US3606256A

US3606256A - Winch control systems

Info

Publication number: US3606256A
Application number: US738927A
Authority: US
Inventors: Karsten Alfred Overetveit
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-06-21
Filing date: 1968-06-21
Publication date: 1971-09-20
Anticipated expiration: 1988-09-20

Abstract

IN A CABLE CONVEYOR SYSTEM FOR TRANSFER OF CARGO BETWEEN MOVING OBJECTS SUCH AS TWO SHIPS WHERE A LOOP OF WIRE IS SLUNG OVER A PULLEY ON ONE SHIP AND THE TWO ENDS OF SAID WIRE ARE SLUNG OVER INDENPENDENT PULLEYS ON THE OTHER SHIP, WHERE THE TWO WIRE ENDS ARE INDEPENDENTLY OPERATED BY TWO HYDRAULIC WINCHES HAVING A COMBINED WINCH CONTROL SYSTEM WHEREBY ONE WINCH IS USED AS A TENSIONING WINCH AND THE OTHER IS USED AS A SPEED AND DIRECTION CONTROL WINCH, AND INCORPORATING FEEDBACK SYSTEMS WHEREBY THE ACCELERATION, SPEED, DECELERATION AND STOP POSITION OF SAID CONTAINER CAN BE PREDETERMINED RELATIVE TO ONE SHIP OR THE OTHER IRRESPECTIVE OF THE ROLLING OF SAID TWO SHIPS.

Description

P 20, 1971 K. A. OVRETVEIT 3,606,256

WINCH CONTROL SYSTEMS Filed June 21, 1968 2 Sheets-Sheet l p 20, 1971 K. A. OVRETVEIT WINCH CONTROL SYSTEMS Filed Jun 21, 1968 2 Sheets-Sheet z Fig. 3.

United States Patent Oifice 3,606,256 Patented Sept. 20, 1971 3,606,256 WINCH CONTROL SYSTEMS Karsten Alfred Ovretveit, 87 Lower Road, Fetcham, Surrey, England Continuation-impart of application Ser. No. 608,636,

Jan. 11, 1967. This application June 21, 1968, Ser.

Int. Cl. B66d 1/48 US. Cl. 254-172 6 Claims ABSTRACT OF THE DISCLOSURE In a cable conveyor system for transfer of cargo between moving objects such as two ships where a loop of wire is slung over a pulley on one ship and the two ends of said wire are slung over independent pulleys on the other ship, Where the two wire ends are independently operated by two hydraulic winches having a combined winch control system whereby one winch is used as a tensioning winch and the other is used as a speed and direction control winch, and incorporating feedback systems whereby the acceleration, speed, deceleration and stop position of said container can be predetermined relative to one ship or the other irrespective of the rolling of said two ships.

This is a continuation-in-part of application Ser. No. 608,636 filed J an. 11, 1967, now abandoned, entitled Winch Control Systems.

This invention relates to improvements in winch control systems, for example for the control of cable conveyors for the transport of goods from one ship to another.

An object of the invention is to provide a winch control system in which the continual variation in tension in the winch cable is reduced. It is desirable to maintain a predetermined tension in outhaul and inhaul wires whilst the two ships or other supports for the ends of the cables move apart and move towards each other. It is desirable to maintain a predetermined speed of transport of the goods relative to the two ships during rolling and tossing movements of the two ships towards and away from each other. It is also desirable to stop the goods at a predetermined position on the cables extending between the two ships relative to the two ships, irrespective of the relative movements of the ships together and apart. It is also desirable to lift and lower the goods vertically while the goods are held at a predetermined point relative to the two ships.

The invention consists in a winch control system including a first winch motor for rotating a first winch barrel, a second winch motor for rotating a second winch barrel, a pressure fluid source for supplying pressure fluid to the first and second winch motors, first winch motor control means for controlling the flow of pressure fluid from the pressure fluid source to the first winch motor in response to fluid pressure from an auxiliary pressure fluid source, compensating control means connected to the secnd winch motor, auxiliary control means adapted to control the flow of pressure fluid from the auxiliary pressure fluid source to the first winch motor control means and fluid connecting means for connecting the first winch motor control means with second winch motor compensating means.

Preferably the first pressure reponsive means adapted to sense the fluid pressure supplied to the first winch motor and adapted to control the auxiliary control means in response thereto and second pressure responsive means adapted to sense the fluid pressure supplied to the second winch motor and adapted to control the auxiliary control means in response thereto so that the speeds of the first and second winch motors are varied to accommodate a change in tension exerted on the first and second winches respectively.

