward end of the bridge. Engage link 7 in the grab link.
- Repeat these procedures on the opposite side.
3. Aft sling legs (2):
- Connect clevis assemblies (2) to lift provisions. - Loop the chain end of one sling leg around the clevis assembly on the
forward end of the bridge. Engage link 7 in the grab link.
- Repeat these procedures on the opposite side.
4. Tape the sling legs to prevent fouling during hookup.
5. Proceed with helicopter hookup.'
Proceed with helicopter hookup.

External Air Transport Procedures for the Ribbon Ramp Bay Applicability This load is suitable for the CH47B, CH47C, CH47D, and CH54.

Note. THIS INFORMATION IS TENTATIVE IN NATURE. IT HAS
NOT BEEN CERTIFIED BY THE DEPARTMENT OF THE ARMY AIRBORNE BOARD.

External Air Transport Procedures for an M4t6 Floating Bridge Bay Applicability This load is suitable for the CH46 or CH53/D/E helicopter.

Note. It is recommended that this be a dual-point load to enhance load stability.

Clear lift-off site of sharp obstacles that could damage the pontons if they get dragged along the ground. Clear the site area one bay length forward and aft of the bridge bay and one bay width on each side.

Load description Bay, bridge, floating, aluminum, highway type, deck balk superstructure on pneumatic floats (M4T6).

Weight: 5,000 pounds.

## Preparation Materials

Sling, helicopter, cargo carrying, external, 15,000-pound capacity. Tape, masking, pressure-sensitive, 2-inch width.

Personnel. Two people can rig the load in 15 minutes.

Procedures

Attachment of sling legs to saddle beams:
- Pass each chain inboard of the balk support and around the saddle
beam. Legs should be positioned fore and aft of the interior saddle panels.
- Fasten link 21 of each chain in its grab link to form loops around saddle beam.
- Attach positioning ropes for each leg as shown below.
- Fasten loose chain ends with tape or rope.
To prevent fouling of the sling before hookup, gather all legs together
at the top center of the load and wrap with several turns of tape.
Secure ropes and loose equipment.

Proceed with helicopter hookup.

## Appendix C Expedient Design Of Overhead Anchorage Systems

Assumptions The following design sequence has been prepared as a reference for the design of overhead anchorage systems. (See figure on page 182.) Several assumptions have been made which simplify the standard design procedures. If these assumptions do not apply to a particular situation, or if an increased understanding of the design sequence is desired, refer to Chapter 8.

All calculations are based upon the use of IPS cables.

Deadmen will be constructed using logs or timbers.

Design Data
The following information must be calculated or determined when
designing an overhead cable system:
Cable data
Number of master cables Size of master cable(s) (CD)
Length of the master cable(s) (CL)
Number of clips at each end of the cable Spacing of cable clips
Initial sag (S)

Flat bearing plates will be used on all deadmen.

The depth of the ground water table at the bridge site is greate than 4
feet. Tidal variations or shore conditions do not require that the anchorage towers be placed a significant distance (over 75 feet) from the waterline. Standard Class 60 towers will be used to support the overhead cable.

The designer is able to roughly estimate the tower to deadman slope ratio. See Chapter 8 for further guidance.

Tower data
Actual tower height (H
Near shore
Far shore
Tower waterline distance (A)
Near shore
Far shore
Tower-bridge offset (O1)
Near shore Far shore
Deadman data
Depth of deadman (DD)
Near shore
Far shore
Tower-deadman distance (C)
Near shore
Far shore

Towerd-deadman offset (O2)
Near shore Far shore Deadman face (Df)
Deadman thickness (Dt)
Deadman length (DL)
Near shore Far shore Bearing plate thickness (x) Bearing plate length (y) Bearing plate face (z)
Step 6. Determine initial sag (S) in feet.

