The HIGHLEAD Program: 

Locating and Designing 

Highlead Harvest Units 

by Using Digital Terrain 

Models. 

United States 

Department of 

Agriculture 

Forest Service 

Pacific Northwest 

Research Station 

General Technical 

Report 

PNW-GTR-206 

Roger H. Twito, Stephen E. Reutebuch, and Robert J. McGaughey 

This file was created by scanning the printed publication. 

Text errors identified by the software have been corrected; 

however, some errors may remain. 
Authors ROGER H. TWITO is a research engineer and STEPHEN E. REUTEBUCH and 

ROBERT J. McGAUGHEY are research foresters, Forestry Sciences Laboratory, 

4043 Roosevelt Way, NE, Seattle, Washington 98105. 
Abstract Twito, Roger H.; Reutebuch, Stephen E.; McGaughey, Robert J. 1988. The 

HIGHLEAD program: locating and designing highlead harvest units by using digital 

terrain models. Gen. Tech. Rep. PNW-GTR-206. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Research Station. 21 p. 

PLANS, a software package for integrated timber-harvest planning, uses digital terrain 

models to provide the topographic data needed to fit harvest and transportation designs 

to specific terrain. HIGHLEAD, an integral program in the PLANS package, is used to 

design the timber-harvest units to be yarded by highlead systems. It solves for the 

yarding limits of direct mainline pull to the top of the tower by assuming that the angle of 

pull must be equal to or greater than the slope of the ground. The ground is sampled 

through a system of 18 uniformly spaced corridor profiles that radiate from userselected landing locations and that are extrapolated from the digital terrain model. 

HIGHLEAD permits the planner to reduce the yarding coverage by shortening yarding 

distance on individual corridors or by deleting portions of the yarding circle. Conversely, 

the planner can try to extend the yarding distance on individual corridors by tightlining. 

The algorithm for tightlining is explained as are limitations of the analysis and interpretations on the maximum, safe log load for highlead systems. A guide giving detailed 

operating instructions for the program is available from the authors. 

Keywords: Timber harvest planning, computer programs/programming, logging 

operations analysis/design, road building (forest/logging). 
Contents 1 Introduction

 1 Background 

 3 Previous Analyses of the Highlead System 

 3 The HIGHLEAD Program 

 3 The PLANS DTM 

 4 Preliminary Highlead Setting Design Using DTMs 

 7 Analytical Description of the HIGHLEAD Program 

 7 Direct Yarding Limit 

 7 Blind Lead Algorithm 

 8 Catenary Correction for the Mainline 

 9 Analysis of Tightlining 

13 Examples of Tightlining 

16 Limitations

16 Payload

17 Tightlining

19 Conclusions 

19 Metric Equivalents 

20 Literature Cited 
Introduction Highlead is the harvesting system most frequently used in the Pacific Northwest, yet 

little information helpful to timber-harvest planners has been published on the physical 

limitations of the system. The lack of analytical procedures cannot be explained by an 

indifference on the part of loggers to the physical layout of the highlead harvesting unit. 

Cable loggers appreciate that lift (deflection) is needed not only for skyline logging but 

also for highlead; however, some aspects of high lead yarding make it troublesome to 

analyze. Interactions between the logs hooked to the highlead system and the terrain 

make a mathematical model providing a single, correct solution for the log-moving 

capacity of the system impossible, especially in borderline cases; yet the predominate 

role of highlead yarding makes a valid process for designing highlead units important. A

program providing such a process is included in the PLANS (preliminary logging analysis system package (Twito and others 1987b). The HIGHLEAD program ascertains the 

physical limits of boundaries for units yardable with highlead cable systems. During 

preliminary planning of harvest activities, a planner using this program can rapidly solve 

and compare alternative highlead harvesting patterns. The program includes options for

extending highlead yarding distance through a tightlining technique. The capacity of the

HIGHLEAD program for rapid analyses is partly the result of using stored digital terrain 

models (DTMs). 'These models, also used by other PLANS design and analysis programs, can be produced by digitizing topographic maps (Twito and others 1987a). 

PLANS was developed by the Forest Engineering Systems group of the Pacific Northwest Research Station, USDA Forest Service. 

Background The highlead system is both the most widely used and one of the simplest (fig. 1) cable 

yarding systems in the United States (Studier and Binkley 1974). Unlike skyline cable 

systems, highlead systems have limited lifting capacity. Logs are generally pulled along 

the ground and occasionally attain partial suspension while being yarded with the 

highlead system. Under favorable conditions (fig. 2), a limited amount of lift to overcome 

ground obstacles can be generated by "tightlining." Tightlining is holding tension in the 

haulback line while pulling the turn of logs toward the landing with the mainline. Because of the increased stress this places on the system, tightlining can cause safety 

problems, accelerate wear of equipment, and slow production. For these reasons, the 

planner should try to layout settings that minimize the need for tightlining. When 

irregular terrain and difficult topography make this impossible, analyzing tightlining is 

desirable to ensure that its use will allow yarding without overloading the highlead 

system. 

1 
Figure 1––Highlead logging system. 

2 

Figure 2––Tightlining logs with a highlead system. 
Previous Analyses of the 

Highlead System 

The HIGHLEAD 

Program 

The PLANS DTM 

When laying out the boundary of a highlead setting, the planner should not allow the 

ground to obstruct the line of sight between any point on the setting and the mainline 

block (Kline 1961, Pearce 1960). Although many authors have presented this general 

rule for planners to follow (Conway 1976, Kline 1961, Liley 1983, Pearce 1960, Studier 

and Binkley 1974, Wellburn 1975), few have presented analytical methods for 

designing highlead units. 

Dykstra (1976) describes a computer program for analyzing options in cable logging; it 

includes algorithms to determine the yarding capacity of a highlead system in terms of 

payload1

 and yarding distance. The program constructs ground profiles of highlead 

corridors by using terrain data extracted from a DTM. Dykstra's analysis of highlead 

payload is unique in the literature, but he does caution that the analysis is only an initial 

effort developed because no other analysis was available to meet his immediate research needs. He states that a more rigorous procedure should be developed for 

estimating highlead load capacity and that his program, as presented, should be 

considered experimental. 

