Ship transport system

A transport system (10) for transporting a litter carrier (40) from one location onboard a first ship to a second location onboard another ship includes a retractable boom (12) having a stationary member (16) and a telescoping member (18) slidably engaged therein. Boom (12) also includes a hoist unit (28) which is operatively connected through a hoist cable (34) to carrier (40) to cause movement thereof. Carrier (40) includes acoustic rangefinders (50) and contact detectors (52) which are electrically coupled to a control circuit (60) located onboard one of the vessels through internal electrical conductors in hoist cable (34). Rangefinders (50) generate signals indicative of the distance between carrier (40) and a selected one of the ships. Contact detectors (52) provide signals which indicate whether carrier (40) is in transit or has landed onto a ship. Control circuit (60) is operable to receive signals from acoustic rangefinders (50) and contact detectors (52) to compensate the operation of hoist (28) and carrier (40) for the relative motion between the two ships, thereby effecting a smooth transfer of the carrier between the ships.

FIELD OF THE INVENTION 
The present invention relates generally to transport systems and more 
specifically to a transport system for transferring personnel and cargo 
between ships. 
BACKGROUND OF THE INVENTION 
Transferring personnel and cargo from ship to ship or ship to shore has 
always been a difficult procedure because of the inherent motion of the 
ocean. The continuous motion of the water causes complex movements between 
the ships, or between the ship and shore, and thus creates problems when 
it is desired to transfer fragile cargo, such as wounded personnel, from a 
ship. Safe transfer of personnel between ships is particularly important 
for hospital ships where injured individuals must be transferred from a 
transport ship to a hospital ship in high seas. 
Prior litter transport systems for ships have generally comprised a boom 
with a winch line connected to a litter carrier. Smooth take-off and 
landing for those prior systems has been extremely difficult to achieve 
even with skilled litter transport operators. Unless the litter carrier is 
lifted at substantially the peak of the upward movement of the vessel, 
there is a risk that after lift-off, the vessel will move upwardly and 
crash into the bottom of the litter. The same problem occurs in attempting 
to place the litter on the deck of the second receiving vessel, since a 
sudden upward movement of the vessel may cause a jarring impact which may 
damage the litter carrier or the patients. 
SUMMARY OF THE INVENTION 
The present invention described and disclosed herein comprises an improved 
ship personnel and cargo handling system which obviates the disadvantages 
of prior art devices by automatically adjusting the movement of the litter 
carrier to compensate for the relative motion between the litter carrier 
and the unloading and loading vessels. 
More specifically, the present invention comprises a litter handling device 
including a hydraulically controlled hoist connected to a litter carrier. 
The litter carrier includes acoustic rangefinder devices and contact 
detectors mounted on the bottom of the carrier at each of its four 
corners. The rangefinder devices and contact detectors are electrically 
connected to a control circuit onboard the hospital vessel through 
internal conductors located in the hoist cable. The system also includes a 
retractable boom and a motion compensating shock absorber operatively 
coupled to the boom. The control circuit receives signals from the various 
sensors and is responsive thereto to vary the relative motion of the 
litter carrier with respect to the unloading and loading vessels. The 
system thus ensures a relatively smooth transfer of one or more litters to 
and from the hospital ship.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, wherein like reference numerals designate 
like or corresponding parts throughout, FIG. 1 illustrates a litter 
transport system 10 incorporating the present invention. Transport system 
10 comprises a retractable boom 12 which is secured by support members 14 
to the main frame of a hospital ship. Boom 12 includes a stationary member 
16 and a telescoping member 18 slidably engaged in stationary member 16. 
Telescoping member 18 is extended or retracted in stationary member 16 
under the control of an open loop hydraulic system including hydraulic 
cylinders 24 and 26 located on stationary member 16. 
A hoist unit 28 is secured to member 16 and includes a position encoder 30 
and slip rings 32. Slip rings 32 are of conventional design of the type 
commercially available and are provided to couple hoist unit 28 to the 
control system components as described hereinafter with respect to FIG. 2. 