S = (.02x L) Where L = the distance between towers in feet S=
Step 7. Determine tower height (H) in feet.

a. HR = 3 feet + S-BH Where HR = the required tower height in feet S = initial sag in feet BH = bank height in feet Note. This calculation must be done for both the near and far shore since bank heights may be different.

b. Determine actual tower height (H). Refer to Table 59 which provides a list of possible tower heights. Compare the required tower height to the possible tower height. Select the smallest possible tower that is greater than or equal to the required height.

Note. If the near and far shore towers are determined to have different heights, steps 8 through 16 must be calculated separately for both near and far shores.

H near shore = H far shore =
Step 8. Determine the distance from each tower to the waterline (A) in feet.

A = L-G

Overhead Cable Design Sequence
Step 1. Determine the size and number of master cables required. Refer
to Table 57 for M4T6, Class 60, and ribbon bridge. Refer to Table 58
for light tactical bridges.
Step 2. Determine the distance between towers (1) in feet.
L = (1.1x G) + 100 feet
Where G = the width of the wet gap in feet.
Step 3. Determine the length of the master cable (CL) in feet.
CL = L + 250 feet
Where L = the distance between towers in feet.
CL =
Note. This is an approximation based upon the most extreme
circumstances.
Step 4. Determine the number of cable clips required to secure one end of
the master cable.
Number of clips = (3x CD) + 1
Where CD = the cable diameter in inches
Number of clips at each end =
Step 5. Determine the spacing of cable clips in inches.
Clip spacing = (6x CD)
Where CD = the cable diameter in inches
Clip spacing =
2
Where L = the distance between towers in feet G = the gap width in feet A near shore = A far shore =
Step 9. Determine the offset from each tower to the bridge's centerline
(01) in feet.

a. If the bank height (BH) is less than or equal to 15 feet, then 01 = H + 50 feet b. If the bank height (BH) is greater than 15 feet, then 01 = H + BH + 35 feet Where H = the actual tower height in feet BH = the bank height in feet
01 near shore =
Step 10. Identify deadman dimensions. Select a deadman from the available timbers and logs. Generally, the timber with the largest timber face/log diameter is selected. The largest timber face of that deadman is defined as Df the deadman face. The thickness of that deadman is defined as Dt the deadman thickness.

Df = Dt =
Step 11. Determine mean depth of deadman (DD) in feet.

a. There must be a minimum of 1 foot of undisturbed soil between the bottom of the deadman and the ground water level (GWL). Therefore the deepest the deadman can go (DDmax) is calculated as:
DDmax = GWL -1 foot- Df Step 14. Determine the tower to deadman distance (C) in feet.

C= H+DD
slope Where H = the actual tower height in feet DD = the mean depth of deadman in feet slope = the tower to deadman slope C near shore = C far shore =
Step 15. Determine the tower to deadman offset (O2) in feet.

02 = (C x 02 feet) Where C = the tower to deadman distance in feet
02 feet = a factor determined from Table 62
02 near shore =
02 far shore =
Step 16. Design a bearing plate for each deadman. Given deadman face
(Df) or log diameter (d) and the size of the master cable (CD), refer to Table 63 to determine the length, thickness, and face of the deadman bearing plate. x=
y=
z =
2
where Df = the deadman face in feet GWL = depth of ground water level in feet b. The minimum deadman depth is always 3 feet.

c. The maximum deadman depth is always 7 feet.

d. Compare DDmax to these minimum and maximum values to determine the actual mean depth of deadman (DD).

DD near shore =
DD far shore =
Step 12. Determine length of deadman (DL) in feet.

Where CC = the capacity of the anchorage cable in pounds/1,000
from Table 60. HP = required holding power in pounds/1,000 square feet from Table 61.

Df = Deadman face in feet (for log deadman use log diameter (d))
DL near shore =
DL far shore =
Step 13. Check minimum thickness of deadman (Dt) in feet.

