PROGRESS IN MARINE CONSTRUCTION GRACIE. 693 



The turbine, having proved its worth in the reahn of high power 

 and fast steaming, was boldly adopted by the Cunard Co. in the 

 Lusitania and 3Iawetania, built in 1907. These vessels surpassed all 

 others, with a length of 760 feet, 88 feet of beam, and 60^ feet depth 

 of girder. The girder ratio was thus aboiit 12^, and for the first time 

 high-tensile steel was utilized in the upper member to meet the 

 higher stresses. Some lightening of structure was thus obtained. 

 These ships were the first mercantile vessels to have four lines of 

 shafting, and practically the whole of the vessel's length was occu- 

 pied by boilers, machinery, and fuel. About 68,000 horsepower was 

 developed, and an ocean speed of between 25 and 26 knots regularly 

 maintained on an expenditure of about 5,000 tons of coal per voyage. 

 Although already surpassed in dimensions, these two vessels retain 

 their supremacy in speed unchallenged. 



In 1908 a further step was taken with a view to securing a greater 

 reduction in steam consumption per efi^ective horsepower. This con- 

 sisted in the combined use of the reciprocating steam engine and 

 turbine in order to retain the low speed of revolution of the recipro- 

 cating engine, with its accompanying favorable propeller efficiency, 

 while at the same time effectively utilizing the expansion of the steam 

 to the condenser pressure. The first ship to be thus fitted was the 

 Otaki, a vessel of 464 feet in length and about 9,900 tons dead weight 

 capacity ; and a comparison of this ship with a sister ship fitted with 

 ordinary twin-screw quadruple-expansion engines showed a differ- 

 ence of about 20 per cent in steam consumption per effective horse- 

 power in favor of the combination type of machinery. 



The system is principally suited to vessels of fairly large power, 

 moderate speed, and for service on long voyages. The usual practice 

 has been to fit the reciprocating engines on the wing shafts, and 

 the exhaust turbine on a center shaft, an arrangement being made 

 for exhausting the steam from the reciprocating engine direct to the 

 condenser, and thus cutting out the turbine during maneuvering. 

 Combination machinery, as compared with all reciprocating machin- 

 ery, involves more complexity and cost, and a slight increase of 

 weight in the engine room; but the improved economy realizable 

 allows of reductions in the boiler capacity and in boiler room and 

 fuel weights, which more or less compensate for this. The influence 

 of the last item is dependent on the length of voyage. 



In 1911 a length of 850 feet was reached in the White Star liner 

 Olympic. This luxurious vessel measures 852 feet by 92 feet by 64 

 feet, and has a speed of 21 knots with 46,000 horsepower combination 

 machinery driving three screws. She carries 735 first-class, 674 second- 

 class, and 1,026 third-class passengers, and has the following public 

 rooms : Gymnasium, reading and writing room, lounge, smoke room, 

 veranda and palm court, restaurant, reception room, dining saloon, 



