Engineering Wonders of the World
Volume I

THE PROPELLING MACHINERY OF A SHIP. 33 Fig. 6.—BABCOCK AND WILCOX MARINE TYPE BOILER WITH CASINGS AND MOUNTINGS COMPLETE. {Photo, Messrs. Babcock and Wilcox, Limited.) boilers which have been installed in large warships are the Niclausse and Dürr; while for torpedo-boat destroyers and small craft a number of varieties, due to Thornycroft, Nor- mand, Reed, White, and others, have been adopted. The rate of combustion of the fuel, and hence the power developed by a boiler, can be increased greatly by the adoption of forced draught, by means of which a Forced better supply of air is brought Draught. > , 6 to the furnaces than is possible with only the natural draught caused by the funnel. Forced draught is specially valuable in warships, as it permits the development of large power and high speed in case of emer- gency with the smaller size and weight of machinery suitable for ordinary speed under (1,408) natural draught. The system adopted in the British navy is known as the “ closed-stoke- hold ” system (Fig. 7). With this arrange- ment the stokeholds are made air-tight, and filled with slightly compressed air by means of fans. Another well-known system is that due to Mr. James Howden of Glasgow, which has been very extensively adopted in the mercantile marine. In this case the air supply from the fans is first heated by passing it over a series of tubes containing the waste gases on their way to the funnel. It then goes into a reservoir, from which the supply (under pressure) to the ashpit and over the fires is regulated. Since the quadruple-expansion engine repre- sents the latest word in the piston type of marine engine, we propose to deal with it somewhat fully. Fig. 8 is a front view of an up-to-date set ^he Quad- r j i • x > ruple-expan- oi quadruple engines, erected . „ . ° sion Engine. in the shops of the North- Eastern Marine Engineering Company of Wallsend, ready to be fitted on board the steamer Royal Prince, of 5,547 tons. This en- gine takes steam at 220 lbs. pressure from four boilers, and indicates about 3,500 horse-power. The following are the diameters of the four cylinders : high pressure, 24| inches ; first inter- Fig. 7.—DIAGRAM SHOWING THE PRINCIPLE OF THE FORCED DRAUGHT IN STOKEHOLD. mediate, 35 inches ; second intermediate, 51 inches ; and low pressure, 74 inches. The piston stroke of all four cylinders is 51 inches. Read- ing from right to left in our illustration, or from VOL. II. 3