A Treatise On The Principles And Practice Of Dock Engineering

SLIPWAY HAULAGE. 541 supported from the deck by a tower, and has a diameter of 10 feet with a height of 16 feet. It is coned at the bottom, and furnished with connec- tions for two or three pipes, through which the grain is drawn with the current of air from the hold of the ship. An automatic air-lock is attached, and through it the grain discharges itself into the hopper of the weighing machine, whence, after weighing, it is directed into a barge in bulk or is filled into sacks. This type of machine is also in use at Bemerhaven and Hamburg. In a pneumatic apparatus employed at Limerick, the grain, instead of flowing away in bulk, finds its way through a second air-lock into a chamber below the deck into which air is forced at a pressure of from 6 to 8 Ibs. per square inch. From this a pipe passes upwards, bends over the elevator’s side, and is there connected, by a piece of flexible hose, with an underground pipe passing up into and along the roof of a warehouse. By means of outlets provided at convenient intervals the grain is discharged into the required bins. Slipway Haulage.—As originally devised by the late Thomas Morton, the inventor of the slip dock, the machinery for hauling vessels up the ways consisted of spur gearing worked by manual power, horses, or the steam engine. Hydraulic apparatus was introduced about the year 1850, and has since existed through various stages of development in competition with a form of winding apparatus originated about the year 1879. The hydraulic apparatus in its later form, as contrived by Messrs. Lightfoot and Thomson,* consists of three main hauling rams (figs. 562 and 563), connected by means of an upper crosshead with a single reversing ram under constant pressure, and by means of a lower crosshead with a double set of hauling links which extend nearly to the extremity of the ways, resting upon wings cast uponj the centre rails and being guided thereby. The action is as follows : —By the admission of water to one or more of the main cylinders, according to the size of the vessel being dealt with, a forward stroke of 10 feet is made against the constant pressure of the reversing ram. The main cylinders are then opened to exhaust, and the backward stroke is made under the action of the reversing ram. There is a dual system of pawls on the cradle, so arranged that one of them engages in the rack of the permanent way at the end of each forward stroke, while the other engages in the joint plates of the hauling links at the completion of each backward stroke. During the backward stroke, therefore, the cradle remains stationary upon the ways, while the hauling links are passing downwards to take up a new position 10 feet behind the pawls in which they were previously engaged. With this system, no disconnection or removal of links, such as obtained in earlier types, is required. The return stroke is made much more rapidly than the forward stroke on account of the much smaller area of the ram. * Lightfoot and Thompson on “Slipways for Ships,” Min. Proc. Inst. C.E., vol. Ixxii.