GB1248410A - Improvements in or relating to derricks for ships - Google Patents

Abstract

1,248,410. Ships' derricks. TESTING ASSOCIATES Inc. 19 Dec., 1968, No. 60523/68. Heading B8B. A derrick for a ship includes a hollow mast 10 and a fixed housing 11 with sides 11A, 11B carrying a pair of topping lift arms 20, 21 independently rotatable on supports 32 to which they are pivoted on supports 38. A boom 15 is pivoted on supports 14 on a ring 13 supported on rollers on a turntable 12 fixed to the mast 10. The boom 15 is lifted and hauled by a pair of topping lift winches 48A, 48B and a cable 46, see Fig. 9, passing from winch 48A over lead sheave 62A, up the mast 10, over sheaves 61A, 44A and 60A to single block 18A on arm 16A of a yoke 16 pivotally attached to the end of the boom 15. The cable 46 continues over sheaves 54A, 45A, 50A and down the mast 10 to the drum of a winch 65 for two or three turns, then back up the mast 10 and, symmetrically, back to the winch 48B. Operation of winches 48A, 48B clockwise takes up cable and lifts the boom 15. while anticlockwise rotation lowers the boom 15. Rotation of the winch 65, winches 48A, 48B being stationary, swings the boom 15. At 90 degrees from a central starting position, with the boom 15 raised, a null point is reached. In order to continue past the null point for a further 90 degrees swing, arm 20 or 21 must be carried past the null point. To do this the supports 32 are formed as gears. A reversible motor 80 is provided to drive a shaft 81 to engage the gears through centrifugal clutches 82. The motor 80 is brought into action by mechanical switches (not shown) on the arms 20, 21 to carry them over into the adjacent sector, further switches (not shown), cutting the motor 80 after rotating the supports 32 through a selected arc. The boom 15 can thus be swung 180 degrees either way from a central starting position.