A Treatise On The Principles And Practice Of Dock Engineering

FLOATING DOCK AT BERMUDA. 505 connected with the various culverts, so as to serve as air-shafts. Bach of the four sections of the graving docks has a distinct set of culverts for running out and filling in the water, and the pumping arrangements allow of pumping the water out of any one section into any other section, or, through the discharge pit in the rear of the engine-house, into either the main dock or the tidal basin. The machinery at the pumping station consists of four centrifugal pumps, two with fans 5 feet in diameter, and two with fans 4 feet 6 inches in diameter. These are driven by four sets of engines of inverted, direct-acting, high-pressure type, two with cylinders 22 inches diameter and 16j inches stroke, and two with cylinders 17| inches diameter and 16^ inches stroke, for the large and small pumps respectively. The pumps are, together, capable of discharging 650 tons of water per minute into the discharge pit, and, therefore, of pumping out the large pair of docks in about one hour. Two distinct sets of double-acting plunger-and-bucket pumps for drainage, each capable of raising 1,000 gallons per minute into the main dock, are provided. The engines driving them, through gearing, are of the horizontal type. Steam is raised from five boilers, one being spare, of modified marine tubular type, 7 feet 6 inches diameter and 20 feet long, with two flues, 3 feet diameter. The flues lead to wrought-iron chimneys, one for each boiler, and thus an ordinary shaft is dispensed with. Forced draught is driven through the stokeholds by five fans, each with a small independent engine. A cast-iron tank of 250,000 gallons’ capacity, into which water from the drainage culverts is pumped by an auxiliary engine, covers the boiler-house. Floating Dock at Bermuda.* The new dock at Bermuda (figs. 510 and 511) launched in 1902, to replace the former dock of 1868, is from designs by Messrs. Clark and Standfield. It is 545 feet long, with a clear width of 100 feet between the rubbing fenders. The side walls are 13 feet in width, which gives a total width to the structure of about 126 feet. The lifting power, up to the pontoon deck level, is 15,500 tons, but, by using the shallow pound, this can be increased to 17,500 tons. The weight of the hull is 6,500 tons. The sides are high enough to enable a vessel of 32 feet draught to be berthed on the keel-blocks, the latter being 3 feet 6 inches high. The whole structure consists mainly of five parts—three floor pontoons and two side walls. The pontoons supply the chief part of the lifting power, and though the side walls may be used to some extent for the same purpose, their primary object is to give the structure stability and to afford control over the dock in sinking it to take the ship on board. The end pontoons are each 120 feet long and are bevelled in such a way as to facilitate towing. The centre pontoon is 300 feet long. The sides of the pontoons * Vide Engineering, February 14, 1902.