Reutebuch and Evison (1984) developed a computer program that determines maximum yarding reach and occurrences of blind lead along a highlead corridor; they did not

attempt an analysis of load capacity. Their program constructs ground profiles of 

highlead corridors from field survey data, from data derived by digitizing single corridors 

drawn on a topographic map, or from a DTM. 

Both of the computer programs mentioned above use a "line-of-sight" algorithm to 

determine occurrences of blind lead. Dykstra defines blind lead as occurring when the 

line of sight between the tailblock and top of the tower is obscured by the ground line of 

the corridor profile. Reutebuch and Evison use a more conservative definition of blind 

lead, however; they define it as occurring whenever the line of sight between a ground 

point along a highlead profile and the top oft the highlead tower is obscured by the 

ground line. The HIGHLEAD program uses a blind lead algorithm slightly different from 

the "line-of-sight" approach; it is more conservative and realistic than that of either 

Dykstra or Reutebuch and Evison and is unique in providing an analytical basis for 

extending the yarding limits via tightlining. 

The HIGHLEAD computer program was developed to provide an operational tool to help 

the planner rapidly develop and evaluate highlead setting boundaries. The program was 

developed on a Hewlett Packard 9020 computer in the HP BASIC 2.0 language.2

Besides the microcomputer, a printer, a graphics plotter, and a digitizer tablet are 

required to execute the program. 

To use the HIGHLEAD program, the planner must first obtain a topographic map of the 

project area and build a DTM of the project area. The MAP program (Twito and others 

1987a) is used to build the DTM. For MAP, the topographic map with the project area 

delineated on it is taped to the digitizer, and each contour line within the area is traced 

with the digitizer cursor. From these contour data, the MAP program generates a 

gridded DTM of the project area and stores it for use with a variety of PLANS programs, 

including HIGHLEAD. 

1

 The maximum weight of logs that can be safely transported to the landing in one yarding cycle. 

2

 Use of a trade name does not imply endorsement or approval of any product by the USDA Forest Service to 

the exclusion of others that may be suitable. 

3 
Preliminary Highlead 

Setting Design Using 

DTMs 

In a typical run of the HIGHLEAD program, the topographic map of the project area, 

with the boundary of DTM coverage marked on it, is taped to the digitizer tablet, and the 

DTM is loaded into the computer. Next, the height of the highlead tower, the height of 

the tailhold, and the maximum yarding distance for the highlead system are entered. 

The planner then marks the location of likely highlead landings on the map. The digitizer 

cursor is positioned over one of the likely landings, and its position (the x-y coordinates) 

is sent to the computer. The program automatically extracts ground profiles for each of 

18 evenly spaced yarding corridors radiating from the landing (fig. 3). 

Figure 3––Layout of the highlead unit used in the HIGHLEAD program. 

For each of the 18 corridors, the HIGHLEAD program computes the maximum yarding 

distance over which the yarding equipment can operate without exceeding the line 

capacity of the yarder and without yarding in a blind lead situation. 

A plan-view plot of the area that can be yarded to the landing is displayed on the 

terminal screen (fig. 4). Next, the planner may choose to modify the yarding boundary 

by changing the yarding distance for individual corridors or by deleting any of the 18 

corridors from the setting. 

4 
Figure 4––Highlead harvest unit plotted from the HIGHLEAD program. 

Changing the yarding distance for a selected corridor--The planner can modify the 

yarding distance corridor by corridor. The number of the corridor to be modified is 

entered, and its profile is plotted immediately on the computer screen. The position of 

the tower and the initial yarding limit are shown on this profile. If the planner wants to 

extend this limit by tightlining, the location of the tailblock must first be established by 

setting a cursor on the terrain point selected for the tailblock. The analysis proceeds, 

and the yarding limit possible with tightlining is shown on the profile with a message 

explaining why tightlining could not be extended beyond the limit shown. 

A planner may, on some corridors, plan for the highlead system not to yard to its 

maximum reach3

 and, consequently, will adjust the yarding limit of those corridors 

3

 Some planners, depending on their objective, are concerned only with establishing access to the timber 

and do not wish to detail their plan to the point of deciding which of several landings that provide yarding 

access to the timber should be used. If a planner wishes to forecast the harvesting costs for a plan and use 

an analytical program like SIMYAR to predict yarding costs, then the harvest boundaries should be delineated as correctly as possible to ensure an accurate analysis. 

5 
Figure 5––Final design of a highlead harvest-unit for transfer to the timber-harvest plan 

6 

inward. This shortening of yarding distance is done by moving a pointer on the terminal 

screen to a constrained yarding limit selected at a position on the corridor profile that is 

inside the maximum yarding limit shown by the program. 

Deleting yarding corridors––The planner may not want the highlead harvest unit to 

extend around a full 3600 circle. The planner may delete those corridors encompassing

terrain not to be included in the setting by typing in the numbers of the corridors to be 

removed. 

Transferring the designed highlead harvest unit to the plan––When the design of a 

unit is completed, HIGHLEAD can produce a map-scale plot of the unit (fig. 5). This 

plotted drawing can be traced onto the topographic map or to an overlay keyed to the 

map (with the aid of digitized transfer points marked 1 and 2) to provide a permanent 

record of the unit design. Both the initial boundary established by direct mainline pull 

and the boundary resulting from any user modifications are shown on the plot with the 

acreage included in each boundary, the average slope of the unit, and the average 

yarding distance.
Analytical 

Description of the 

HIGHLEAD 

Program 

Direct Yarding Limit 

Blind Lead Algorithm 

The HIGHLEAD program calculates and shows the distance out from the landing 

accessible for yarding; this is the yarding limit. A point on the topographic map is picked 

as a promising landing location. When this point is digitized, a network of 18 evenly 

spaced yarding corridors radiating out from the yarder are plotted in plan-view; each 

corridor subtends a 20° arc. This defines the initial yarding limit of the setting. 

This initial yarding limit shows the area from which logs can be pulled directly to the 

landing by the mainline without the lead angle having to be improved via tightlining. The 

pull of the mainline is not obstructed by any intervening ground and tends to pull logs 

across or over the ground rather than into it. Terrain outside the area of direct mainline 

pull is either in a blind lead area or beyond the maximum reach of the yarding system. 

A terrain profile for each corridor is divided (horizontally) into 20 evenly spaced sections

comprised of elevations calculated from the DTM for 21 evenly spaced terrain points. 

