ENGINES, MARINE. I. TYPES or ENGINES.— Tile Tr/pie-Ed-pa RiOn Eflgii/P.—Fig. 1 represents the latest type of triple-expansion engines used in the high-speed twin-serew 'Brit ish cruisers Thetis, Terpsichore, and Tribune. They were built. by James, & George Thomson, of Glasgow. In the design the makers have obtained over 13 indicated borse-power per ton weight f machinery in working oilier. with water in boilers and condenser•.
The engines are of the triple-expansion vertival inverted type. Each set of engines is placed in a separate engine-room with a fore-anil-al•t bulkhead dividing them, and each is in all reslier•ls exactly similar. The cylinders are 331, 49, and 74 in. in diameter•, respeetively, with :I stroke of 3 ft. 3 in. Each cylinder is made of an entirely independent casting. and are connected by steel stay-rods securely attached to each casting. To still further inerease I heir stability the (.0111nm-heads have stout cast-steel struts fitted in hot \Yvon them. The reeviver,V011Si.4 entirely of copper pipes. The while of the cylinders an. steam-jacketed. The working barrels of the high-pressure and interinediAte-pressure cylinders are Of forged steel, lint those or the low-pressure cylinder are of specially hard. close-grained cast iron• 1'iston-v.1v,- working in separate liners are fitted to the high-pressure and intermediate pressnre cylinders., and the low-pressure cylinder has a flat. double-ported slide-valve with it special type of relief ring at the heck. Ralence-cylinders are fitted to the valves of all the cylinders, to reduce the strain on the valve-gear as far as possible. The valve-gear is of t he (111111)14.-PPIPIlt HI% link-motion type, all joints having exgel,B,umNv large surfaces. A double cylinder reversing-i•ngine is (irovidial. and the reversing shaft-levers are fitted with screw•-gi-ar to allow of the expini,ion in each cylinder being altered independently of the others. The back columns are of east steel, with separate pinned-on faces for the guides, and the front columns are of forged steel, thus giving a clear view from the starting platforms which are arranged in the wings of the ship.
To insure the desired lightness, the main condensers, which have a collective cooling sur face. of 10,000 sq. ft., have casings and ends built up entirely of naval brass plates riveted together. The steam is condensed outside the tubes, and the circulating water passes through them, and is supplied by two large 14-in. Gwynne centrifugal pumps, the discharges from which are connected by an athwart-ship pipe having sluice-valves at each end, and also in the middle, where it passes through the longitudinal bulkhead. The crank and propeller shafts are hollow, of fluid-compressed steel, and the crank-arms are cut away as much as possible for lightness and convenience in fitting the centrifugal lubrieators for the crank-pins. The thrust blocks and collars are of cast steel ; the latter are lined with white metal and are of the horse shoe type, each separately adjustable. The screw-propellers are three-bladed, and with the bosses and all connections are of gun-metal.
The exhausts from the whole of the auxiliary machinery in the ship are led into an auxil iary exhaust-pipe which is connected with two auxiliary condensers, each of which has its own air and circulating pump entirely independent of those for the main condensers. The com bined cooling surface of the two auxiliary condensers is 1,000 sq. ft. In addition to the afore mentioned auxiliary machinery there are in each engine-room a set of air-compressing engines and reservoirs, electric-light engines and dynamos, a Weir main-feed pump with patent auto matic regulating gear, two bilge and fire pumps, a small pump for the drain-tanks, and two evaporators and distillers, each having independent steam-pumps.
Steam at 155 lbs. pressure is supplied by five steel return tube-boilers, three of which are double-ended, 13 ft. in diameter by 18 ft. 6 in. long, and two single-ended, 13 ft. in diameter by 9 ft. 7 in. long. The total grate-surface is 573 sq. ft., and total heating surface 15,104 sq.