ELECTRIC PROPULSION OF MERCHANT SHIPS. 279 



tons, and there will be an additional weight saving in the machinery itself since 

 the electrical equipment will weigh about 9 tons less than the engine equipment for 

 such a ship. 



Economy. — If this equipment is operated with 200 pounds steam pressure, 200° 

 F. superheat, and a vacuum of 28.5 inches, the steam consumption per shaft horse- 

 power hour, not including auxiliaries, will amount to 9.5 pounds. Under normal 

 conditions at sea, with most of the auxiliaries driven electrically, this should give a 

 steam consumption for all purposes not greater than i r pounds per shaft horse- 

 power hour. Such a steam consumption will require at least 30 per cent less fuel 

 for all purposes than would be required by a good reciprocating engine equipment 

 operating without superheat, and even if an equal superheat were used with a 

 reciprocating engine equipment, the gain would still be over 20 per cent. 



In this connection it must be considered that large numbers of American ships 

 are now being equipped with reciprocating engines and without superheat, although 

 it has been amply demonstrated abroad that the use of high superheat is practical 

 and economical. 



If such a ship were in operation 250 days in a year between California and 

 Australia, burning fuel oil at $1.00 per barrel, the saving in fuel over a similar 

 engine-driven ship operating without superheat would amount to about $17,000, and 

 the increased freight capacity leaving California would amount to 585 tons, which is 

 7^ per cent of the deadweight tonnage. 



Reliability. — A study of the records and uses of such electrical apparatus as 

 is applied in this case will show that the equipment is less liable to interruption of 

 service than any other form of single-screw equipment which is applied to vessels. 

 With such an equipment, however, arrangements could easily be made by which the 

 ship could be navigated about half speed with the main generating unit out of serv- 

 ice. This could be done by providing a motor-generator set or rotary converter so 

 arranged that the power of auxiliary generating units could be delivered to the 

 main motor. In an electrically propelled ship, electricity is produced simply for one 

 definite purpose, and the arrangement is simpler and more reliable than shore appli- 

 cations where power is taken from large distributing systems. It is also possible to 

 provide automatic means which, by interrupting excitation, guard against the pos- 

 sibility of serious damage through possible accidents or insulation failures. Such 

 electrical apparatus of the type used in ships is very easily repaired, and, even when 

 damaged, can generally be temporarily connected so as to be operative. The knowl- 

 edge necessary for such repairs is very easily imparted and is constantly being 

 practiced in our industries by persons who have had little or no electrical training. 



Reliability of Gearing in Ships. — To make comparison of such an equipment 

 with a gear-driven ship is much more difficult, since a great variety of arrange- 

 ments of turbines and gears have been applied to ships of this type. In the matter 

 of reliability, as has been said, the electrical equipment is entirely beyond ques- 

 tion, while many evidences of serious trouble and deterioration have developed in 

 geared ships of most types which have been produced. Gears have been very sue- 



