Engineering Wonders of the World
Volume I

THE PROPELLING MACHINERY OF A SHIP. 41 Fig. 16.—the Mauretania’s ” boilers ready to go on board. increased earning power of the vessel; but in the larger vessels there would be little or no increase in such cost. This combination of piston engines and tur- bine is now being put to practical test in the new cargo steamer Otaki, of 7,430 tons, which The “Otaki.” left Messrs. Denny’s shipbuild- ing yard in November 1908. This vessel is fitted with two sets of triple- expansion piston engines, driving twin screws fitted in the ordinary fashion ; but between these two engines is installed a low-pressure turbine of very large size. The steam, after having done its work in the piston engines, instead of entering the condenser directly, is passed through the turbine, which drives a centre screw, so that the vessel has in all three screws. The turbine revolves in one direction only, the turbine-driven screw being used solely for propulsion ahead, and change-valves are fitted so that the steam may be passed from the piston engines either directly into the condenser or to the turbine. Hence, in manoeuvring, the vessel is to all intents and purposes an ordinary twin-screw ship. The Otaki is virtually a sister ship to the Orari, the boiler installation of both vessels being identical ; but the Orari has only two sets of piston engines. On the first-named vessel’s trials an average mean speed of 15’09 knots was obtained, while the average speed of the Orari under similar conditions was 14’6 knots. The combination in the Otaki therefore showed greater efficiency, and it is anticipated that the improvement indicated on the trials will be maintained during the sea work of the vessel. Increased Speed result- ing from the Combination.