GB560796A - Improvements in or relating to grabs - Google Patents

Abstract

560,796. Grabs; raising sunken objects. WATSON, A. J. G. Oct. 16, 1942, No. 14525. [Classes 78 (iv) and 78 (v)] [Also in Group XXI] Relates to a grab of the type comprising jaws 31, Fig. 2, operatively connected with a piston 24 and arranged to engage the object to be raised when the piston is moved upwards in its cylinder 22 by pneumatic means creating a difference in air pressure on opposite sides of the piston. According to the invention, the cylinder has a jacket to contain air for increasing the buoyancy of the grab when it is used for salvaging submerged objects. The arrangement shown, for raising a sunken submarine 33, Fig. 1, comprises an armourplated, cigar-shaped drum 10 supported by cables 11, 11a from two ships 12, 12a, a third ship 17 supporting a diving-bell 18 in telephone communication with the three ships and carrying a searchlight to illuminate the sea-bed. Each cable 11, 11a is led into a hawse-hole 13, Fig. 4, in the ship through rings 15 on a leafspring 14 which is supported by a bracket 16 and a projecting part 13a of the hawse-hole frame. The drum 10 is formed with inner and outer cylindrical shells 34, 35, between which the pivots 30 of the jaws 31 are arranged, and carries two identical grab devices 21, Fig. 1. For operating each grab, arms 29 integral with the jaws have pins 28 engaging slots 27 or guides in a bar 26 on the piston-rod 25, the spaces above and below the piston 24 being connected respectively by a pipe 41 to a vacuum pump and by a pipe 40 to an air pump on the ship 17, the ship connections between the pipes 40, 41 being reversable. Also extending from the ship 17 are pipes 42, 43, 45 by which, .respectively, (a) water can be pumped into and out of the space between the shells, (b) compressed air can be admitted to the space, and (c) air can escape when water is pumped in. In use, the drum is filled with water and lowered over the object to be raised, the ships being manoeuvred in accordance with instructions telephoned by a person in the diving- bell. The jaws are then closed and air is pumped into and water pumped out of the drum which is then raised by the cables 11, 11a and towed to port. The drum may be fitted with a low-powered engine to drive a screw to make the drum manoeuvrable when in port, e.g. to allow it to enter a dry dock, the engine driving compressed-air and vacuum pumps instead of using the pipes 40, 41, 43, 45.