ELECTRIC PROPULSION OF SHIPS. 125 



land lately, and trials were made at 15 knots, the maximum speed at which low-speed con- 

 nection can be nm. At that speed the oil consumption was 10 per cent lower; and the 

 water consumption, as reported to me, was 7 per cent lower with the low speed connected 

 than with the high, and at lower speeds than that there is, of course, a greater gain. In a 

 warship this is a very important matter. 



Mr. Charles F. Bailey, Member of Council: — I feel sure that the Society appreciates 

 the excellent and comprehensive paper presented by Mr. Thau. 



This discussion and investigation has been prepared in an impartial spirit with the pur- 

 pose of emphasizing a few of the outstanding facts and conditions apparent in a comparison 

 of the following types of marine propelling machinery, including Diesel electric and steam 

 electric-driven machinery, as covered in Mr. Thau's paper. Let us consider the following : 



Group I. 2,000 S. H. P. 



(A) Diesel electric, twin screw. 



(B) Direct Diesel, twin screw. 



(C) Single-reduction geared turbines, single screw, oil fuel, Babcock and Wilcox boilers, 

 also Scotch boilers. 



(Di) Triple expansion reciprocating engine, single screw, oil fuel, Babcock and Wilcox 

 boilers, also Scotch boilers. 



(D2) Triple expansion reciprocating engine, twin screw, oil fuel, Babcock and Wilcox 

 boilers, also Scotch boilers. 



Group II. 2,600 S. H. P. 



(A) Diesel electric, single screw. (Fig. 1, Plate 16.) 



(B) Direct Diesel, twin screw. (Fig. 2, Plate 17. 



(C) Geared turbines, single reduction, single screw, oil fuel, Scotch boilers, also Bab- 

 cock and Wilcox boilers. (Figs. 3 and 6, Plates 18 and 21.) 



(D) Quadruple expansion reciprocating engine, single screw, oil fuel, Scotch boilers, 

 also Babcock and Wilcox boilers. (Figs. 4 and 6, Plates 19 and 21.) 



(E) Turbine electric machinery, eclipse type, single screw, oil fuel, Scotch boilers, also 

 Babcock and Wilcox boilers. (Figs. 5 and 6, Plates 20 and 21.) 



Babcock and Wilcox boilers for installations (C), (D), (E), Fig. 6, Plate 21. 



These comparisons are based on merchant marine requirements. Small powers have 

 been selected as more data for comparisons are available, and as installations of such powers 

 would be practicable with each type of machinery. 



It has been the endeavor to make the comparisons as carefully and fairly as would have 

 been the case if they had been estimated upon for a proposed order. 



The ratio of shaft horse-power to indicated horse-power is assumed as follows : Diesel 

 electric, 0.65; direct Diesel, 0.72; reciprocating engines, 0.92. 



The installations of Group I are smaller than would usually be adopted in merchant ser- 

 vice, but the comparisons will hold fairly closely. The information from which these com- 

 parisons were made was largely taken from detailed estimates and are closely approximate. 

 The principal elements of each installation are tabulated in Tables I and II from which it 

 will be noted in Table I covering Group I and Table II, covering Group II, comparisons are 