Preferably the first winch motor control means includes a synchronizing valve having a first rotary member adapted to be connected to the first winch motor and a second rotary member adapted to be connected to a first control motor adapted to receive pressure fluid from the auxiliary pressure source to control the rotary speed of the first Winch motor, the compensating control means including a compensating control pump of substantially equal volumetric capacity to the first control motor.

In order that the invention may be clearly understood and readily carried into effect, reference is directed to the accompanying drawings.

FIG.1 shows a diagrammatic example of la winch system for transfer of cargo from one ship to another without showing a high line.

FIG. 2 shows a diagrammatic arrangement where two winches are working together, one winch is working as a tensioning winch and the other is working as a speed control winch.

FIG. 3 is a schematic flow diagram of part of the in- Vention and includes a diagrammatic cross section of a double rotary synchronising valve and a multistage fourway slide valve.

In FIG. 1, on the deck 1 of the replenishing ship A there is fitted a tensioning winch T and a speed control winch SC. On the replenishing ship A there is fitted a pulley support 9 which can be moved up and down by power 99 from a hydraulic motor 10 and two pulleys 3 and 7 are fastened to the pulley support 9 at a suitable distance from each other.

On the receiving ship B, there is fitted a pulley support 11 carrying a pulley '4 and capable of being moved up and down by a motor 12.

From the winch barrel 20 on the tensioning winch T a wire 2 leads over the pulleys 3, 4 and is fastened to wires 5 at a container 6. The wire 5 leads over a pulley 7 to the winch barrel 19 on the speed control winch SC.

The container 6 is hung by the pulley 8 on the wire 2 and the container 6 is fastened to the

wires

5 and 2.

In FIG. 2, the winch barrel 19 on the speed control winch SC is driven by a closed circuit hydraulic transmission consisting of a supply pump 14, a hydraulic winch motor 17 arranged to drive said 'winch barrel 19 and oil supply and

return pipes

26 and 27 connecting the supply pump 14 to the hydraulic winch motor 17.

Control valves

21, 25 and 33 are arranged to control the rotating direction and speed of said hydraulic winch motor 17.

The barrel 20 on the tensioning winch T is driven in a similar manner by a closed circuit hydraulic transmission consisting of a supply pump 15, a hydraulic winch motor 18, arranged to drive the said winch barrel 20, and oil supply and

return pipes

29 and 30 connecting the supply pump 15 to the hydraulic winch motor 18.

Control valves

22 and 28 are arranged to control the rotating direction and speed of the hydraulic winch motor 18.

The arrangement for expansion and contraction of the closed oil circuits to accommodate temperature variations is not shown.

The winch barrel 19 is fitted on hearings on the shaft of the speed control winch SC and the winch barrel 19 is connected to the winch barrel shaft by a friction clutch which is set for a torque above the requirement for the maximum tension of the

wires

2 and 5 but safely below the maximum tension which the

wires

2 and 5 and the associated rigging can sustain.

The winch barrel 20 is fitted in a similar way on the shaft of the tensioning winch T. The winches SC and T are fitted with guide devices for guiding the wire onto the winch barrels automatically.

The

control valves

25 and 28 are arranged to pass slightly more oil to the

hydraulic winch motors

17 and 18 respectively than the quantity required for any specific rotation speed in order to enable the

hydraulic winch motors

17 and 18 to react instantaneously to maintain constant tension in the

wires

2 and 5 during violent move ments by the ships A and B. The surplus oil from the

supply pumps

14 and 15 which is not absorbed. by the

hydraulic winch motors

17 and 18 respectively, is relieved through safety valves 59 and 60 back to the

supply pumps

14 and 15 respectively.

The winches SC and T are also protected from overloading by

safety valves

31 and 32 respectively, which are set to leak oil at a slightly higher oil pressure than the pressure required for the transport of cargo but well below the maximum oil pressure which the

wires

2 and 5 and the associated rigging can sustain.

The rotation speed of the winch SC is governed by a double rotary control valve 33 with one valve rotor rotating inside the other, for example as described in my co-pending application No. 555,023. This rotary control valve 33 is fitted between the

pipes

26, 27 and the control valve 21 for the hydraulic winch motor 17 on the winch SC. The oil flow to and from the hydraulic winch motor 17 is controlled by the rotary control valve 33. The shaft of the hydraulic winch motor 17 is connected through gearing 34 to one of the rotors in the rotary control valve 33 so that the rotation of the shaft of the hydraulic winch motor 17, and thereby the barrel 19, will follow accurately the rotation of a second rotor, arranged in the rotary control valve 33, for rotation in both rotating directions and for stop.

