The Mechanical Handling and Storing of Material

UNLOADING VESSELS BY BARGE OR SHIP ELEVATORS 471 structure at its supports is formed of two pitch pine shear legs in the bow, one on either side, and a lattice steel back leg which is about 50 ft. long. These shear and back legs are connected together at the top by a steel pin and collars, the back leg being hinged to the trolley and the front legs to the deck of the pontoon. All these parts can readily be raised to any angle, allowing perfect freedom for the trolley to move backward and for- ward on deck. The. elevator is supported by a jib which is binged to the back leg, as shown in the illustration. On this jib is fitted a band conveyor 2 ft. 6 in. wide, which is necessary, as the elevator itself dips deep down into the ship’s hold, and the grain may have to be conveyed up or down to reach its destination. Just below the jib on the other side of the back leg extends a cantilever (also fitted with a band conveyor) projecting over the stern of the pontoon, at the end of which are two long shoots for the delivery of the grain. The buckets are- 20 in. wide, and of the continuous type, similar to those illustrated in Figs. 15 and 16, page 19. 'Phe elevator is 53 ft. long, and has a vertical range of 18 ft., and when in its highest position the head is 90 ft. above the water level, and has a clear 40 ft. between the elevator well and the water level. This is necessary to reach over the side of large ships. It can discharge grain from a ship with a 40-ft. beam and a hold 45 ft. deep. The driving Fig. 651. Fig. 652. Fig. 653. Diagrams showing Development of Mitchell’s Cantilever Grain Elevator. power required is 20 B.H.P. and the capacity is 150 tons per hour, and this can be kept up provided the trimmers can keep pace with it. These elevators are in use at the Victoria and Albert and also at Tilbury Docks. The elevator can be housed very neatly when out of use, in which case it lies flat upon the deck, and the delivery shoots are drawn in, so as not to project over the sides of the pontoon. The position of the shear legs is then approximately at an angle of 35° to the deck. The expeditious way in which the marine leg can be set to work may be gauged from the test in which it was lifted over the bulwarks of a ship 30 ft. 6 in. above the water level, lowered into the hold to a depth of 43 ft., and started to work delivering grain in seven minutes. The Mitchell Cantilever Grain Elevator.—This is the best known and most efficient type of a floating apparatus which can unload a cargo of grain from the largest ocean-going steamer. As its development may be of interest, it is fully given here. It is, of course, only proposed to deal, in these introductory remarks, with the general arrangement for manipulating the machine, as the elevator itself presents no new features. The earliest type was constructed as shown in diagram, Fig. 651. It consists essentially of a self-contained elevator suspended from a balanced rocking jib supported at the top of a stationary lattice steel post. The objection to this construction lies chiefly