US3661090A

US3661090A - Lateral load transfer

Info

Publication number: US3661090A
Application number: US1579A
Authority: US
Inventors: Gerald Y Martin; John Murray Vines
Original assignee: Minister of National Defence of Canada
Current assignee: Minister of National Defence of Canada
Priority date: 1970-01-09
Filing date: 1970-01-09
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09

Abstract

This application discloses a system for transferring loads laterally between two ships at sea. It makes use of a modification of the known ''''high line'''' wire which carries a traveller supporting the load and is moved to and fro by ''''outhaul'''' and ''''inhaul'''' wires attached to the traveller. In the modification, a single cable is used which acts as the high wire and returns round a pulley as the ''''low wire'''' being anchored at the traveller. The low wire can be divided at the traveller if desired. The ''''loose'''' end of the lower wire is wound on a winch which serves to transfer the load. The geometry of the wires at the traveller tends to keep the load at a constant distance above the water despite relative movements of the two ships.

Description

United States Patent 51 3,661,090 Martin et al. 1 May 9, 1972 [54] LATERAL LOAD TRANSFER 862,748 8/1907 Miller ..214/13 [72] lnventors: Gerald Y. Martin, Bedford; John Murray 11/1965 Shmmger "104/1 H968 Born ..l04/l l4 Vines, Halifax, Nova Scotia, both of Canada Primary Examiner-Arthur L. La Point [73] Assignee: Her Majesty the Queen in right of Canada Assistant F as represented b h Minister f National Attorney-Stevens, Davis, Miller & Mosher Defense of Her Majesty's Canadian Government ABSTRACT 22 i g, 1970 This application discloses a system for transferring loads laterally between two ships at sea. It makes use of a modifica- PP N05 1579 tion of the known high line" wire which carries a traveller supporting the load and is moved to and fro by outhaul" and 521 U.S. c1 ..104/114 2|4 13 254/172 inhaurwiresattached)thetravenermdificatin-a 212/89 212/99 104/] single cable is used which acts as the high wire and returns 511 Int. Cl. ..B6lb 7/02 B6lb 7/04 36% 27/08 a Pulley as wire" being anchoed [58] Field ot-Search 2l4/l3 104/H2 254/172, traveller. The low wire can be divided at the traveller if 512/89 desired. The loose" end of the lower wire is wound on a winch which serves to transfer the load. The geometry of the [56] References Cited wires at the traveller tends to keep the load at a constant distance above the water despite relative movements of the UNITED STATES PATENTS two p 709,916 9/ l 902 Leonard 104/1 14 8 Claims, 5 Drawing Figures PATENTEDHAY 9 I972 3661.090

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L flmm mwm 5 52330 V- ilL l. A m9 $228 7 5223 il 0 a aim J PATENTEDMAY 9 1972 LATERAL LOAD TRANSFER This invention relates to a system for transferring loads laterally and was developed primarily as a system for transferring loads from ship to ship at sea.

The commonly used system for this purpose consists of a high line" wire from which the load is supported by means of a traveller block, the travelling block having connected to it on one side an outhaul wire" and on the other side an inhaul wire". With such an arrangement a man is used to control winches to tension the lines so as to compensate for relative movement between the two ships to which the ends of the high line are connected.

According to the present invention, means for the lateral transfer of bodies from a first station to a second station, comprises at the first station a constant-tension winching system, including a first reversible winch, and a second reversible winch, a first pulley at the first station and a second pulley at the second station, and a first length of cable extending from the first winch over the first pulley to the second pulley and thence to a traveller carriage carried by the part of this length of cable which extends between the first pulley and the second pulley, and a second length of cable extending from the second winch to the traveller carriage, whereby the first winch in use operates to maintain the tension in both lengths of cable substantially constant and the second winch operates to effect movement of the traveller between the first station and the second station.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of two ships between which extends tackle for the lateral transfer of goods;

FIG. 2 is a not-to-scale" representation of the cable arrangement in the tackle of FIG. 1;

FIG. 3 is a diagrammatic representation of a first arrangement of constant-tension winching means indicated diagrammatically only in FIG. 2;

FIG. 4 is a diagrammatic representation of a second arrangement of constant-tension winching means indicated diagrammatically only in FIG. 2; and

FIG. 5 is a diagrammatic representation of a further arrangement of the winching means indicated diagrammatically in FIG. 2.