The sequence of checking for ground obstructions begins at the terrain point nearest 

the tower and progresses outward to the maximum reach (limited by mainline length) 

specified for the setting. If, for example, the maximum yarding reach of a system is 

specified to be 1 ,000 feet, the resulting terrain points are 50 feet apart (that is, 1000 

+20=50). If the terrain point 50 feet out from the tower does not result in a blind lead 

situation, the next terrain at 100 feet is checked and so forth. When a blind lead situation occurs, the yarding limit is set at the previous terrain point. If no blind lead problems occur in a corridor, the yarding limit is not reached and extends the full length of 

the mainline reach. 

Blind lead has been defined as a condition on those portions of highlead settings where 

a straight line between a log and the top of the highlead tower intersects the ground. It 

can be approximated, after the timber is cut, as areas inside the harvest unit where the 

tower cannot be seen. The HIGHLEAD program calculates the blind lead point in a 

slightly more conservative manner (fig. 6). 

The initial test for highlead feasibility requires that the angle of pull (Ap) be equal to or 

greater than the angle of the ground (AG). The Ap of the choker must be at least parallel 

to the ground or provide a pull that lifts the hooked end of the log from the ground. If the 

angle is less, the log will be pulled into the ground and a blind lead situation will result. 

The analysis for highlead yarding used in the HIGHLEAD program assumes that the 

chokers are fixed to the log at a point 3 feet above the ground. This makes the analysis 

slightly more conservative because the angle from that point to the head block on the 

tower is slightly lower than if the chokers were fixed at the ground line. 

7 
Figure 6––Angles used for determining the yarding limit from direct mainline pull. 

Catenary Correction for 

the Mainline 

8 

The vertical angle measured from the choker hook point to the mainline block is corrected in this analysis for the slope, or sag angle, of a tensioned wire rope. This sag 

angle, described and measured by catenary equations, brings the analysis closer to 

reality. It is shown as ASAG on figure 6, where the magnitude of ASAG is exaggerated 

for clarity. Fully tensioned wire ropes approximate straight lines (rigid links) more closely 

than figure 6 would indicate. The amount of sag for a wire rope tensioned to a safe 

working load (that is, one-third of predicted breaking strength of extra-improved plow 

steel) is dependent solely on the horizontal distance from the log to the tower. Solving 

for the catenary sag angles of a number of different line sizes and spans shows that 

when the lines are assumed fully tensioned, the angle does not change with line size or 

slope but only with horizontal distance. The method we used to solve these sag angles 

required iterative solutions of the transcendental catenary equations presented by 

Carson (1977). The resulting ASAG can be expressed simply as 0.00155° per foot of 

horizontal span distance, or 1.55° at a 1,000-foot horizontal span. This constant is used 

in the HIGHLEAD program and speeds the analysis considerably. 
Analysis of Tightlining 

The correction of 0.00155° per foot is not trivial. Its effect can be duplicated by using the 

standard "Iine-of-sight" algorithm but shortening the highlead tower to an equivalent 

adjusted height. If this were done, the tower would have to be shortened from its actual 

height by over 27 feet at a yarding distance of 1,000 feet, and by over 13 feet at a 

yarding distance of 500 feet. 

Once the initial yarding limits are calculated for 18 corridors, the planner may try 

extending the yarding distance into areas of blind lead by tightlining. The purpose of 

tightlining is to lift the butt rigging high enough that logs can be skidded to the landing 

without plowing into or hanging up on the ground. Tightlining analysis in the HIGHLEAD

program tests the shape of the ground profile to see if the criteria assumed necessary 

for successful tightlining can be met. Figure 7 outlines this tightlining algorithm. 

Figure 7––Flowchart of the tightlining algorithm. 

In general, the algorithm is based on simple, rational assumptions. The results from a 

force-balance analysis of the three tensioned cables that join at the butt rigging are 

used to determine whether too much tension is required in the haulback line to hold the 

butt rigging where the chokers can pull on the logs with sufficient lift to move the load. 

The details on this assumption follow. 

9 
The butt-rigging position establishes the direction of pull on the log. If the butt rigging is 

close to or on the ground, insufficient upward pull is exerted from the chokers to initiate 

log movement. A solution for tightlining requires that a specific and critical position of 

the butt rigging (where the chokers, the mainline, and the haulback line meet), a necessary prerequisite to log movement, be determined. This butt-rigging position depends on

the shape of the profile, the log weight, the coefficient of static friction between the log 

and the ground, and the tension in the various lines. Because log movement can 

typically occur at many combinations of lead and choker tension, many solutions for 

tightlining are possible. The tightlining algorithm used in HIGHLEAD does not solve for 

specific conditions; it only checks whether or not tightlining will succeed. A key assumption in this algorithm is that the butt rigging must be positioned high enough off the 

ground for its lead to provide a direction of choker pull slightly higher than the slope of 

the ground. This position is the lowest point the butt rigging can occupy if tightlining is to 

succeed (fig. 8). 

Figure 8––Position where the butt rigging is initially set when wire rope tensions and the feasibility of 

increasing the yarding reach by tightlining are analyzed. 

The position assigned to the butt rigging is 4 feet off the ground and 20 feet ahead of 

the log,4

 which results in a near-minimal upward pull angle for the chokers that allows 

skidding (moving) the logs. It also provides a discrete location needed for solving the 

forces in the working lines. 

4

 This position permits a reasonably effective upward pull to be exerted on the log(s) by the chokers 30 

feet long (a reasonable choke length for highlead yarding) hooked to a large-diameter log 3 feet (fig. 8) 

above the ground. 

10 
Higher tension in the chokers is required to move the logs when the butt rigging is 4 feet 

above the ground than when the butt rigging is higher. It is convenient, however, to set 

a butt-rigging position that is at or near the minimum limit of yarding operability. When 

generous deflection in the profile permits lifting the butt rigging to positions higher than 4 

feet, tightlining becomes easier and success more probable. These results do not 

conflict with the tightlining algorithm because the algorithm's line-tension criteria are 

most easily met when the deflection is great. The deflection for the highlead span is 

greatest when the butt rigging is only 4 feet off the ground. The algorithm will therefore 

approve tightlining when the deflection is ample. Log movement may begin with low 

choker tension and at a butt-rigging position higher than 4 feet off the ground, but this 

would tend to occur because the most efficient angle of choker lead (where minimum 

pull through the chokers will overcome the forces resisting log movement) is generally 

when the butt rigging is higher than 4 feet off the ground (see fig. 9). 