For timber: DL must be less than or equal to 9
Dt For logs: DL must be less than or equal to 5.

d

## Appendix D Expedient Anchorages

Trees, stumps, or rocks can serve as natural anchorages for rapid work in the field. Always attach lines near ground level on trees or stumps. Avoid dead or rotten trees as they are likely to snap suddenly when strain is placed on the anchor line. It is always advisable to lash the first tree or stump to a second one, to provide added support. A transom can be placed between two trees to provide a sturdier support. When using rocks as anchorages, examine the rocks carefully to be sure that they are large enough and firmly embedded in the ground. An outcropping of rocks or a heavy boulder buried partially in the ground can serve as a satisfactory anchor.

Multiple wooden pickets The strength of a holdfast can be increased by increasing the area of the lashing is made between the second and the third pickets. If wire rope is picket bearing against the ground. Two or more pickets driven into the used for lashing, only two complete turns are made around each pair of ground, spaced 3 to 6 feet apart and lashed together to distribute the load, pickets. If neither fiber rope nor wire rope is available for lashing, boards are much stronger than a single picket. To construct the lashing, a clove may be placed from the top of the front picket to the bottom of the second hitch is tied to the top of the first picket with four to six turns around the picket and nailed onto each picket. As pickets are placed farther away first and second pickets, leading from the top of the first picket to the from the front picket, the load to the rear pickets is distributed more bottom of the second. Then the rope is fastened to the second picket with unevenly. Thus, the principal strength of the multiple picket holdfast can a clove hitch just above the turns. To tighten the rope place a stake along be increased by using two or more pickets to form the front group. This the rope and twist it. Then drive the stake into the ground. This distributes increases both the bearing surface against the soil and the breaking the load between the pickets. If more than two pickets are used a similar strength.

Combination holdfasts For heavy loading of an anchorage cable, it is desirable to spread the load over the largest possible area of ground. This can be done by increasing the number of pickets used. Four or five multiple picket holdfasts can be placed parallel to each other with a heavy log resting against the front pickets to forma combination log and picket holdfast. The guy line or anchor sling is fastened to the log which bears against the pickets. The log should bear evenly against all pickets in order to obtain maximum strength. The timber should be carefully selected to withstand the maximum pull on the line without appreciable bending. A steel cross member can be used to form a combination steel picket holdfast.

Steel picket holdfasts A standard steel picket holdfast consists of a steel box plate with nine holes drilled through it and a steel eye welded on the end for attaching a guy line. The pickets are also steel, and are driven through the holes in a way that clinches the pickets in the ground. This holdfast is especially good for anchoring horizontal lines, such as the shore guy on a ponton bridge. Two or more of these units can be used in combination to provide a stronger anchorage. A similar holdfast can be improvised with a chain by driving steel pickets through the chain links in a crisscross pattern. The rear pickets are driven in first to secure the end of the chain and the successive pickets are installed so that there is no slack in the chain between the pickets. A lashed steel picket holdfast consists of steel pickets lashed together with wire rope in the same way as wooden stake picket holdfasts.

As an expedient, any miscellaneous light steel members can be driven into the ground and lashed together with wire rope to form an anchorage.

## Expedient Anchors Bailey Panel Bailey Or Similar Bridge Panels With Teeth Attached Can Provide Greater Half Panel Anchor Is Recommended When A Panel Anchor Is Needed. The

anchor holding capacity than the standard 1OO-pound kedge anchor. The high tensile steel teeth used on the panel should be made in the shape of a teeth on the Bailey anchor are attached to one chord and the anchor line kedge anchor fluke. Care must be taken when casting this anchor as it has is attached to the other chord. A half panel anchor provides consistent a tendency to turn upside down.

holding power and is easier to handle than a full panel anchor. The Bailey Nonstandard kedge The following rules should serve as a guide when it is necessary to use other than the standard 100-pound kedge anchor:
Given the same size and shape, additional weight adds very little to the holding power of an anchor.

Construction of Expedient Anchor Towers Using Bailey Bridge Panels.