The second rotor in the rotary control valve 33 can be rotated by a controllable rotary hydraulic motor 35 with fixed volumetric capacity. The hydraulic motor 35 is driven by a pump 36 with supply and return pipes 39, 40 through

control valves

38, 41. The pump 36 is driven by an electric motor 37.

The control valve 38 controls the rotating speed of the hydraulic motor 35 and the rotary control valve 33 and thereby the speed of the hydraulic winch motor 17, and the winch barrel 19, from stop to maximum speed in both rotating directions.

The

pipes

29, 30 are connected by pipes 43 and 42 respectively to a pilot valve 51 on the control valve 41. Similarly, the pipes 61 and 62 connect the

pipes

26 and 27 respectively to the pilot valve 63 on the control valve 41. If the tension in the

wires

2 or 5 should cause the oil pressure in the

pipes

30 or 29 or alternatively in the

pipes

26 or 27 to rise above a predetermined level, then the rise in oil pressure will cause the pilot valve 51 or alternatively, the pilot valve 63, to operate the valve slide in the control valve 41, thereby regulating the volume of oil from the pump 36 through the control valve 38 to the hydraulic motor 35 to decrease or increase the rotation speed of the hydraulic Winch motor 17 automatically and thereby cushion against the inertia which otherwise would have been created by the weight in the container 6 if the container 6 suddenly changed speed violently due to the rolling of the ships A and B during the transfer of said container 6 from one ship to the other.

By this cushioning method, a greater transfer speed can be achieved or a greater load can be transferred without increase in the strain or the transfer installation.

When the container 6 approaches close to ship A or B the transfer speed of the container 6 is automatically slowed down and the need for the above cushioning effeet is reduced, and may become undesirable. The container 6 is set by the

contactors

46 or 49 at the operational stage so as to move at a predetermined speed relative to that ship which the container 6 is approaching.

A gear 72 connects the shaft of the hydraulic winch motor 18 to drive a pump 52. This pump 52 is of the fixed volumetric capacity type and of exactly the same volumetric capacity as the hydraulic motor 35. Pipes 54 4 and 55 connect the pump 52 to the hydraulic motor 35 and also to the pump 36 through the pipes 39 and 40.

When the pump 52 is driven by the hydraulic winch motor 18 through gear 72, and the volume of oil from the pump 36 is cut off, the volume of oil from the pump 52 is arranged to drive the hydraulic motor 35 in the same rotating direction and exactly the same rotating speed as the pump 52. Thereby, the two winches SC and T are synchronized and arranged to heave in or pay out wire at exactly the same speed and in the same direction.

When the winches SC and T are set to rotate in opposite directions to each other when the winches are to be used for the transfer of cargo between the ships A and B, the hydraulic motor 35 and the pump 52 will ab sorb exactly equal amounts of the oil delivered by the pump 36 providing that the winch barrels 19 and 20 are rotating at equal speeds but in opposite directions. Any change of speed of the winch T while the pump 36 delivers oil, will cause an equal but opposite change of speed on the Winch SC.

When the control lever 48 is moved to the vertical stop position the control valve 38 cuts off the flow of oil from the pump 36 to the hydraulic motor 35 and the pump 52. The transfer of the container 6 is then stopped. And, in addition to the function of the pump 52 causing the winch SC to be synchronized with the winch T, the hydraulic motor 35 can be connected to the pump 52 automatically by clutch 47 when the control lever 48 is moved to the vertical stop position.

The winch barrel 19 is geared and 77 to mesh with a geared portion 71 of a screw 45 to rotate the screw 45 which is in screw-threaded engagement with a threaded 46b contactor 46 fitted in sleeve 46a] to slide along a slot 73 therein, sleeve 4641 being similarly geared to the winch barrel 20*. Said sleeve 46a has a geared portion 44 in mesh with a gear 53 on the winch barrel 20', but at the same time the contactor 46 is arranged to follow the axial drive of the screw 45. The position of the contactor 46, is therefore always an indication of the distance between the container 6 and the pulley 4 on the ship B.

When the container 6 approaches ship B, the contactor 46 is arranged 490 to gradually move the valve slide in the control valve 38 to cause gradual reduction of transfer speed of the container 6 towards ship B until the contactor 46 has caused the control valve 38 to stop the winches SC and T, and thereby stop the movement of the container 6 relative to ship B. The container 6 will then be held in suspension over the deck of the ship B at a predetermined distance from the pulley 4.