Figure 9––The most efficient angle is the angle of pull whereby a 

minimum tension in the chokers is required to move the log. This 

angle is expressed by β = Arc TAN μ. 

When the coefficient of friction between logs and the ground is between 0.5 and 1.0, the

optimum β angle will range between 26.6° and 45°. If log movement does not occur 

when the butt rigging is higher than 4 feet, the tension on the mainline can be increased. This will pull the butt rigging to a lower position, which is unfavorable to log 

movement, but will put a higher tension in the chokers, which is favorable to log movement. In many instances, the increased tension in the chokers will more than compensate for the less effective pulling angle. Therefore this algorithm, which uses a fixed 

position of the butt rigging, should not negate any feasible tightlining opportunities. 

Conversely, when the butt rigging cannot be held as high as the assumed point because of poor deflection, the haulback and choker tensions will not meet the criteria of 

this tightlining algorithm. Even though this 4-foot-high position of the butt rigging might 

rarely occur, it provides a convenient and reliable method for the analysis of tightlining 

when it is combined with checks on line tension. 

With the butt-rigging position set, the line of action of the force vectors in each of the 

working lines can be established. The mainline pulls from the butt rigging to the headblock on the tower. The haulback line pulls from the butt rigging to the tailblock. The 

drop line, or choker, pulls from the butt rigging to the log. The mainline is assumed fully 

11
tensioned, and the analysis is based on the relation between the tensions required in 

the other two lines and the mainline. Three main assumptions govern the tightlining 

analysis. 

1. Tension in the haulback line cannot exceed one-half of the mainline tension. 

This is based on highlead yarding generally being done with a mainline about twice as 

strong as the haulback line. A typical West Coast highlead yarder will spool a 1-1/4-inch 

mainline, which has a safe working strength of 53,300 pounds, and a 7/8-inch haulback, 

which has a safe working strength of 26,500 pounds. The haulback, in this case, has a 

safe working strength and a cross-sectional area slightly less than one-half of the 

mainline. Although other combinations of main and haulback line can be used, the 

implied two-to-one force ratio is a reasonable planning guideline; the mainline does the 

real work of pulling the logs in, and the haulback is generally needed only to pull the 

mainline, butt rigging, and chokers out into the harvest unit. Even when the haulback line 

must be tensioned during tightlining, it is not practical to allow the tension in the 

haulback to equal the tension in the mainline. If the horizontal component of the tension 

in the mainline does not exceed the horizontal component of the tension in the haulback, no tension will be available in the chokers for hauling in (yarding) logs. 

2. Tension in the drop line (choker) must be at least one-half of the mainline 

tension. This assumption, a corollary of the first, ensures that at least half of the pull 

from the mainline is transmitted into the chokers to pull the log towards the landing. The 

reasons for limiting the haulback tension to less than one-half of the mainline tension 

also apply to requiring the dropline tension to be at least one-half of the mainline 

tension. 

3. Tension is the only force permitted in the lines. This assumption provides a 

necessary restraint on the analysis. Wire ropes can act only as tensile structural members. Any force-balance solution meeting the requirements of static equilibrium by 

assigning a compressive force in a wire rope is automatically rejected. 

Two additional assumptions control tightlining analysis but do not relate to line tensions. 

4. The yarding limit for tightlining cannot move as far out as the tailblock, but is 

limited to the terrain point immediately in front of the tailblock. This assumption is 

necessitated by the tightlining algorithm. If the force vectors to be analyzed for the 

tightlining solution are established with the log at the same terrain point as the tailblock, 

the spatial arrangement invalidates the algorithm because the log and the tailblock 

cannot occupy the same space. Harvest planners should be aware that restricting the 

yarding limit resulting from tightlining to the terrain point in front of the tailblock will not 

necessarily constrain the highlead system from yarding up to the tailblock. 

5. The yarding limit for tightlining cannot be set at a slope distance from the tower

that is beyond the reach of the highlead mainline. This final assumption provides a 

way to ensure that the yarding limit will not be set at a point beyond the reach of the 

mainline. The initial direct-yarding-limit analysis encompassed a circle with a horizontal

radius set equal to the maximum slope-yarding distance of the system. The tightlining 

analysis restricts reach in blind lead areas by imposing a slope-distance constraint on 

the reach of the mainline. 

12 
Examples of 

Tightlining 

Designing to increase yarding distance through tightlining is done profile by profile. The 

planner chooses the profile to be examined for tightlining and then must choose a 

location and rigging height for the tailblock on the profile. This location should be 

selected to take advantage of whatever lift the terrain permits. With these inputs, the 

tightlining analysis proceeds automatically. It begins one terrain point beyond the terrain 

point labeled as the yarding limit, based on direct mainline pull; this is the first terrain 

point where the blind lead situation occurred. The routine analyzes that terrain point for 

tightlining operations. If tightlining criteria are met at that terrain point, the analysis 

moves one more terrain point out from the yarder and repeats the analysis for the new 

point. The example in figure 10 shows tightlining analysis at a point where tightlining 

meets the criteria of the algorithm. 

Figure 10––Profile of a situation where tightlining meets the choker 

and haulback tension requirements of the algorithm. 

The force diagram above the profile indicates that the haulback tension is less than half 

(42 percent) and the choker tension is greater than half (65 percent) of the mainline 

tension, as required. This analysis continues until a terrain point is encountered where 

one or more of the five criteria are not satisfied. When this point is encountered, a 

message is printed at the last terrain point meeting the tightlining criteria. The message 

indicates how far along the profile tightlining is feasible and indicates which criteria were 

violated beyond the displayed yarding limit. 

Figure 11 shows where tightlining cannot extend the yarding limit beyond the blind lead 

point. Here the haulback line is overstressed (at 58 percent of mainline tension). Sufficient tension for yarding can pass from the mainline to the chokers, so only the overstressed haulback prevents tightlining success. In this situation, the blind lead point 

13 
Figure 11––Profile of a situation where the haulback tension is too high to 

meet the requirements of the tightlining algorithm. 