Position encoder 30 is a rotary transducer of conventional design and is 
operable to determine the position and velocity of the litter carrier 
relative to the hospital ship. Hoist 28 controls the movement of a hoist 
line 34. Hoist line 34 includes internal electrical conductors and extends 
between hoist 28 and a litter carrier 40. When thus extended, hoist line 
34 passes through a motion compensating shock absorber 42 mounted on boom 
12. Shock absorber 42 is of conventional design and comprises a hydraulic 
cylinder fitted with a position transducer 62 (FIG. 2) and connected 
through control valves (not shown) to a hydraulic accumulator (not shown). 
Hoist line 34 is then extended over a pulley 44 and through a latch 46 
mounted at the end of telescoping member 18 to a carrier latch 48 
positioned at the top of litter carrier 40. Carrier 40 includes acoustic 
rangefinders 50 and contact detectors 52 which are mounted on the bottom 
of the carrier at each corner. The internal conductors of hoist line 34 
electrically connect acoustic rangefinders 50 and contact detectors 52 
with a control circuit 60 (FIG. 2) through slip rings 32 of hoist unit 28. 
FIG. 2 is an schematic diagram of the litter transport system of the 
present invention. As shown in FIG. 2, the internal conductors of hoist 
line 34 are electrically connected to control circuit 60 located onboard 
the hospital ship. Control circuit 60 is also coupled to and receives an 
input from position transducer 62 and from an operator control panel 64. 
Control panel 64 includes controls for controlling the movement of 
telescoping member 18 between an extended or retracted position and for 
controlling the raising or lowering of carrier 40. Switches and 
corresponding indicators are also provided on control panel 64 for 
activating and deactivating the system and for locking and unlocking latch 
46 (FIG. 1). 
In operation, control panel 64 provides an output signal to control circuit 
60 which is processed with inputs from rangefinders 50, contact detectors 
52 and position transducer 62 to provide a control signal to an amplifier 
65. The amplified control signal is applied to a hydraulic pump 66 which 
is driven by an electric motor 68. Hydraulic pump 66 drives a hydraulic 
motor 70 which in turn controls hoist 28 to effect the transfer of carrier 
40. 
Latching device 46 of FIG. 1 is shown in greater detail in FIG. 3. The 
latch includes a pair of hydraulic cylinders 80 and 82 having operatively 
associated therewith a pair of hook members 84 and 86. When activated, 
cylinders 80, 82 are operative to cause hook members 84, 86 to pivot about 
points 88 and 90 respectively. As best shown in FIG. 1, carrier 40 
includes a rod-shaped member 41 mounted on the top surface thereof. As the 
carrier is moved toward the hospital ship, hook members 84, 86 are 
operated to engage member 41 to thus lock the carrier in place at the end 
of telescoping member 18. 
In operation, when it is desired to transfer patients to a hospital ship 
from a transport ship using the litter transport system, the operator 
first activiates the system by depressing a power switch on control panel 
64. Telescoping member 18 is then extended using the extend/retract 
controls on control panel 64 to thus also extend and position carrier 40 
out over the transport vessel. Hydraulic cylinders 80, 82 are then 
operated to unlock latch 46 and thus permit carrier 40 to be lowered 
toward the deck of the transport vessel. As carrier 40 is positioned above 
the transport vessel, acoustic rangefinders 50 provide a feedback signal 
to control circuit 60 to indicate the altitude of the carrier relative to 
the transport vessel. That signal when received by control circuit 60 is 
operable to vary the rate of descent of carrier 40 to minimize the risk of 
an abrupt landing on the transport vessel. This automatic feedback control 
continues until carrier 40 has landed aboard the transport vessel. Once 
the carrier contacts the deck of the vessel, contact detectors 52 provide 
a feedback signal to control circuit 60 to indicate that the carrier has 
landed. The feedback signal is processed through control circuit 60 to 
place the transport system into a "constant tension" mode. In that mode 
the carrier is released from direct operator control and control circuit 
64 is operative to vary the extent of hoist line displacement to 
compensate for the relative movement of the two ships so that constant 
tension is maintained on hoist line 34. One or more litters are then 
placed on carrier 40 for transport to the hospital ship. Before the 
carrier contacts the deck, the control valve coupling the hydraulic 
cylinder of shock absorber 42 and hydraulic accumulator will have been 
kept closed thus causing the shock absorber 42 to hold a fixed position. 