The container 6 can also be arranged to be pulled up against a support on ship B at an absolute controlled rate of speed relative to ship B, irrespective of the rolling of the ships A and B, due to the compensating function of the pump 52.

The winch barrel 19 is also geared 77 to rotate a screw 50 into a threaded contactor 49. Said contactor 49 does not rotate, but is arranged to follow the axial drive of said screw 50.

When the container 6 approaches the ship A to a safe distance x from said ship A, the contactor 49 is arranged by lever 490 to regulate a control valve 57, to cut off the oil communication between the pump 52 and the hydraulic motor 35. The oil in said pump 52 is then merely circulating in said pump 52. When the valve 57 is closed to stop oil from flowing to and from pump 52, the position of the contactor 49 is always relative to the distance between the container 6 and the pulley 7 on the ship A. The contactor 49 also, at the same stage, causes the volume of oil delivered by the pump 36, to be cut to half volume to maintain the correct and predetermined speed of the container 6 relative to ship A. The winch T will then heave in and render wire to compensate fully for the rolling of the ships A and B.

As the container 6 moves closer to said ship A, the contactor 49 regulates by lever 490 the control valve 38 to gradually reduce the speed of the container 6, until the contactor 49 has moved the valve slide in the control valve 38 to the position for cutting otf the flow of oil from the pump 36 to the hydraulic motor 35. Said hydraulic motor 35 will then stop and cause the winch SC to stop. The container 6 will then be held in suspension over the deck of ship A at a predetermined distance from the pulley 7. The winch T is, at this stage, merely maintaining the predetermined tension in the

wires

2 and 5 by heaving in and surrendering wire as the ships A and B are moving together and away from each other.

When the control lever 48 is moved to the vertical stop position, the control valve 38, cuts off the flow from the pump 36 to the hydraulic motor 35. This stops the container 6 at any predetermined distance from its stop position over the deck of ship A or at a predetermined safe distance x from the side of ship A.

When the contactor 49 cuts off the flow of oil from the pump 36 to the hydraulic motor 35 for stopping the container 6 automatically at the predetermined position over the deck of ship A, the control lever 48 is automatically moved to the vertical stop position. When the lever 48, then, is moved approximately 5 to the left to the position for lowering, or 5 to the right for lifting, the hydraulic motor 10, which lifts and lowers the pulley support 9', is automatically series coupled through the control valve 38 with the hydraulic motor 35. The volumetric capacity of said hydraulic :motor 10 is so arranged relative to the hydraulic motor 35, that the lifting and lowering of the pulley support 9 is at the same speed and synchronized with the heaving in and rendering respectively, by the winch SC. The container 6 can therefore be lowered or lifted but remain at the same distance from the pulley 7. When the pulley support 9, on its down ward movement has reached a predetermined position, the oil diow from the pump 36 will be cut off automati cally and the pulley support and the winch SC will stop and the container 6 will remain at a constant distance from the pulley 7. When the pulley support 9 reaches a predetermined height, then the valve 38 cuts off the oil connection to the hydraulic motor 10 automatically and the upwards movement of the pulley support 9 and the container 6 will stop, but if the control lever 48 is not moved back to the vertical stop position, then the paying out of wire by the winch SC will continue and the container 6 starts to move towards ship B automatically. The further the lever 48 is moved to the right, the faster the container 6 will move towards ship B.

During the lifting of the container 6, the winch T functions merely as a tensioning winch by heaving in and rendering wire as the ships A and B move together or away from each other, respectively.

When the container 6 has moved to a safe and predetermined distance x from the side of ship A, the contactor 49 connects the flow of oil from the pump 52. to the hydraulic motor 35, thereby causing the container 6 to move at a predetermined constant speed, relative to the ship B, even if the ships A and B move together and away from each other. This effect is achieved by the functions of the pump 52 in the following manner:

When the flow of oil from the pump 36 to the hydraulic motor 35 and to the pump 52 is cut off and the ships A and B are steady, relative to each other, then the winches SC and T are stopped and the container 6 is held in suspension at a fixed distance between said ships A and B for example, as shown in FIG. 1.

If the ships A and B then roll away from each other, the winch T will reverse to pay out wire and the reversing of said winch T will drive the pump 52 in reverse and this will cause the hydraulic motor 35 to reverse and thereby synchronize the reverse rotation of winch SC with said winch T, and winch SC will consequently pay out wire at exactly the same speed as winch T. The container 6 will then be held at a predetermined distance, relative to the pulley 4 on the ship B.

