The Mechanical Handling and Storing of Material

UNLOADING VESSELS BY BARGE OR SHIP ELEVATORS 469 that the driver has a good view of the hatchway in which the elevator is working. The switchboard is in the cabin as well as the other gear in connection with the electric installation. The whole is so well arranged that one man can take the elevator out of one hold, travel to another hold, and start work again without any assistance. The guaranteed capacity of each elevator was 100 tons per hour, but from the first that quantity has been considerably exceeded, 120 tons being easily handled. During the first few weeks of working, several cargoes of grain amounting to over 40,000 tons were discharged most satisfactorily. As an instance of quick dispatch it may be mentioned that a cargo of 7,500 tons of wheat was discharged in less than five days. The installation was built by Amme, Giesecke, & Konegen, of Brunswick. There are no practical reasons why installations similar to the foregoing should not be mounted on pontoons and thus be converted into floating barge elevators, as the mechanical arrangements are practically identical with those of the floating Mitchell cantilever elevator described later. FLOATING ELEVATORS OR MARINE LEGS Floating Derrick Elevator.—The derrick elevator erected for the late London Grain Elevator Co., now absorbed into the Port of London Authority, is the invention of Mr A. H. Mitchell, engineer of the old company. This derrick unloading elevator is shown in Fig. 650, which represents it ready to be lowered over the ship’s side for unloading purposes. It has been designed for unloading grain from the largest types of American liners engaged in the grain trade (such vessels as the “Minnehaha” and sister ships of the Atlantic Transport Co.) into lighters for conveyance into other coasting vessels or into warehouses. The first elevator of this type was built by Spencer & Co., Ltd., of Melksham. The whole plant consisted essentially of four parts. Firstly, the pontoon; secondly, the travelling car, containing the engines and the various driving gears; thirdly, the support, consisting of lattice girders and shear legs; and fourthly, the elevator itself, which is lowered into the ship’s hold. The pontoon is built of steel, and is 75 ft. long by 24 ft. wide, and has a draught of 8 ft. It is square at the bow so that it can be brought close to the side of the vessel which is to be discharged. The deck of the pontoon is specially strong, and is fitted with a track, the rails of which run from bow to stern, and are 7 ft. apart. The travelling car moves on these. There are two vertical boilers in the stern, one being sufficient to drive the plant, the other only being used in case of emergency. Ample bunker space is allowed amidship. The pontoon is self-propelling by means of a small marine engine and a pair of screw propellers. The space in the hold not required for bunker purposes is filled with ballast to ensure the stability of the vessel. The trolley, which is 17 ft. long by 9 ft. wide, rests on the rails on six wheels. The range of its motion from end to end is 36 ft. It is conveyed backward or forward by a pair of wire ropes which are fastened at one end to the pontoon and at the other end to the drums of the winches. The engine, which is in the centre of the trolley, is a 30 H.P. of double-cylinder type, and is connected with the boiler by flexible pipes, the connection being made in the centre of the revolving drum in such a way that the piping rolls itself on or off the drum as the trolley moves backward or forward. The large lattice girders of the derrick shown in the illustration are carried on trunnions on the forepart of the trolley, while the main shaft, which drives the elevator