On a first ship 1 is arranged a first constant tension winching system 3 and a second winching system 5 the speed of operation and the direction of rotation of which is under the manual control of an operator who supervises the load transfer operation. A single cable 7 is wound at one end onto the drum of the winching system 3 and at the other end onto the drum of the winching system 5. The cable extends from the drum of winching system 3 over a fixed pulley 9 carried by ship 1, over a fixed pulley 11 carried by a second ship 13, to a traveller block 15 (at which if desired the cable can be merely clamped to the block or at which alternatively the cable can be broken and have two ends respectively coupled to the traveller block), and back over a fixed pulley 17 on the ship 1 to the drum of the velocity winching system 5.

The constant tension winching system 3 as shown in FIGS. 3 and 4 consists of a winch drum l9 driven by a hydraulic motor 21 fed by a hydraulic pump 23 itself driven by an electric motor 25. The electric motor suitably is a constant speed motor and the winch speed and direction of rotation are varied automatically by adjustment of the pump swash plate or tilthead in such a manner as to tend to keep the tension T in the cable 7 substantially constant. The winching system to this end also includes a rope accumulator 31 consisting of two spaced

pulleys

33 and 35 about which the cable 7 is wrapped, the pulleys being biased apart by a pneumatic cylinder device 37 so that they contain a loop or loops of cable which vary in length to provide an instantaneous reserve of cable to accommodate snatch loads in the cable 7.

FIGS. 3 and 4 illustrate two alternative automatic control systems which can be used to maintain at least an approximation to a substantially constant tension in the cable 7. In the system of F IG. 3, the pulley 9 is carried by an anchor member 41 which includes a steel ring 43 which is distorted by a small but measurable amount by the tension in the cable 7. The distortion of the ring 43 is continuously measured by an electromechanical transducer 45 which acts between diametrically opposite points on the ring, and provides on lead 47 an electrical indication of the strain of the ring and thus of the tension in cable 7. The signal on lead 47 is applied to a comparison device 49 having a control 51 by which a reference electrical signal, indicative of a desired tension in the cable 7, is provided. In part 49A of comparison device 49 the two electrical signals are compared to ascertain whether the tension in cable 7 has departed from the selected desired tension, and any error in the tension provides an output signal in lead 53 which is indicative by its magnitude of the magnitude of the tension error and which is indicative by its sign of the tension error.

The signal on lead 53 is applied to an electro-hydraulic mechanism which adjusts the setting of the swash plate or tilt head of the pump 23. Such mechanisms are well known in the art. This adjustment of the swash plate or tilt head of the pump changes the rate of flow and/or the direction of flow of the hydraulic fluid through the motor 21, so driving. the winch drum 19 to take-in or to pay-out cable to keep the tension in the cable 7 approximately constant.

In order to provide a stable operation of the control system, the pneumatic cylinder device 37 is provided with a stroke/force characteristic which increases the force biasing the

pulleys

33 and 35 apart as they are forced closer together by the tension in the cable 7. For all normal tendencies of the tension in cable 7 to vary from the selected tension, the speed of response of the control system will be sufficient for the tension to remain substantially constant, but on the occurrence of a very sudden increase or decrease in the tension in the part of the cable 7 extending between the two pulleys 9 and 11, the inertia of the parts involved and the finite speed of response of the control system may cause a momentary departure of the actual tension from the desired tension.

In operation of the control system of FIG. 3 with winch 5 stopped, the motor 21 will drive the winch drum l9 alternately in one direction and in the opposite direction to keep the tension in cable 7 substantially constant despite rolling of the two

ships

1 and 13. The action when the second winch 5 is operated will be described below.