When the ships A and B roll towards each other, the pump 52 will then be driven by winch T in the opposite direction and drive the hydraulic motor 35 in the same direction, thereby synchronizing the rotating direction and rotating speed of the Winch SC, with the winch T. The two winches SC and T will consequently heave in wire at exactly the same speed and this will hold the container 6 at a constant distance from the pulley 4 on ship B.

When the winches are set tomove the container towards ship B, and said ships A and B maintain the same distance between each other, the volume of oil from the pump 36 is divided equally between the hydraulic motor 35 and the pump 52, since said hydraulic motor 35 and said pump 52 are both of equal and fixed volumetric capacity. The flow of oil from the pump 36 will not drive the pump 52, but the hydraulic motor 35 starts to rotate in the rotating direction set by the control valve 38, in this case for paying out wire from the winch SC. This will cause said winch T to heave in wire at the same speed as said winch SC is paying out wire to retain the preset tension in the wires 2. and 5. As the winch barrel 20 rotates at the same speed as winch barrel 19, the pump 52 will rotate at exactly the same rotation speed as said hydraulic motor 35, because the pump 52 will, under this condition, absorb exactly half the volume of oil supplied by the pump 36. The container 6 will, therefore, move towards ship B at a constant speed relative to ship B.

If the ships A and B move away from each other whilst the container 6 is moving towards ship B, then the winch T will slow down so that the said winch T should not increase the preset tension in the

wires

2 and 5. Consequently, the pump 52 slows down and leaves more of the oil from pump 36 to be directed to the hydraulic motor 35 with the result that the winch SC will increase its speed for paying out wire in exactly the same proportion as the winch T has reduced its speed for heaving in wire. This will cause the container 6 to move towards the ship B at a constant speed relative to ship B.

Whilst the control valve 38 is set for moving the container from one ship to the other and the pump 52 is engaged, then it follows that any change in rotation speed of winch T and pump 52 will automatically cause an exact opposite relative change of rotating speed on the hydraulic motor 35 and winch SC until the said ships A and B are moving at a greater speed together or away from each other, then the container 6 is set for moving from one of said ships to the other. Then both winches will operate in the same direction, but one winch will operate faster than the other because the movements of the ships are greater than the speed at which the container is moving relative to the pulley 4 on ship B. The transfer speed of the container 6 will therefore, be constant relative to the pulley 4 on the ship B.

If the ships A and V are moving away from each other at a greater speed than the predetermined transfer speed for the container 6 for moving towards ship B, then the winch T has to reverse and pay out wire and the pump 52 will not absorb oil from the pump 36, but said pump 52 will deliver a volume of oil in reverse, which will be added to the total volume of oil from the pump 36 to the hydraulic motor 35. The reversal of oil flow from the pump 52 will be the exact volume required to drive the hydraulic motor 35 at the required speed to regulate the winch SC to compensate for the increase in speed of paying out wire above the speed at which the control valve 38 is set for moving the said container 6 towards said ship B. The container 6 will, therefore, move towards ship B at a constant speed relative to the pulley 4 on ship B, and this speed is not influenced by the rolling of the ships A and B. As long as the pump 52 is connected to the hydraulic motor 35 and the pump 36, the transfer speed of the container 6 is always constant relative to pulley 4 on ship B under all conditions of rolling of the ships A and B.

When the container 6 approaches the ship B, the contactor 46 causes the speed of said container 6 to gradually slow down to stop at a predetermined position adjacent to the pulley 4, either tight up against a cushioning support above the deck of the ship B or held in suspension over the deck of said ship B at a fixed distance from the pulley 4 as required.

The contactor 46 can be arranged to automatically clutch 47 said pump 52 and said hydraulic motor 35 together when the movement of said container 6 is stopped relative to said ship B to further ensure that the winches SC and T will render and heave in wire simultaneously and thereby hold the container 6 at an exact predetermined position relative to the pulley 4.

The container 6 can then be lowered vertically towards the deck of ship B by lowering the pulley support :11.

The container 6 can again be lifted in a similar manner by lifting the pulley support 11.

During the return of container 6 to the ship A, the

function of the winches SC and T are similar to the function of said Winches SC and T for moving said container 6 to the ship B, the winches SC and T are merely Working in the opposite direction.