(called the "direct mainline pull yarding limit on the program's output) is also the yarding 

limit with tightlining, which shows that tightlining cannot increase yarding reach on this 

profile. 

Tightlining under the conditions shown in figure 12 is difficult to impossible. Here the 

haulback line is overstressed, and the chokers are understressed. 

Planners using HIGHLEAD learn to recognize whether tightlining will or will not work. 

Straight or convex ground profiles, which are poor for skyline yarding, provide little 

possibility for successful tightlining. The situation above (fig. 12) typifies a tug of war 

between the haulback and mainline, where too little (42 percent) of the mainline's 

tension passes into the drop line and too much (61 percent) into the haulback line. 

Figure 13 shows a situation in which the tail block is positioned on the profile at a point 

where lift through tightlining is impossible. When the algorithm can solve the force 

system only by assigning negative tension to either the chokers or the haulback, a 

message indicating that no lift is possible from tightlining is displayed. Negative tension, 

as defined here, is compression-a force impossible to develop in wire ropes. 

These tightlining examples plotted in profile view show and emphasize that lift (deflection) is as important for highlead yarding as for skyline systems. 

14 
Figure 12––Profile of a situation where the haul back tension is too 

high and the choker tension is too low to meet the requirements of

the tightlining algorithm. 

15 

Figure 13––Profile of a situation where tightlining is impossible 

because the algorithm solved the force triangle by assigning a 

compressive force to one of the cables. 
Limitations Smoothed, uniform ground profiles extracted from the DTM may not analytically restrict

yarding to the extent representative of actual ground conditions and therefore could 

limit the usefulness of the HIGHLEAD program. In actual field conditions, short adverse

pitches, dips, rocks, stump butt swells, and terrain irregularities typically occur to 

impede log movement but are conspicuously missing from extracted profiles. These 

irregularities can become major obstructions for highlead yarding, yet accounting for 

them on timber-harvest plans in a way that is both analytically correct and practical is 

difficult. 

The yarding system can be strained and possibly overtaxed if, when log movement 

begins, the log is pulled immediately into an obstruction. When the log is already 

moving with sufficient velocity, it may be able to push through and obliterate potential 

obstructions. Past logging often shows where skidded logs have pushed or plowed 

through obstructions. Such skidtracks develop a trough that permits easier passage of 

the next logs. Because all potential obstructions do not cause hangups, the field irregularities in the analyses can be partially ignored. 

Payload The HIGHLEAD program does not produce a payload analysis for the yarding corridors 

of the designed harvest unit. This makes the program inconsistent with other cablelogging design programs for skyline yarding systems, which usually include a payload 

analysis. One reason for ignoring payload calculations in the HIGHLEAD algorithm is 

that payload for highlead depends on the coefficient of friction between the log and the 

ground, which in turn depends on several variables beyond the level of complexity 

needed for area planning. Furthermore, maximum physical payload for highlead yarders 

is generally so ample that the actual payload hooked is seldom limited. Other factors, 

such as the number of chokers, the number of logs within reach of the chokers, and log 

size, will normally limit the log turn to a weight less than maximum physical payload. 

The yarding limit determined by the mainline pull angle is therefore the most critical 

variable in planning highlead harvest units. 

Maximum physical payload for highlead yarding can be approximated by assuming a 

coefficient of log-drag friction, which will range between 0.5 and 1.0 for logs with bark on 

bare ground; it will differ with log species and diameter, soil texture and moisture 

content, and slope (Henshaw 1977). If a conservatively high coefficient of log-drag 

friction of 1.0 is assumed, and it is also assumed that the logs are on level ground 

(where slope5

 does not affect the payload) and the choker pull is parallel to the ground 

slope, then when the pull in the choker exceeds the log weight log movement will begin. 

Once movement begins, the magnitude of the log-drag force will be reduced because 

the resistance from kinetic (moving) friction is lower than resistance from static (stationary) friction. This will, in turn, permit a higher proportion of the choker tension to increase the acceleration of the log toward the yarder. The safe working tension of the 

mainline is roughly equivalent to the highlead payload on level ground. The highlead 

payload should be multiplied by the reciprocal of the sine plus the cosine of the groundslope angle when the yarding is being done uphill (for example, the payload is 71 

percent of the safe tension in the mainline on 100-percent ground slopes). 

5 Whether the log is yarded uphill or downhill has a considerable effect on the tension required. For 

example, on a 80-percent slope with a coefficient of friction of 1.0, a 1,406-pound force is needed to begin 

moving a 1,000-pound log uphill. Yarding it downhill would only take a 156-pound force. 

16 
A nominal and realistic payload must be assigned to evaluate cable-yarding costs in 

SIMYAR, the yarding-simulation program in PLANS. Payload is constrained by the pull 

exerted through the mainline drum. Theoretically, the mainline in the HIGHLEAD can be 

any diameter, but from a practical standpoint it is usually between 3/4 and 1-3/8 inches; 

the haulback is about one-half of the weight and strength of the mainline. Table 1 lists 

payloads for HIGHLEAD based on mainline size and pull. The program assumes these 

payloads are being yarded uphill on 1 DO-percent slopes and the accelerating force from 

mainline pull is 1,000 pounds greater than the forces resisting log movement. For 

tightlining, the HIGHLEAD algorithm requires that at least one-half of the tension from 

the mainline be transmitted to the chokers; therefore, the payloads for tightlining are 

based on a choker tension one-half that of the direct mainline tension. 

Table 1--Maximum highlead payloads for various combinations of 

main and haulback lines assuming that (1) the mainlines will be 

stressed to their safe working tension, (2) the coefficient of logdrag friction is 1.0, (3) the logs will be yarded up a 100-percent 

slope, (4) the extra pull exerted through the mainline exceeds the 

resisting forces by 1,000 pounds, and (5) the choker pull exerted 

via tightlining is limited to 

one-half of the choker pull attained by direct highlead yarding 

Tightlining Many loggers prefer to rig highlead yarders as a running skyline (referred to as a 

"Grabinsky") to yard areas where direct highlead yarding is difficult because of poor lift. 