In the control system of FIG. 4, a first electromechanical transducer 71 in the form of a direct current tachogenerator is driven from the driving shaft of the winch drum 19, so that the output from this transducer indicates by its polarity the direction of rotation of the drum 19 and indicates by its magnitude the speed of rotation of the drum. A second electromechanical transducer 73 in the form of a direct current tachogenerator is driven by the mounting shaft of the pulley 9, so that the output from this transducer indicates by its polarity the direction of rotation of the pulley 9 and indicates by its magnitude the speed of rotation of the pulley. The arrangement of these transducers is such that the outputs from

transducers

71 and 73 represent to the same scale the velocity of the cable 7 respectively between drum l9 and cable accumulator 31 and between cable accumulator 31 and the pulley 9.

Transducers

71 and 73 are connected respectively by

leads

75 and 77 to the two inputs of a comparison circuit 79, which provides on its output lead 81 an output signal indicative by its magnitude and sense whether cable is being taken-up by, or paid-out from, the cable accumulator 31, and the speed at which this is taking place. The signal on lead 81 is applied as in the arrangement of FIG. 3 to a mechanism which adjusts the setting of the swash plate or tilt head of the pump 23. This adjustment of the swash plate or tilt head changes the rate of flow and/or the direction of flow of the hydraulic fluid through the motor 21, so driving the winch drum 19 to take-in or to pay-out cable in a manner tending to restore the cable accumulator 31 to its initial position. By the use in the pneumatic cylinder device of a stroke/force characteristic which increases the force biasing the

pulleys

33 and 35 apart as they are forced closer together by the tension in the cable 7, this initial position of the cable accumulator 31 will always correspond to the same tension in the cable 7, so that at all times the tension in cable 7 tends to revert to the desired initial tension. As mentioned above in connection with the control system of FIG. 3, the tension cable 7 will, in practice, remain substantially constant apart from rapidly corrected excursions when the tension in the part of the cable 7 extending between the two pulleys 9 and 11 changes very suddenly.

If desired, the control systems of FIGS. 3 and 4 can be used in conjunction, the system of FIG. 3 providing a primary control of the cable tension and the system of FIG. 4 providing a back-up control when a sudden load change occurs.

Referring now to the arrangement shown in FIG. 5, in this arrangement the system of FIG. 3 is used in combination with the arrangement of FIG. 4 to provide more complete control of the tension in the cable 7. The numerals used in FIGS. 3 and 4 are used to denote corresponding parts in FIG. SIA minor deviation is that the comparison device part 49A and the comparison device 79 are replaced with a summing device 91, the two

tachogenerators

71 and 73 being arranged to provide outputs of opposite polarities for corresponding operating conditions, so that when the length of cable in the accumulator 31 is constant these two outputs balance one another, and similarly the polarities of the inputs from the control 51 and the transducer 45 are opposed for corresponding operating conditions, A further deviation is that the output from device 91 is applied to an electrohydraulic valve 93 associated with the output from the hydraulic pump 23 to determine the direction of rotation and the speed of the hydraulic motor 21. In addition, FIG. shows the use of an electric motor 101 to drive a pump 103 which supplies hydraulic fluid under pressure to a hydraulic motor 105 which drives the winch 5 of FIG. 2. A tachogenerator I07 driven by a winch 5 and its output is applied to a summing circuit 109, the second input to which is from a control 111 indicative of a desired transfer speed. By arranging the two inputs to be of opposite polarity for equivalent operating conditions, a simple summing circuit can be used instead of a comparison circuit. The output of the summing circuit 109 is applied to an electrohydraulic valve 113 associated with the output of the hydraulic pump 103 to determine the direction of rotation and the speed of the hydraulic motor 105. The velocity feedback system, described for the velocity winch 5 alternatively can make use of a potentiometer used to monitor the position of a pump tilthead to provide a positive indication of the speed at which the winch 5 is being driven. It will be seen that the winch 5 is automatically driven at a speed and in a direction selected by the setting of the control 111.

Reverting now to consideration of the complete system as shown in FIGS. 1 and 2, at the beginning of the replenishment operation in which stores are conveyed from ship 1 to ship 13, the two ships which will be transferring load are steaming parallel to each other at a speed which will prevent unnecessary rolling between the two ships. A light line is thrown from the supply ship to the receiving ship. Onto this line is attached the block which holds a bight of the wire of the transfer cable. This block is hauled to the receiving ship and then fastened onto the king post, while the controlling officer on the supply ship is paying out cable from the two winches. When this operation is complete, the travelling block is then transferred to the ship which is going to supply the load, The load is then hooked onto the travelling block and the operating ofiicer on the supplying ship tensions the cable and proceeds to transfer the load to the other ship at the same time setting the tension to prevent the load from falling into the sea.

