694 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



racquet court, swimming bath, and Turkish baths. Each of her finest 

 suites consists of sitting room, two bedrooms, bathroom, and clothes 

 rooms, and occupies 800 square feet or 160 square feet per person ac- 

 commodated. 



To-day the largest vessel afloat is the Imperator, 880 feet by 90 

 feet by 63 feet. Her girder ratio is 10.7, and she has eight decks above 

 her water line. With boilers of the Yarrow type and turbines of 

 62,000 horsepower driving four shafts, she has an ocean speed of 

 22| knots. She carries 900 first-class, 800 second-class and 2,700 

 third-class passengers, with a crew of 1,200, or 5,400 persons in all. 

 Her accommodation is the latest word in spaciousness and luxury. 

 For first-class passengers there are two large and three smaller dining 

 saloons, restaurant, grillroom, ladies' room, ballroom, winter garden, 

 smoke room, gymnasium, swimming bath, and Turkish baths, the total 

 area given up to public rooms being 36,000 square feet, or about 40 

 square feet per passenger. She has 446 first-class staterooms, includ- 

 ing 12 suites, the average number of persons per room being thus 

 practically two, and the average room area 80 square feet per person. 



In the all-turbine installation for the merchant service the turbines 

 have been mostly of the compound type — ^that is, with the steam pass- 

 ing through two turbines in series — the usual arrangement being a 

 three-shaft one, having one high-pressure turbine and two low-pres- 

 sure turbines, with the exhaust from the high-pressure turbine pass- 

 ing through the two low-pressure turbines in parallel. Only in some 

 few cases has a twin-screw arrangement been adopted — that is, with 

 the high-pressure turbine on one shaft and the low-pressure turbine 

 on the other — ^but a similar arrangement, duplicated, has been applied 

 to many of the largest installations, both naval and merchant, by 

 fitting two independent sets, of two turbines each, working on four 

 lines of shafting. With a view to improving the steam economy in 

 the all-turbine system, a further development has been introduced in 

 some recent ships of large power having a four-shaft arrangement, by 

 passing the steam through three turbines in series. The steam passes 

 through the high-pressure turbine to the intermediate-pressure tur- 

 bine, and then through the two low-pressure turbines in parallel, 

 there being one turbine on each line of shaft. The result of this is 

 that for the same overall length of each turbine unit (a matter of 

 some practical moment) the steam passes through a greater number 

 of rows of blades and a condition of improved efficiency is gained, 

 while a reduction of the blade leakage is obtained, due to the rela- 

 tively greater length of blade as compared with the alternative two- 

 series design. The improved turbine-efficiency resulting from this 

 arrangement thus increases the range of speed at which an all-turbine 

 set can successfully compete with the reciprocating engine. Several 

 ships with turbine machinery of this three-series type have lately 