Bailey bridge panels with either crib or expedient footings are excellent for use as an anchor tower. Nonstandard parts used in this type tower can be fabricated in the field. Bailey panels can be used to construct anchor towers of heights up to 70 feet. With high towers, horizontal panels are normally added to the base to give greater stability. The panel sections are secured together by field fabricated U-type bolts which are fitted around the panel corners. A crown is made by welding 1 1/2 inch by 1 l/2 inch angle irons to the top of the tower.

For general use in a wide range of materials, a fluke angle of about 45
degrees gives the greatest holding power. Angle variations, as little as
10 degrees, can result in a change in holding power of 50 percent or more.

The holding power of anchors of the same size varies with the area of the fluke.

## Appendix E Aluminum Floating Footbridge

which is filled with a light cellular plastic material. This renders the ponton relatively unsinkable even when subjected to small arms fire and shell fragments. The ponton has a maximum gross displacement of 650 pounds.

The aluminum floating footbridge provides a standard means of rapidly crossing dismounted infantrymen in support of river crossing operations.

The footbridge is easily hand-erectable and can be used in currents up to
11 FPS. Although the aluminum floating footbridge is no longer authorized in float bridge companies, the US Army is currently considering a proposal to establish TOEs for aluminum footbridge teams. These teams will provide the equipment and technical advice for erecting approximately 472 feet of footbridge, or 100 feet of light vehicle (Class 2)
bridge.

Treadway The aluminum treadway has a walkway width of 1 foot 8 3/4 inches, a depth of 5 1/4 inches, and an effective length of 11 feet 3 inches. The treadway weighs 84 pounds and consists of two parallel aluminum I-beams carrying transverse aluminum channels which support a corrugated aluminum sheet tread. The ends of the I-beams are fitted with spring loaded connectors, male at one end and female at the other, to provide a connection which develops continuous beam action. This serves to distribute the load over several pontons and provides a connection which does not require the insertion of separate connecting pins.

Components Pontons The aluminum ponton is 14 feet long, 2 feet wide, 1 foot 2.5 inches deep at the gunwales and weighs about 100 pounds. The ponton is fabricated from sheet aluminum, reinforced with light aluminum members. It has a false bottom 6 3/4 inches above the true bottom providing a compartment road from which trucks can back up to the center of the inshore side of the assembly area is also desirable. A water depth of no more than 4 feet along the near shore will permit the assembly crew to efficiently work along the shore.

Handrail post The handrail post is a 1 1/4-inch aluminum tube mounted on an aluminum base and fitted at its top, with a cast aluminum attachment to receive a handrail rope. It weighs about 2 pounds and is installed by inserting the base in a receiving socket in the treadway channel and rotating the post 180 degrees to lock it in position.

Transportation One set of aluminum floating footbridge can be transported using two standard 2 l/2-ton cargo trucks and two trailers with a 2 l/2-ton capacity.

Ropes and holdfasts Each bridge set includes 1/2-inch manila rope to be used as handrail lines, guy lines, and bridle lines; and two 600-foot reels of 3/8-inch wire rope to be used as anchor cables, and as guys for improvised cable towers.

Also included are 20 cable clips, for fastening the cable; 4 holdfasts, each complete with 9 pickets; and 16 approach posts.

Utilization Aluminum floating footbridge can be configured as a floating footbridge, a light vehicle bridge, or as expedient two- or three-ponton rafts.

Footbridge. This bridge is constructed in a normal configuration with one treadway and one ponton per bay. In currents up to 8 FPS, troops must cross in a single file, at a 2-pace interval. In daylight, the bridge can be used to cross 75 men per minute, at a double time. Under blackout conditions, 25 men can cross per minute, at a quick time. The crossing rates shouId be reduced by 20 percent if the current is greater than 8 FPS.

Assembly times are provided in Table 64.