The load L to be transferred between the two ships is coupled to the traveller block 15. The winch 5 is then operated to pay out cable 7, so tending to reduce the tension in cable 7, whereupon the winch 3 comes into operation to maintain the tension at the desired value by taking in cable. As winch S continues to pay out cable at a steady rate, so winch 3 takes in an equal amount of cable also at a steady rate, and the traveller block 15 with the load L moves steadily from ship to ship 13.

Superimposed on this steady taking-in of cable by winch 3 will normally be an oscillatory change in the rate of taking-in cable to compensate for relative movement between the two pulleys 9 and 11 as the ships roll and as minor deviations in the distance between the ships take place.

When the load L has been delivered to the ship 13, the traveller block 15 is caused to return to ship 1 by taking in cable on winch 5, the winch 3 then paying out cable to keep the tension in the cable 7 substantially constant, as before.

The following data relates to the design and operation of a system such as that described above:

Transfer Characteristic Maximum Sea State for Transfer 5 Wave Height HW 8 feet Average distance S between ships I20 feet Normal speed during replenishment 18-20 knots Traveller Speed along cable 7 for Stores I30 ft/min Required Clearance CL between bottom of load and wave crests 20 feet Maximum transfer weight (load L) 1500 lbs. Height of traveller from bottom of load (HL) 8 feet Ship Characteristics Height (HS) of supply ship (1) Derrick above water line feet Height (HR) of receiving ship 13 Derrick above water line 40 feet Mean height (MH) of high line 60 feet Period of roll 10 sec. Angle of roll :IO Assuming metacenter to be on the water line,

Roll are-- :14 ft. Assuming under worst conditions two ships roll apart at same time: Displacement= 28 ft. Maximum displacement of cable 7 due to ships rolling :21 ft. Assuming metacenter to be on water line: Maximum velocity 16 ft/sec Maximum velocity of winch 32 ft/sec Maximum acceleration 22 ft/set:

Inclination between cable and horizontal at ship 13 is 0 radians SYSTEM CHARACTERISTICS It is necessary to determine the tension T required to support the given load under the worst possible conditions: Assuming that the distance between the two ships increased to 300 feet during the transfer operation: I In this situation, the bottom of a load (L) of 1,500 pounds must be held 20 feet (CL) above the crests of the waves (HW). Maximum permissible droop (D) of cable (MH) [(HL) (CL) (HW)] 60 feet [8 feet 20 feet 8 feet] 24 feet Resolving the tension T in the cable into vertical and horizontal components at the point of action of the pulley 11; Vertical component T sin 6 and since the vertical component must equal 1,500 pounds/4 (there being four cable parts acting on the load (L):

T 1,500 pounds/4 sin 9 where sin 6 equals Dl S 24 feet/ I 50 feet i.e. T= 1500/4 X /24 pounds 2,400 pounds TENSION ERROR The tension must not exceed a value which will break the cable or fall below a value which will cause the load to enter the water.

MAXIMUM TENSION Let us assume that the breaking strain of the cable is l2,000 lbs.

MINIMUM TENSION Let the load (L) in FIG. 1 fall to ft above wave crest:

CL 10 ft. D= 34 ft. Sin 6 34/150 0.228 say 0.23 T= 1500/4 Sin 6 0.23

T= 1,600 lbs. Tension change: 800 lbs. 33%

To allow for a safety factor, the tension excursion must not exceed 400 lbs at 2,400 lb level.

System Horse Power Transfer speed-Maximum possible 4 ft/sec Maximum winch speed 8 ft/sec Maximum possible speed of winch 40 ft/sec HORSEPOWER REQUIRED FROM TENSION WINCH HP 550 ft lb/sec HP 40 x 24o 55 =175 HP This applies to the Tensioning winch only.