This system (see fig.14) is superior to tightlining with conventional highlead rigging on 

corridors where lift is needed because the haulback line is twice as effective in supplying lift to the butt rigging. This improvement in lift does not further reduce the effectiveness of the mainline for moving the logs to the landing because the additional lift is 

supplied totally by the haulback line. The analysis with HIGHLEAD does not, however, 

address this preferred system. 

17 
Figure 14––Highlead yarder rigged as a Grabinsky skyline. 

For the planner wishing to make exact harvest unit designs that take into account the 

differences between the operating limits of tightlining and Grabinsky yarding, we recommend analyzing the Grabinsky access limits by using the running skyline option 

(SKYTOWER; Twito and others in press) in the PLANS program. Entering a small 

carriage clearance (4 to 6 feet) and payload6

 (1 to 3 kips) will approximate Grabinsky 

requirements. 

6 The actual highlead payload would be heavier than this; with highlead yarding, the log is not suspended 

from the carriage as in skyline systems but is fully supported by the ground. 

18 
Conclusions 

Metric Equivalents

- 

We recommend using the HIGHLEAD tightlining option to determine which areas of the 

harvest unit cannot be accessed by direct highlead pull but relying on the Grabinsky 

skyline to ensure that yarding can be accomplished. Any unit requiring a high percentage of its area to be tightlined should, in fact, be yarded by a Grabinsky, which is easier 

on the equipment and the site than are conventional highlead tightlining operations. 

Another skyline option often used to alleviate blind lead problems is the shotgun (flyer) 

method. This option, even though often used with highlead yarders, is definitely a 

skyline system that can also be analyzed with SKYTOWER. When the yarding is uphill 

with the skyline slopes sufficient to permit outhaul of the carriage by gravity and good 

anchoring available, this option should be considered. 

Cable loggers know that, whether they use a skyline or highlead system, the ability to 

operate depends on the ability to lift the logs. Most of the effort for assuring that needed 

lift is available has been expended in analyzing of skyline yarding systems, even though 

highlead is the predominant yarding system in the Pacific Northwest. This HIGHLEAD 

program, although not the first addressing this subject, is a pioneer in analyzing how the 

coverage can be extended via tightlining. The program works quickly and conveniently 

by using DTM data to arrive at highlead settings well adjusted to the topography. 

1 inch = 2.54 centimeters 

1 foot = 0.3048 meter 

1 pound = 0.4536 kilogram 

1 kip = 453.59 kilograms 

19 
Literature Cited 

20 

Carson, Ward W. 1977. Analysis of the single cable segment. Forest Science. 

 23(2): 238-252. 

Conway, Steve. 1976. Logging practices. San Francisco: Miller-Freeman Publications. 416 p. 

Dykstra, Dennis P. 1976. Timber harvest layout by mathematical and heuristic 

 programming. Corvallis, OR; Oregon State Univerity. 299 p. Ph.D. thesis. 

Henshaw, John R. 1977. A study of the coefficient of drag resistance in yarding 

 logs. Corvallis, OR: Oregon State University. 84 p. M.S. thesis. 

Kline, Robert F. 1961. Economic logging sale layout. In: Pacific Logging Congress 

Loggers Handbook, vol. 21; Portland, OR: Pacific Logging Congress: 

29-31 , 115-125. 

Liley, W.B. 1983. Cable logging handbook. Rotorua, New Zealand: Logging Industry 

 Research Association. 182 p. 

Pearce, J. Kenneth. 1960. Forest engineering handbook. Portland, OR: U.S. Department of the Interior, Bureau of Land Management. 220 p. Available from: Oregon 

State University Bookstore, Corvallis, OR 97331. 

Reutebuch, Stephen E.; Evison, David. C. 1984. The cable hauler planning package: user's guide. FRI Bull. 46. Rotorua, New Zealand: New Zealand Forest Service, Forest Research Institute. 81 p. 

Studier, Donald D.; Binkley, Virgil W. 1974. Cable logging systems. Portland, OR: 

U.S. Department of Agriculture, Forest Service. 205 p. Available from: Oregon 

State University Bookstore, Corvallis, OR 97331. 

Twito, Roger H.; McGaughey, Robert J.; Reutebuch, Stepen E. [In press]. The 

SKYMOBILE and SKYTOWER programs for locating and designing skyline 

harvest units. Gen. Tech. Rep. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Research Station. 

Twito, Roger H.; Mifflin, Ronald W.; McGaughey, Robert J. 1987a. The MAP 

program: building the digital terrain model. Gen. Tech. Rep. PNW-GTR-200. 

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Research Station. 22 p. 

Twito, Roger H.; Reutebuch, Stephen E.; McGaughey, Robert J.; Mann, 

Charles N. 1987b. Preliminary logging analysis system (PLANS): overview. Gen. 

Tech. Rep. PNW-GTR-199. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station. 24 p. 

Wellburn, G.V. 1975. Alternative methods for logging steep slopes in the Nelson 

Forest District of British Columbia. Ottawa, ON: Forest Management Institute. Inf. 

Rep. FMR-X- 76. 57 p. 
Operating Instructions 

and Worked Examples 

An appendix to this report containing step-by-step operating instructions for the 

HIGHLEAD program is available from the Pacific Northwest Research Station. A copy of 

this appendix can be obtained by photocopying this page, filling in the necessary 

information, and sending it to: 

USDA Forest Service 

Pacific Northwest Research Station 

Forestry Sciences Lab 

Forest Engineering Systems 4043 

Roosevelt Way NE 

Seattle, WA 98105 

(206) 442-7814 

This appendix includes an example of designing highlead harvest units and demonstrates many of the options and manipulations available. 

If you wish to receive the PLANS program set--which includes HIGHLEAD--stored on 

diskettes, send five 5-1/4-inch double-sided, double-density, flexible mini discs. 

Please send supplementary material for the HIGHLEAD program to: 

NAME 

ADDRESS 

CITY 

STATE & ZIP CODE 

21 
Twito, Roger H.; Reutebuch, Stephen E.; McGaughey, Robert J. 1988. The HIGHLEAD 

program: locating and designing highlead harvest units by using digital terrain models. 

Gen. Tech. Rep. PNW-GTR-206. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station. 21 p. 

