Patent GB-1143102-A (GB)
Title: Method and apparatus for replenishment at sea
IPC: B63B27/18
Filed: 1966-02-11
Abstract: 1,143,102. Winches; trans-shipping at sea. ABEX CORP. 11 Feb., 1966 [11 Feb., 1965], No. 6261/66. Headings B8B and B8E. [Also in Division G3] In an apparatus for transferring an article conveying trolley 13 between a pair of relatively moving ships 11, 12, the tension in a trolley transfer cable 30 is maintained at a preset value by automatically controlling the speed and direction of inhaul and outhaul hydraulic winches 31, 33. The latter are controlled in response to signals from a cable tension sensing device 34, 35 adjacent each winch 31, 33 which devices act as energy storage units to absorb sudden changes in tension in the cables, which due to the time lag in operation of the winch drive system cannot be compensated for immediately by the winches. In the embodiment of Fig. 1 a highline 14 is used, along which the trolley 13 runs, the line 14 which has one end anchored on the ship 12 is tensioned by an hydraulic winch 23 on the ship 11, the line being wrapped around two sets of pulleys 24, 25 biased apart by an hydraulic accumulator ram 22 adjacent, the winch 23. The latter may be controlled either manually, or automatically in response to an amplified potentiometer signal, the feedback voltage of which is a measure of the relative displacements of the two sets of pulleys 24, 25, and controls the swash plate setting in the hydraulic pump driving the motor of the winch 23. Each transfer cable tension sensing device 34, 35 comprises a spring-loaded ram, Fig. 12 (not shown), the cable passing over a spring biased pulley on the ram piston, between passing around a pair of pulleys on the exterior of the cylinder, and a vibration damping fluid dashpot is associated with the piston. A wiper on the piston of each device 34, 35 moves along a potentiometer coil on the cylinder thereof to produce a feedback voltage which is a measure of the piston movement, and hence the cable tension. The potentiometer arrangement may be replaced by a linear variable differential transformer. Several modes of operation of the apparatus are possible the electrical control circuit of which is shown in Figs. 5, 6, 7, 8 (not shown). A manual speed control mode is selected to wind in or pay out cable without any preselected tension, each winch having its own control. In a manual tension control mode, a preset minimum cable tension in the form of a command voltage signal is set in the control circuit for each winch and is compared with a signal representing a tension manually set for each winch, by which comparison the winch hydraulic pump outputs are controlled to cause the trolley to move in a desired direction while the preset minimum tension is maintained. In an automatic control mode a preset cable tension in the form of a command voltage signal is set in the circuit for each winch and is compared with the associated sensing device feedback signals, by which means the winch pump outputs are controlled to maintain a constant tension in the transfer cable as the ships move relative to each other. In addition to maintaining a constant tension, the trolley is automatically controlled for leaving one ship with the fastest permissible velocity, and upon approaching the other ship the control may be switched so that either the trolley moves at a preset slow velocity relative to the receiving ship, or that the trolley remains at a fixed distance from the receiving ship. In the embodiment of Fig. 3 (not shown), the trolley rolls along the upper run of the transfer cable and the highline cable is not required.