ELECTRIC PROPULSION OF MERCHANT SHIPS. 



By W. L. R. Emmet, Esq., Member of Council. 



[Read at the twenty-seventh general meeting of the Society of Naval Architects and Marine Engineers, held 



in New York, November 13 and 14, 1919.] 



The use of electricity for propelling ships was first advocated in the case of 

 large warships in which it affords particular advantages in the matter of cruising 

 economy through change of speed ratio, interchangeability, space distribution, etc. 

 The first application, however, was made in the case of the U. S. collier Jupiter, 

 which is in most features a ship of the merchant type. The demonstration of 

 geared-turbine propulsion came after the first serious proposals of electric drive, 

 and the advantages which have been attributed to the geared method have sus- 

 pended such activities as were considered in this country in the direction of electric 

 drive for merchant ships, while, in the case of warships, electric drive activities 

 have been uninterrupted. In the meantime certain electrically driven ships built 

 in Europe, operated with very high degrees of superheat, have shown wonderful 

 fuel economy, and many more such ships are being equipped. 



The larger American shipbuilders, having their own facilities for machinery 

 construction, have, not unnaturally, been opponents of electric drive, and the Emer- 

 gency Fleet Corporation, which for some time has represented ownership, has for 

 various reasons discontinued such activities in this direction as had been planned. 



Two or three years ago the writer was of the belief that the geared equip- 

 ments then being made afforded a solution of the problem which in cost and results 

 would probably prevent commercial success of electric drive in merchant ships, 

 although it was realized that the margin of possible advantage was small. Since 

 that time improvements in electrical designs have been developed, and limitations 

 of gear possibilities have appeared which put the question in a different light, 

 and it is now the writer's belief that electric drive is justified in all large ships and 

 that it will very soon develop a wide application, notwithstanding the great efforts 

 of skill, organization, and capital which have been given to the introduction of the 

 gear drive for vessels of all classes. 



The discussion of this subject is largely a matter o± comparison with other 

 methods, and the purpose of this paper is to make clear what is proposed in a 

 specific case and to suggest comparisons which may affect relative value. 



The case selected is that of a vessel of 8,800 deadweight tons, length 424 

 feet, beam 54 feet, having a cubic capacity of 460,000 cubic feet and capable of 

 making 11.5 knots with 2,500 shaft horse-power delivered to a propeller operating at 

 100 revolutions per minute. Plates 116 and 117 show an electric propelling equipment 