PLANS, a software package for integrated timber-harvest planning, uses digital terrain models to provide 

the topographic data needed to fit harvest and transportation designs to specific terrain. HIGHLEAD, an 

integral program in the PLANS package, is used to design the timber-harvest units to be yarded by 

highlead systems. It solves for the yarding limits of direct mainline pull to the top of the tower by assuming 

that the angle of pull must be equal to or higher than the slope of the ground. The ground is sampled 

through a system of 18 uniformly spaced corridor profiles that radiate from user-selected landing locations 

and that are extrapolated from the digital terrain model. HIGHLEAD permits the planner to reduce the. 

yarding coverage by shortening yarding distance on individual corridors or by deleting portions of the 

yarding circle. Conversely, the planner can try to extend the yarding distance on individual corridors by 

tightlining. The algorithm for tightlining is explained as are limitations of the analysis and interpretations on 

the maximum, safe tog load for highlead systems. A guide giving detailed operating instructions for the 

program is available from the authors. 

Keywords: Timber harvest planning, computer programs/programing, logging operations analysis/design, 

road building (forest/logging). 

The Forest Service of the U.S. Department of 

Agriculture is dedicated to the principle of multiple 

use management of the Nation's forest resources 

for sustained yields of wood, water, forage, wildlife, 

and recreation. Through forestry research, 

cooperation with the States and private forest 

owners, and management of the National Forests 

and National Grasslands, it strives –– as directed by 

Congress –– to provide increasingly greater service to 

a growing Nation. 

The U.S. Department of Agriculture is an Equal 

Opportunity Employer. Applicants for all Department 

programs will be given equal consideration without 

regard to age, race, color, sex, religion, or national 

origin. 

Pacific Northwest Research Station 

319 S.W. Pine St. 

P.O. Box 3890 

Portland, Oregon 97208 
March 1988 

U.S. Department of Agriculture 

Pacific Northwest Research Station

319 S.W. Pine Street 

P.O. Box 3890 

Portland, Oregon 97208 

Official Business 

Penalty for Private Use, $300 

do NOT detach label 

BULK RATE 

POSTAGE + 

FEES PAID 

USDA-FS 

PERMIT No. G-40 
HIGHLEAD Program—Users lnstructions 

EXAMPLE 1: ESTABLISHING THE SETTING BOUNDARY FOR A HIGHLEAD 

UNIT. 

The planner wants to determine the area that can be highlead logged uphill to landing 3 by using a yarder with a 

90-foot tower and a maximum reach of 1,200 feet. 

Firmly tape figure 1 to the digitizer tablet, and tape a sheet of clear acetate film over the map. Carefully mark the 

corners of the DTM unit on the overlay. Use this clear overlay as a scratch pad during development of the logging 

plan. 

To access the HIGHLEAD program, the planner must type: 

LOAD "PLANS/BEGIN:CS80,5", 1 (followed by the EXECUTE key) 

The following list of steps must then be executed to analyze the setting. The inputs and outputs for this example 

(example 1) are given. Slightly different results are expected with each run of this example because of slight 

distortions in the map and differences in positioning the digitizer cursor. 

All prompts printed on the terminal screen have been capitalized in the following examples. 

ENTER A 1 THROUGH 8 TO MATCH YOUR CHOICE. 

Keyboard Input: 3 

comment: All keyboard inputs are completed by pressing the RETURN key. 

........ 

Step 1-2 

ENTER THE DATA FILE NAME FOR THE DESIRED DTM UNIT. 

Keyboard input: EXAMPLE_DTM1 

1 
........ 

Step 1-3 

Softkey input: LOAD ONLY THE SHADED DTM 

comment: In this example, the terrain data for only the shaded DTM unit is loaded. 

Step 1-4 

DIGITIZE THE LOWER LEFT CORNER OF THE DTM UNIT. 

DIGITIZE THE LOWER RIGHT CORNER OF THE DTM UNIT. 

Digitizer input: Center the cursor over the lower left corner of the DTM unit and press any cursor key. 

2 

THE SHADED DTM UNIT IS EXAMPLE_DTM1 --- SELECT THE DESIRED LOADING OPTION 

Center the cursor over the lower right corner of the DTM unit and press any cursor key. 

........ 
. 

3 
4 
........ 

Step 1-5 

HOW TALL IS THE TOWER (FT) ? 

........ 

Step 1-6 

HOW HIGH ABOVE THE GROUND WILL THE TAILBLOCK BE RIGGED (FT) ? 

Step 1-7 

WHAT IS THE MAXIMUM SLOPE YARDING DISTANCE (FT)? 

Step 1-8 

WHAT IS THE LANDING NAME OR NUMBER (UP TO 15 CHARACTERS) ? 

Step 1-9 

DIGITIZE LANDING RD. 1520-3 

5 

........ 

........ 

Keyboard input: 90 

Keyboard input: 2 

comment: The taiIblock will usually be rigged to a stump.

Keyboard input: 1200 

Keyboard input: RD. 1520-3 

Digitizer input: Center the cursor over landing 3 and press any cursor key. 

........ 
........ 

The relative position of the digitizer cursor within the map area is represented by the small flashing

cross on the screen. As the planner moves the cursor, the distance from the current cursor location

and the digitized landing location is displayed. 

The planner should slide the yarding corridor template (distributed with the PLANS program disks) 

under the acetate overlay and carefully center it over the digitized landing. The template can then be 

properly aligned with the aid of the digitizer cursor. Move the digitizer cursor until the small flashing 

cursor is centered over corridor 1 on the terminal screen. Rotate the template until corridor 1 on the 

template is directly under the digitizer cursor crosshair. 

After properly aligning the template, the planner can position the cursor at desired tailholds or yarding 

limits and note the distance along each corridor to such points. 

Softkey input: REMOVE CORRIDORS FROM THE SETTING 

comment: The planner does not want the area defined by corridors 3 through 12 to be yarded to landing 3. 

6 

comment:

Step 1-10 
........ 

Step 1-11 

FIRST CORRIDOR YOU WANT TO REMOVE (1-18)? (PRESS RETURN WHEN DONE) 

Keyboard input: 3

........ 

Step 1-12 

LAST CORRIDOR YOU WANT TO REMOVE (1-18) ? (PRESS RETURN TO REMOVE ONLY #3) 

Keyboard input: 12 

comment: Corridors 3 through 12 are removed in a counter-clockwise direction starting with corridor 3 

and 

 finishing with corridor 128 

........ 