HORSEPOWER REQUIRED FROM VELOCITY WINCH HP= 4 X 240l55= 17.5 HP The above HP rating applies to winch tension output only.

It is to be noted that all four parts of the cable 7 have a tension T which includes a vertical component tending to support the load L. This enable a cable with a tension of only 2,400 pounds to support a load of 1,500 pounds.

It will be seen that with the load transfer system described above the need for highly skilled winch operating personnel is eliminated while the speed of response of the system is fast enough to ensure that only extreme conditions could lead to wetting of the load L. A further advantage is that the system can be used under conditions of poor visibility, in which although it is relatively easy for the two ships to maintain station by radar, visual observation of the traveller block, to operate a conventional manually-operated-winch high line/low line system, would be impossible.

We claim:

1. Means for the lateral transfer of bodies from a first station to a second station, comprising:

a. at the first station:

i. a first reversible winch;

ii. first drive means for the said first winch;

iii. a second reversible winch;

iv. second drive means, completely independent of the first drive means, for the said second winch;

v. a first pulley;

. at the second station: a second pulley;

c. a first length of cable extending from the first winch over the first pulley to the second pulley;

d. a traveller carriage carried the part of this length of cable which extends between the first pulley and the second pulley;

. a second length of cable extending from the second winch to the traveller carriage;

f. at the first station automatic control means associated with the first reversible winch and adapted automatically to maintain a substantially constant tension in the first length of cable;

g. at the first station, manually operated control means associated with the second reversible winch, and by operation of which the traveller carriage can be moved between the first station and the second station;

h. a cable accumulator effective to absorb snatch loads in the first length of cable comprising:

i. first pulley means;

ii. second pulley means;

iii. a part of the first length of cable between the first winch and the first pulley operatively wrapped around both pulley means;

iv. means biassing the two pulley means apart in a manner tensioning the said part of the first length of cable;

i. a first transducer associated with a first segment of the first length of cable between the first winch and the cable accumulator arranged to provide as output an indication of the velocity of this segment of the cable;

j. a second transducer associated with a second segment of the first length of cable between the cable accumulator and the first pulley arranged to provide as output an indication of the velocity of this segment of the cable;

k. comparison means arranged to compare the outputs of the two transducers, the comparison means being arranged to effect a control of the speed and direction of operation of the first winch such as to tend to restore the equality of the velocities of said first and second segments.

2. Means for the lateral transfer of bodies according to claim 1, and in which:

a. a substantially constant speed electric motor is provided;

b. a hydraulic pump is arranged to be driven by that motor;

0. a hydraulic motor is arranged to be supplied by the hydraulic pump and to drive the first winch; and

d. means to vary the flow of hydraulic fluid between the pump and the hydraulic motor automatically in a manner tending to keep the tension in the two lengths of cable constant.

3. The means of claim 2 including means to automatically measure the tension in the first length of the cable and means connecting said tension sensing means to control said flow varying means.

4. Means for the lateral transfer of bodies according to claim 2, and in which:

a. tension measuring means are arranged to provide a signal indicative of the tension in the first length of cable; and

b. flow controlling means arranged to control the flow of hydraulic fluid between the pump and the hydraulic motor are operated in accordance with the said signal.

5. Means for the lateral transfer of bodies according to claim 4, and in which:

a. supporting means are provided for the first pulley; and

b. the tension measuring means includes an electromechanical transducer arranged to measure distortion of the sup porting means and thus the tension in the first cable length.

6. The means of claim 1 including:

a. means to automatically measure the tension in the first length of cable;

b. means to apply said tension measuring means to control the direction and speed of rotation of the first winch so as to keep the cable tension constant.

7. Means for the lateral transfer of bodies according to claim 1, and including:

a. a first set of pulleys;

b. a second set of pulleys;

c. a part of the first length of cable between the first winch and the first pulley operatively wrapped round both sets of pulleys;

d. means biassing the two sets of pulleys apart in a manner tensioning the said part of the first length cable;

the sets of pulleys and the biassing means forming together a cable accumulator effective to absorb snatch loads in the first length of cable.

