ELECTRIC PROPULSION OF SHIPS. 

 By W. E. Thau, Esq., Member. 



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



in New York, November 17 and 18, 1921.] 



This paper will deal primarily with the electric propulsion of ships, except wherein a 

 comparison of some particular feature or characteristic warrants a reference to some other 

 type of drive. In dealing with electric propulsion, it is necessary to consider all classes of 

 ships, and this leads to two broad, general classifications, such as merchant ships and war 

 vessels. 



MERCHANT SHIP PROPULSIVE EQUIPMENT. 



General Requirements. — The vdtimate purpose of a merchant ship is to earn money. 

 From this standpoint, the factors of reliability, economy, weight, space, cost, operation and 

 maintenance are involved in the propulsive equipment. Therefore the type of drive best 

 suited is that which excels in all or the most important of these factors. The relative im- 

 portance of these items varies with different ships, depending upon the trade route, cargo, 

 etc., with the result that there is a definite and logical field for each of the principal types 

 of drives, such as reciprocating engine, geared turbine, turbine electric, Diesel and Diesel 

 electric. Since many general comparisons of the principal types of drives in regard to these 

 factors have been given in recent articles in the technical press, it is not the intent of the 

 present paper to take up this phase of the subject, but rather to analyze the principal types 

 of electric propulsive equipments and to show in general how they fulfil these requirements. 



Reliability. — The universal use and the indisputable success of electrical apparatus on land 

 is sufficient testimony in behalf of its reliability. The absence of reciprocating parts makes 

 electrical apparatus with its simple rotation as reliable as can be desired. It can almost be 

 said that there are no mechanical troubles with electrical machinery. Broadly speaking, 

 there are no new principles involved in the application of electrical apparatus to ship pro- 

 pulsion. It is true that ship conditions differ from land conditions in certain respects, but 

 there is no phase of the application which presents any really serious difficulty. The most 

 important adverse condition is the deleterious effect of salt and moisture, which is easily 'sur- 

 mounted by proper insulation of the windings and circuits, as is obvious from the several 

 successful years of operation of present electric installations. There can, therefore, be no 

 question as to the reliability of electrical propulsive equipment. 



Economy. — Economy is an important factor and must be given due consideration. To 

 properly analyze this item, it is necessary to consider all equipment involved in the propul- 

 sion with respect to fuel, water, lubricant and supplies. The relative proportions of these 

 items vary considerably in the different types of propulsive equipments. The turbine elec- 

 tric and the geared turbine compare very closel}'^ in economy when all items are considered. 

 The losses in the reversing elements of geared turbines, the losses in the gears and the 

 power required to circulate the additional lubricating oil detract appreciably from the gain 

 which the geared turbine would otherwise have over the turbine electric because of the in- 



