The Mechanical Handling and Storing of Material

330 THE MECHANICAL HANDLING OF MATERIAL smooth, the sheet anchor serving efficiently as a compensator, and maintaining a perfect tension on the endless conveying cable. The principle of the “Miller” conveyor, as used on the U.S.S. “ Marcellus,” is shown in Figs. 469 and 470, but when tested at sea it actually had an additional rope above the conveying ropes which was led astern, terminating in a sheet anchor. This device is now called the Marine Cableway. It is intended to be utilised by ships stationed at a distance of from 350 to 500 ft. apart. It might possibly work successfully at a greater distance, but such an experiment has not yet been tried. The vessels are connected by an ordinary cable, and the towing vessel gets under way at a speed ranging from 4 to 8 knots per hour, according to the condition Fig. 469. General Arrangement of Spencer Miller’s Plan for Coaling at Sea. of the weather and the sea which is running. A speed of 5 knots in moderately rough water has been found sufficient to keep the cableway taut and to maintain the proper distance between the craft, unless a tide or some unusual current is encountered. The appliance which has been fitted to the “Marcellus” may be described as follows :— Fig. 470. Details of Spencer Miller’s Plan for Coaling at Sea. An engine, with double cylinders and double friction drums of special design, is placed just abaft the foremast of the collier. It has two steam cylinders 12 by 12 in. A f-in. diameter steel rope is led from one drum over a pulley at the mast-head, and thence to a pulley at the head of shear-poles on the warship, and returned to the other drum. The engine moves in the same direction all the time, and tends to wind in both strands of the conveying rope. A novel form of load carriage is suspended from this rope. It is provided with a gripping device on the upper strand and wheels to run on the lower strand. This carriage conveys two loaded bags, weighing 420 lb. each, suspended from a bail, which hangs in a hook below the carriage. A hoist takes the bags from the deck, lifting them to the mast- head, while the conveyor carriage, coming in from the mast-head, locks itself under the bail. As soon as the bail is released by a man under the trestle-trees, the engine operator hauls in the lower parts of the conveyor line. The upper part of the conveyor line is therefore drawn from the rear drum, slipping the specially contrived friction devices. Thus the carriage passes from collier to ship, the tension being sufficient to ensure the bags clearing the water between the vessels. The rope is drawn in at a speed of 1,000 ft. per minute, and if the points of support— mast-head and shear-head—do not vary, the upper strand will be drawn out, under tension of about 3,000 lb., at the same rate of speed. If, however, the distance is increased during the transit of the load, the extra rope called for is given by the slipping of the upper part from the drum. This increases