671,657. Cranes; loading &c. FARRELL, V. C. Jan. 28, 1948. [June 5, 1945]. No. 2521/48. Class 78 (iv). Hoisting apparatus for use on ships consists of a pair of booms hinged at their heels to points on an athwartship line, and a mast structure disposed between the boom heels, wherein separate topping lifts extend divergingly from separate points at the head of the mast structure to the respective booms, and separate load falls, connected together at their outer ends to form a common load attachment point below and between said booms, are led to separate powered winding drums. In the form described the two booms 10 and 11 are pivotally mounted on horizontal pins in brackets 13, 14 which are in turn pivoted about a vertical axis to further brackets 15, 16 which are bolted to a boom table 12. Table 12 is constructed of two semicircular portions which are bolted together by means of upstanding brackets 41 formed on them, and gear teeth are provided around the circumference or the table by which the latter may be rotated through a pinion 31, the table being supported by rollers 37 running on a track 36 and also by a ball race consisting of a circumferential bracket 44 (cut away) and balls 46 running in a groove on the underside of the bracket and engaging the table's upper surface. The two booms 10, 11 may be united to form a rigid unit, Fig. 1, which may be slewed by rotating the boom table, or may be independently rigged as a Burton rig, Fig. 9, in which case the boom table is locked in the position shown. In the rigid crane structure of Fig. 1, the booms are made rigid with the boom table in a horizontal plane, while allowing movement in a vertical plane by means of diagonal braces 18, 19 secured at their outer ends to the booms and pivoted at their inner ends on horizontal pins in brackets 20, 21 bolted to the boom table. The outer ends of the booms are joined by a further brace 17. A mast 50 is received at its lower end by the boom table and has at its head a fairlead consisting of a rotatable cap 53 on which two swivelling brackets 59, 60, each carrying a roller, are mounted. The cap 53 is mounted for rotation on four sets of ball bearings, not shown, within the mast head. A pair of luffing cables 65, 66, lead from the outer ends of the booms, over the fairlead rollers at the head of the mast, and down within the mast to a clover link 68, from which a single cable supports tackle 69, the cable 70 of which is operated by a winch 72, Fig. 3, situated within the base 35 and driven by a motor 73. Load falls 22, 23 attached to a common hook 126 pass over rollers 24, 25 on the boom heads to separate winch drums 26, 27 driven by motors 28, 29 respectively. When used as a Burton rig, Fig. 9. the boom table is first locked in position. The motor for driving the pinion 31, which is situated within the base and shown at 33, Fig. 3, is for this purpose provided with an electromagnet 34m, Fig. 6, which when energized thrusts a dog 34l into the teeth of a bevel gear 34b which transmits the drive to the shaft 32 of the pinion 31 through a co-operating bevel gear 34a. In addition motor 33 is provided with a clutch 34e, 34f operated by an electromagnet 34k so as to disconnect the motor from the bevel gear 34b and allow it to be used for operating a cable wound on a winch drum 83, Fig. 3, on the opposite end of its main shaft. Thus in the Burton rig of Fig. 9, the diagonal braces 18, 19 and the cross brace 17 have been removed and boom 10 is positioned over the hatch 84 of the ship and boom 11 positioned over the quay 87. Since it is usually not necessary to alter the elevation of the outboard boom 11 during loading the luffing cable 66 is disconnected from the clover link 68 and secured to a fixed point at the foot of the mast. To fix the position of boom 11 a guy rope 85 is extended between the boom head and a point 90 on the deck. Similarly a guy 86 is extended from the head of boom 10 to point 88 on the deck. Points 88 and 90 are chosen to lie on the athwartship line X-X of the ship which also passes through the boom heels. Consequently both booms can be luffed while maintaining their outer ends in the same vertical longitudinal plane, boom 10 being luffed by the winch 72 to position the head of boom 10 over the front or rear of the hatch 84 as desired, while boom 11 is usually in fixed position. Owing to the angle of boom 11 the load fall 23 is removed from winch 27 and instead passed over a pulley 80 on a deck block 81 and through a hole 82 in the base 35 to the winch drum 83 on the main shaft of motor 33. The hook 126 is traversed between the quay and the hatch by simultaneous operation of winches 26 and 83, one paying out while the other winds in. A schooner guy 89 which is used to let out the boom 11 over the quay prior to securing the guy 85, is secured also at a point on the line X-X of the ship. When not in use the braces 17, 18, 19 are again secured in place and the booms lowered until their outer ends are received in recessed blocks 74, 75 to which they are secured by straps 76, 77.