But when the container 6 approaches to within a safe distance x of the ship A, the contactor 49 is arranged to cut off the pump 52 from oil communication with the hydraulic motor 35 and pump 36 so that the container 6 will move at a constant speed relative to pulley 7 on ship A and gradually slow down the movement of the container 6 relative to the pulley 7 until said container 6 stops automatically at a predetermined position relative to the pulley 7, either tight up against a cushioning support above the deck of said ship A or the container 6 is held in suspension over the deck of said ship A at a fixed distance from pulley 7.

The container 6 can then be lowered as described above.

If it is desired to lower the container 6 at any position between the pulleys 3 and 4 without lowering the pulley support 9 or 11, the container is stopped relative either to ship A or ship B by moving the transfer control lever 48 to the vertical stop position. The container 6 can then be lowered by moving the control levers 23 and 24 forward which will override the tensioning control for the winches SC and T and reduce gradually the torque of the winches SC and T, thus lowering the container 6 to the desired level.

This method can, for example, be used for lowering the container 6 down to a small vessel between the ships A and B.

When the levers 23 and 24 are again set back to automatic tensioning position, the container 6 will then be lifted again ready for transfer to ship A or ship B.

The difference to tension in the wires 2 and when the winches SC and T are heaving in and slowing down to stop and reversing, due to the loss of efiiciency of winches SC and/or winch T, the rotation direction and speed of winches SC and T is arranged to regulate the safety valves 59, 60 and/or the

control valves

25, 28, respectively, relative to the efiiciency variations of said Winches SC and/or T.

Similarly, compensation for efficiency variations for other components in a transfer of cargo at sea arrangement such as pulleys, wires and ram tensioners, can be arranged to regulate said safety valves 59, 60 and said

control valves

25, 28, to maintain constant tension on the wires 2 and/or 5.

What I claim is:

1. A winch control system for moving a container between two relative moving objects including, a first cable winch carrying a first cable, a first winch motor driving said first winch, a second cable winch carrying a second cable, a second winch motor driving said second winch,

said first and second cables being connected to said container, a pressure fluid source for supplying pressure fluid to the first and second winch motors, an auxiliary pressure fluid source wherein the improvement comprises in combination a first motor control valve with control means controlling the flow of fluid from the pressure source to the first winch motor in response to fluid pressure from said auxiliary pressure fluid source and in response to the rotation of the first motor, compensating control means driven by the second winch motor, auxiliary control means controlling the flow of fluid from the auxiliary source to the first motor control means, fluid connecting means connecting the first motor control means with said second motor compensating control means, a first pressure responsive means for predetermined control of the said first and second winch motor, a secondary auxiliary control means sensing the fluid pressure supplied to said first winch motor and selectively controlling the secondary auxiliary control means in response thereto, and second pressure responsive means sensing the fluid pressure supplied to said second winch motor and selectively controlling said secondary auxiliary control means in responsive thereto so that the speed of the first and second Winch motors are varied to accommodate an excessive change in cable tension exerted on the first and second cable winches.

2. A winch control system as claimed in claim I wherein the first winch motor control means includes a synchronising valve having a first rotary member adapted to be connected to the first winch motor and a second rotary member adapted to be connected to a first control motor adapted to receive pressure fluid from the auxiliary pressure source to control the rotary speed of the first winch motor, the compensating control means including a cornpensating control pump of substantially equal volumetric capacity to the first control motor.

3. A winch control system as claimed in claim 1 including indicating means comprising a first screw member adapted to be rotated by one winch motor and having a screw-threaded portion in screw-threaded engagement with a receiving member adapted to be rotated by the other winch motor and axially movable so that rotation of the first motor relative to the second motor moves the receiving member axially.

4. A Winch control system as claimed in claim 3 including indicator connecting means to connect the receiving member with the auxiliary motor speed control means so that the operation of the first and second winch motors is controlled by the position of the receiving member.

5. A winch control system as claimed in claim 2 including clutch means adapted to connect the first control motor with the compensating control pump when it is required that the tWo Winch motors should operate in unison.

6. A winch control system as claimed in claim 1 including an additional motor adapted to raise and lower one of the pulleys to raise or lower the container when adjacent the pulley, the additional motor being adapted to be connected to the auxiliary control means.

References Cited UNITED STATES PATENTS 3,206,875 9/1965 Cargile 254-172 3,231,241 1/1966 Lottermoser 254-172 3,279,761 10/1966 Schreiber 254-172 FOREIGN PATENTS 1,007,428 10/ 1965 Great Britain 254-184 HARVEY C. HORNSBY, Primary Examiner US. Cl. X.R.