Considerations for Tactical Employment Site considerations Some considerations for the use of aluminum footbridge include: stream conditions, anchorage requirements, and approach requirements.

Stream conditions. Although the aluminum floating footbridge can be used in currents up to 11 FPS, bridge capabilities are significantly reduced in currents over 8 FPS. A location on a straight reach of uniform width is preferable, since the bridge is easily effected by eddies, cross currents, or river turbulence.

Anchorage. Guy lines are always required to maintain bridge alignment.

Anchor cables are required except in currents less than or equal to 3 FPS. Improvised towers using shears or poles must be constructed and raised to hold the anchor cable above the water when the cable is adjusted to an unloaded sag of 3 percent of the span.

Approaches. Assembly by successive bays is used whenever possible.

Desirable site characteristics are
A location requiring a minimum effort in clearing the approach paths for troops on each shore with a good access road minimizing the carrying distance to the assembly sites.

A clear, relatively smooth near shore assembly area, about 30 by 50 feet, with a 50-foot length parallel to the shore. A near shore approach Rafts. Aluminum footbridge may be used to assemble paddle-propelled rafts for light cargo, light vehicles, and wounded personnel. The expedient two-ponton raft is formed by lashing two pontons side by side, with one treadway placed across them. It will accommodate one wounded man and two paddlemen. The expedient three-ponton raft is formed by lashing three pontons side by side with one treadway across them, and an additional treadway along each side of the center treadway. It will accommodate three wounded men and can be paddled by four men.

Light vehicle (Class 2) bridge. An expedient 100-foot long bridge, which will cross a jeep and trailer combination, can be assembled from one set of aluminum footbridge. The treadways are blocked apart and lashed leaving an open space of 2 feet 4 inches between them. The second bay, and succeeding alternate bays, are assembled with the two-ponton bay downstream and the three-ponton bay upstream. Handrail posts are installed only on the outer beam of each treadway. This bridge may be used in currents not exceeding 5 FPS.

Construction of Aluminum Footbridge Assemble aluminum floating footbridge by successive bays whenever the near shore terrain permits a reasonably smooth approach to the water's edge and a near shore assembly site layout like that shown on page 191. A typical organization of assembly details is provided in Table 65. Construction details are further illustrated on page 193.

## Appendix F Access/Egress Roadway System (Aers)

The AERS system is composed of hinged, folding, MLC 70 panels mounted on a dispenser unit. Transport is accomplished using a dedicated standard ribbon bridge truck. The panels are mounted on a dispenser, which can be launched and recovered in the same manner as the bridge bays. The system is designed to provide a stable roadway to (or away from) bridge or raft sites. The roadway provided by one system is approximately 100 feet long with a roadway width of 13.15 feet. Additional missions include temporary stabilization of roadways or other surfaces.

The AERS will be issued to all bridge companies.

Equipment Data
Dimensions of the dispenser with the panel pack installed are provided
below:
Length - 22.2 feet
Width (with retrieval arms stored) - 10,5 feet
Width (with retrieval arms extended) -14.8 feet
Height (with upper beam horizontal) -6.15 feet
Height (with upper beam rotated to its maximum vertical position) - 13.5 feet
Weight -10,970 pounds

tying down the first panel with pins and a cable, then pulling the panels off as the truck moves away. If additional lengths are required, they may be hinged together or overlapped.

Deployment For highway transport, the panel pack is aligned parallel to the dispenser. Launching requires that the panels be rotated perpendicular to the dispenser. This is done by setting the dispenser on the ground and then using the boom on the truck to pick up the panel pack, rotate it, and set it back down on the dispenser. Once the dispenser is recovered by the truck, the matting is ready to be emplaced. As an alternative, the panels may be rotated with the dispenser on the truck, but this requires a crane or another truck with a free boom.

Retrieving Retrieval is accomplished with the truck on the matting. Brackets provided with the system are attached to the end panel of the roadway.

