188 THE APPLICABILITY OF ELECTRICAL PROPULSION TO 



finger. The engine-room watch required for a battleship would be just half what it 

 would be with other means of propulsion, as one engine-room would be idle prac- 

 tically all the time. In a rough sea there is no racing, with its attendant strains 

 on machinery and on the personnel on watch. Any desired speed can be very 

 quickly attained. The speed can be very accurately maintained and without any 

 effort on the part of the personnel. These last two points are of very great im- 

 portance on battleships when maneuvering in formation. The stand-by qualities 

 are also superior to those of other installations, for at a very small expense in 

 the way of steam, the main turbine can be kept running very slowly and the en- 

 gine-room is then ready to answer signals at any time ; this might be of great im- 

 portance to a battleship. The backing qualities of this installation are also superior 

 to other forms, particularly turbine installations. It is possible to attain full power 

 in the astern direction. 



Economy. — In considering the question of economy, we have reached the point 

 which first suggested the use of electricity for the purpose of propulsion. None 

 of the older forms of propulsion, such as reciprocating engines or direct-connected 

 turbines, can compare at all favorably with this method, the gain in economy being 

 over 20 per cent both at high and cruising speeds. The only other method of pro- 

 pulsion that would appear to compete with this method in economy would seem to 

 be the combination of high-speed turbines and reduction gears. The loss in the lat- 

 ter amount to about 2 per cent, while in the electric reduction gear the losses are 

 from 8 to 9 per cent. Mechanical reduction gears have been developed to a high 

 degree, and it is very probable that in quite a number of cases the mechanical gears 

 would be preferable to the electric drive, but as this paper is limited to a discus- 

 sion of battleships that subject will not be touched. 



For battleships I do not believe there is any question of the relative economy 

 of the two methods — the electric drive is far superior. The electric reduction 

 method possesses two inherent advantages that the mechanical method cannot 

 overcome. First, the electric installation uses only one turbine at low powers; 

 second, the induction motors are fitted with pole changers which allow the turbine 

 to be run at normal speed with the ship cruising at low speed — in other words, the 

 electric drive permits of two speed reductions while the mechanical gear has only 

 one. These two advantages exist no matter how the two installations may be laid 

 out, and they far outweigh the difference in the losses of the two methods. To 

 show just how great these advantages are, two curves are shown. Plate 70 shows 

 the Jupiter's turbine operating under varying loads and Plate 71 shows the turbine 

 operating under varying speeds (and also loads). The load curve does not really 

 show how very bad the conditions are for a battleship, as in that case the power 

 at 12 knots is only about one-seventh what it is at 21 knots and the curve shown 

 does not give so great a per cent of reduction. It will also be seen that the speed 

 curve is very steep at the low speeds and shows the bad effect of reducing turbine 

 speed very greatly. As nearly all the cruising of a battleship is done at fairly low 

 speeds, it is evident that the electric drive will be more economical than the mechan- 

 ical gear. 