8. Means for the lateral transfer of bodies according to claim 7, and in which:

a. a first transducer associated with the part of the first length of cable between the first winch and the cable accumulator is arranged to provide as output an electrical indication of the velocity of this part of the cable;

b. a second transducer associated with the part of the first length of cable between the cable accumulator and the first pulley is arranged to provide as output an electrical indication of the velocity of this part of the cable;

c. comparison means are arranged to compare the outputs of the two transducers; and

d. the comparison means are arranged to effect a control of the speed and direction of operation of the first winch such as to tend to restore the equality of the velocities of these two parts of the cable.

Claims

1. Means for the lateral transfer of bodies from a first station to a second station, comPrising: a. at the first station: i. a first reversible winch; ii. first drive means for the said first winch; iii. a second reversible winch; iv. second drive means, completely independent of the first drive means, for the said second winch; v. a first pulley; b. at the second station: a second pulley; c. a first length of cable extending from the first winch over the first pulley to the second pulley; d. a traveller carriage carried the part of this length of cable which extends between the first pulley and the second pulley; e. a second length of cable extending from the second winch to the traveller carriage; f. at the first station automatic control means associated with the first reversible winch and adapted automatically to maintain a substantially constant tension in the first length of cable; g. at the first station, manually operated control means associated with the second reversible winch, and by operation of which the traveller carriage can be moved between the first station and the second station; h. a cable accumulator effective to absorb snatch loads in the first length of cable comprising: i. first pulley means; ii. second pulley means; iii. a part of the first length of cable between the first winch and the first pulley operatively wrapped around both pulley means; iv. means biassing the two pulley means apart in a manner tensioning the said part of the first length of cable; i. a first transducer associated with a first segment of the first length of cable between the first winch and the cable accumulator arranged to provide as output an indication of the velocity of this segment of the cable; j. a second transducer associated with a second segment of the first length of cable between the cable accumulator and the first pulley arranged to provide as output an indication of the velocity of this segment of the cable; k. comparison means arranged to compare the outputs of the two transducers, the comparison means being arranged to effect a control of the speed and direction of operation of the first winch such as to tend to restore the equality of the velocities of said first and second segments.

2. Means for the lateral transfer of bodies according to claim 1, and in which: a. a substantially constant speed electric motor is provided; b. a hydraulic pump is arranged to be driven by that motor; c. a hydraulic motor is arranged to be supplied by the hydraulic pump and to drive the first winch; and d. means to vary the flow of hydraulic fluid between the pump and the hydraulic motor automatically in a manner tending to keep the tension in the two lengths of cable constant.

4. Means for the lateral transfer of bodies according to claim 2, and in which: a. tension measuring means are arranged to provide a signal indicative of the tension in the first length of cable; and b. flow controlling means arranged to control the flow of hydraulic fluid between the pump and the hydraulic motor are operated in accordance with the said signal.

5. Means for the lateral transfer of bodies according to claim 4, and in which: a. supporting means are provided for the first pulley; and b. the tension measuring means includes an electromechanical transducer arranged to measure distortion of the supporting means and thus the tension in the first cable length.

6. The means of claim 1 including: a. means to automatically measure the tension in the first length of cable; b. means to apply said tension measuring means to control the direction and speed of rotation of the first winch so as to keep the cable tension constant.

7. Means for the lateral transfer of bodies according to claim 1, and including: a. a first set of pulleYs; b. a second set of pulleys; c. a part of the first length of cable between the first winch and the first pulley operatively wrapped round both sets of pulleys; d. means biassing the two sets of pulleys apart in a manner tensioning the said part of the first length cable; the sets of pulleys and the biassing means forming together a cable accumulator effective to absorb snatch loads in the first length of cable.

8. Means for the lateral transfer of bodies according to claim 7, and in which: a. a first transducer associated with the part of the first length of cable between the first winch and the cable accumulator is arranged to provide as output an electrical indication of the velocity of this part of the cable; b. a second transducer associated with the part of the first length of cable between the cable accumulator and the first pulley is arranged to provide as output an electrical indication of the velocity of this part of the cable; c. comparison means are arranged to compare the outputs of the two transducers; and d. the comparison means are arranged to effect a control of the speed and direction of operation of the first winch such as to tend to restore the equality of the velocities of these two parts of the cable.