Winch controlled cables connected to these brackets lift the panels up and over the sprockets. Excessive amounts of mud must be removed to permit the panels to fold back onto the dispenser. If the matting has been pushed deep into soft soil, it may have to be pulled free by a large vehicle prior to the retrieval operation. Panels that are damaged must be replaced or removed in order for the matting to properly fold onto the dispenser.

Launching Launching is typically performed by pulling the first panels out and having the truck back up over the mat as it is laid. Since the matting is generally used to cover poor soil conditions, this permits the truck to ride on a stable roadway at all times. Launching may also be performed by

## Glossary

MLC Military Load Class
AERS access/egress roadway system
MPS Mild Plough Steel
AR Army regulation
MSR main supply route
AVLB armored vehicle launched bridge
NCO noncommissioned officer
BEB bridge erection boat
NCOIC noncommissioned officer in charge
BEB-SD bridge erection boat, shallow draft
NSN National Stock Number
CFM cubic feet per minute
OIC officer in charge
FM field manual
OMC Outboard Marine Corporation
FPS feet per second
psi pounds per square inch
HP holding power
RPM revolutions per minute
IAW in accordance with
SOP standard operating procedures
IPS Improved Plough Steel
TM technical manual
LTR light tactical raft
TOE Table of Organization and Equipment
MERADCOM Mobility Equipment Research and
Development Command

## References

REQUIRED PUBLICATIONS
Required publications are sources that users must read in order to understand or to comply with TC 5-210.

TM 5-5420-209-12 Operator's and Organizational Maintenance Manual for Improved Float Bridge (Ribbon Bridge) Consisting of Transporter;
Interior Bay Ramp Bay Army Regulation (AR)
AR 385-15 Water Safety Field Manual (FM)
FM 90-13 River Crossing Operations (How to Fight)
Supply Catalogs (SCs)
SC 5420-97-CL-E03 Bridge, Floating Highway, Class 60
SC 5420-97-CL-E15 Bridge Erection Set, Floating Bridge for Class 60 w/Steel Superstructure and Bridge, Floating Aluminum, Highway, Deck Balk Superstructure SC 5420-97-CL-E28 Tool Kit, Bridge, Floating Aluminum, Foot RELATED PUBLICATIONS
Related publications are sources of additional information. They are not required in order to understand TC 5-210.

SC 5420-97-CL-E35 Bridge, Floating Aluminum, Highway, Deck Balk Superstructure Field Manuals (FMs)
FM 5-34 Engineer Field Data SC5420-97-CL-E42 Bridge, Floating Raft Section, Light Tactical SC 5420-97-CL-E51 Supplementary Set, Bridge FM 5-36 Route Reconnaissance and Classification FM 5-277 Bailey Bridge FM 21-20 Physical Fitness Training FM 55-450-1 Army Helicopter External Load Operations PROJECTED PUBLICATIONS
Projected publications are sources of additional information that are scheduled for printing but are not yet available. Upon print, they will be distributed automatically via pinpoint distribution. They may not be obtained from the USA AG Publications Center until indexed in DA
Pamphlet 310-1.

Technical Manuals (TMs)
TM 5-312 Military Freed Bridges TM 5-725 Rigging Training Circular (TC)
TC 5-312 Military Nonstandard Fixed Bridges TM 5-1940-277-10 Operator's Manual for Boat, Bridge Erection, Twin Jet, Aluminum Hull, Model USCSBMK-1

## Index

By Order of the Secretary of the Army:
CARL E. VUONO
General, United States Army Chief of Staff Official:
WILLIAM J. MEEHAN II
Brigadier General, United States Army The Adjutant General

## Distribution :

Active Army, USAR, and ARNG: To be distributed in accordance with DA Form 12-34B, requirements for Military Floating Bridge Equipment(Qty rqr block no. 651).

+ U.S. GOVERNMENT PRINTING OFFICE : 1994 0- 300-421 (02099)