Once the carrier lands, the control valve is opened causing shock absorber 
42 to thereafter act as a spring to prevent the hoist line from going 
slack. Position transducer 62 is operable to provide a signal to control 
circuit 60 representative of the position of the shock absorber so that if 
the shock absorber is getting too near either end of its stroke, e.g., as 
a result of boat motion, control circuit 60 will operate hoist 28 to 
adjust the amount of hoist line extension, to thus recenter shock absorber 
42. During this "constant tension" mode, position transducer 62 and 
position encoder 30 repetitively measure the hoist line displacement 
changes which will vary with the relative motion between the transport and 
hospital ships. Each of those displacement signals is then stored in 
control circuit 60. Once the litters have been loaded onto carrier 40, the 
operator will activate the appropriate control panel switch to raise 
carrier 40. Control circuit 60 is operative, upon receipt of the lift-off 
signal while in the constant tension mode, to delay the raising of carrier 
40 until the transport vessel has reached a peak in its upward movement, 
i.e., when the hoist line displacement is at a minimum, to thus ensure 
against the transport vessel crashing into the carrier after lift-off. 
During the constant tension mode, as the carrier is rising and falling 
with the motion of the transport vessel, position transducer 62 and 
position encoder 30 detect the amount of hoist line extension as it varies 
from a minimum, when the transport vessel is at a peak relative to the 
boom, to a maximum amount of hoist line displacement, when the transport 
vessel is at its lowest point relative the boom. This memory feature thus 
allows carrier 40 to be lifted from the transport vessel when the 
transport vessel is at or near one of its previously recorded peaks. After 
liftoff, acoustic rangefinders 50 are operative to sense the relative 
motion of carrier 40 and the transport vessel and to signal control 
circuit 60 to vary the rate of ascent of carrier 40 to avoid a collision. 
After liftoff, carrier 40 is raised to its topmost position and carrier 
latch 48 engages with latch 46 to lock the carrier in place at the end of 
telescoping member 18. Once carrier 40 has been locked in place, the 
operator retracts telescoping member 18 to bring carrier 40 over the deck 
of the hospital ship for unloading. When carrier 40 is positioned over the 
hospital ship, hydraulic cylinders 80, 82 are operated to unlock latch 46 
and thereby release carrier 40. The operator then operates the control 
panel switch to lower carrier 40 onto the deck of the hospital ship. As 
carrier 40 is landed onboard the deck of the hospital ship, the acoustic 
rangefinders and contact detectors operate as described above to assure a 
smooth landing. 
The transport system described herein includes a plurality of rangefinders 
and contact detectors to assure accurate readings. The control circuit 60 
thus includes means for comparing the output of the rangefinders and 
contact detectors and disregarding spurious signals which may be generated 
by a defective sensor. The use of a plurality of sensors also provides a 
means to detect the tilt and/or sway of the carrier 40. It should be 
noted, however, that the present invention may be practiced using only one 
rangefinder and/or one contact detector. It should also be noted that the 
rangefinder and contact detector signals may be transmitted to the control 
circuit 60 by means including electromagnetic transmission in addition to 
the hardwire option shown in the preferred embodiment. 
The present invention has been described in terms of a hospital ship litter 
transport system, but it is understood that this is only one application 
of the preferred embodiment and the invention may also be applied to any 
situation where fragile cargo needs to be transferred from one location to 
another especially in situations where there is relative movement between 
the locations. A system consisting of three or more hoists using these 
control systems would be capable of controlling the attitude as well as 
the altitude of the load being transferred. This would allow large loads 
to be transferred between vessels, as the load could be controlled to land 
parallel to the deck of the transfer vessel. 
In summary, an improved cargo transport system includes a control circuit 
and an operator-controlled hoist device. Motion compensation circuitry is 
also included and is operable to vary the movement of the transport 
carrier to compensate for relative motion between the pick-up and delivery 
locations.