Step 1-13 

FIRST CORRIDOR YOU WANT TO REMOVE (1-18) ? (PRESS RETURN WHEN DONE) 

Keyboard input: RETURN 

comment: Pressing the RETURN key without typing a number signals the program that you are done removing 

 corridors. 

........ 

Step 1-14 

Softkey input: MODIFY THE LENGTH OF ANY CORRIDOR 

........ 

Step 1-15 

WHICH CORRIDOR WOULD YOU LIKE TO ANALYZE (1-18)? (PRESS RETURN WHEN DONE) 

Keyboard input: 16

7 
. 

........ 

Step 1-16 

Softkey input: EXTEND REACH BY TlGHTLINING 

Step 1-17 

POSITION THE VERTICAL LINE USING THE OR THEN PRESS TAILBLOCK 

Digitizer input: Move the digitizer cursor along corridor 16 until it is about 1,000 feet from the landing. 

Keyboard arrow keys: Use the screen cursor-positioning arrows at the top of the keyboard to

move the flashing, vertical line left until it is directly over the small flashing 

cross. The vertical line moves in smaller steps when the SHIFT key is held 

down. 

Softkey input: TAILBLOCK

8 

........ 
........ 

Step 1-18 

WANT TO CHANGE THE TAILBLOCK HEIGHT? 

Softkey input: NO 

Step 1-19 

Softkey input: HARD COPY 

comment: The profile plot of corridor 16 is produced on the printer as shown in figure 2. 

Figure –– Profile plot of corridor 16. 

9 

........ 
........ 

Step 1-20 

Softkey input: DONE WITH PROFILE 

........ 

Step 1-21 

WHICH CORRIDOR WOULD YOU LIKE TO ANALYZE (1-18) ? (PRESS RETURN WHEN DONE) 

Keyboard input: 17 

........ 

Step 1-22 

Softkey input: EXTEND REACH BY TlGHTLINING 

10 
........ 

Step 1-23 

POSITION THE VERTICAL LINE USING THE OR THEN PRESS TAILBLOCK 

Keyboard arrow keys: Use the screen cursor-positioning arrows at the top of the keyboard to move the 

 flashing vertical line left to a point about 1,150 feet from the tower. 

Softkey input: TAILBLOCK

Step 1-24 

WANT TO CHANGE THE TAILBLOCK HEIGHT? 

Softkey input: YES 

comment: The tailblock will be rigged 20 feet above the ground on a tree rather than on a stump. 

Step 1-25 

HOW HIGH ABOVE THE GROUND WILL THE TAILBLOCK BE RIGGED (FT) ? 

Keyboard input: 20 

Step 1-26 

Softkey input: DONE WITH PROFILE 

Step 1-27 

WHICH CORRIDOR WOULD YOU LIKE TO ANALYZE (1-18) ? (PRESS RETURN WHEN DONE) 

Keyboard input: 18 

11 

........ 

........ 

........ 

........ 
Step 1-28 

Softkey input: EXTEND REACH BY TlGHTLINING 

Step 1-29 

POSITION THE VERTICAL LINE USING THE OR THEN PRESS TAILBLOCK 

Keyboard arrow keys: Use the screen cursor-positioning arrows to move the vertical line left to a point 

 about 1,000 feet from the tower. 

Softkey input: TAILBLOCK

Step 1-30 

WANT TO CHANGE THE TAILBLOCK HEIGHT? 

Softkey input: NO 

........ 

Step 1-31 

Softkey Input: DONE WITH PROFILE 

........ 

Step 1-32 

WHICH CORRIDOR WOULD YOU LIKE TO ANALYZE (1-18) ? (PRESS RETURN WHEN DONE) 

Keyboard input: 1 

12 

........ 

........ 
........ 

Step 1-33 

Softkey input: SET SHORTER YARDING LIMIT

comment: The yarding limit will be moved in to better match the limits of corridors 2 and 18. 

........ 

Step 1-34 

POSITION THE VERTICAL LINE USING THE OR THEN PRESS YARDING LIMIT 

Keyboard arrow keys: Use the screen cursor-positioning arrows to move the vertical line left to a point 

 about 850 feet from the left end of the profile. 

Softkey Input: YARDING LIMIT

........ 

Step 1-35 

Softkey input: DONE WITH PROFILE 

........ 

Step 1-36 

WHICH CORRIDOR WOULD YOU LIKE TO ANALYZE (1-18) ? (PRESS RETURN WHEN DONE) 

Keyboard input: RETURN 

comment: The RETURN key is pressed without typing a number to signal the program that the planner has 

 completed the setting design. 

........ 

Step 1-37 

Softkey Input: MARK THE UNIT ON THE BASE MAP 

13 
Step 1-38 

MARK AND DIGITIZE 2 REFERENCE POINTS WITHIN THE DASHED RECTANGLE 

comment: The planner should mark two points on the map overlay that will be used to correctly align the plot

of 

 the setting boundary. 

Digitizer input: Center the cursor over each reference point and press any cursor key. 

........ 

Step 1-39 

LOAD PAPER IN THE PLOTTER--PAPER SIZE AT LEAST 9.7 BY 6.0--THEN PRESS RETURN 

comment: The paper must be a minimum size of 9.7 by 6.0 inches. In this case, an 8-1/2- by 11-inch piece is

 acceptable. 

........ 

14 

........ 
........ 

Step 1-40 

ALIGN THE REFERENCE POINTS ON THE PLOT WITH THOSE YOU MARKED ON THE BASE MAP, THEN 

TRACE THE DESIGN ONTO THE BASE MAP. WHEN YOU ARE ALL DONE, PRESS ALL DONE. 

Softkey input: ALL DONE 

comment:: The planner should remove the setting plot shown in figure 3 from the plotter and transfer 

the 

 boundary to the map. A summary of the setting attributes (fig. 4) is printed on the printer. 
16 

Figure 3–– Plan view of the high lead setting. 
, 

Figure 4–– Highlead setting summary. 

Step 1-41 

Softkey input: DESIGN A NEW HIGHLEAD UNIT

........ 

Step 1-42 

Softkey input: GO TO A DIFFERENT PLANS PROGRAM 

........ 

Step 1-43 

comment: The planner can branch to any of the programs in the PLANS package by pressing the 

appropriate 

 softkey. 

17