ELECTRIC PROPULSION OF SHIPS. 143 



In that ship the drive is by means of a synchronous motor, and one speaker particularly re- 

 ferred to the question of the racing of electric motors when the propeller of the ship was out 

 of the water. We had very heavy seas — at one stage of the crossing we ran into a hurricane, 

 and the propeller was out of the water over and over again, and there was no racing whatever 

 — the motor stood up perfectly to its work, and I believe that with a properly designed syn- 

 chronous motor, you will get, in addition to high efficiency, equally good results as with any 

 other type of motor. 



Mr. E. a. Stevens, Jr., Member (Communicated) : — Before discussing this paper in 

 detail, T think it would be well to consider the question of transmission in general, whether it 

 be electric, mechanical gear, or hydraulic. The only advantage of any of these is the ability 

 to run the main machinery at a dififerent speed than that of the propeller, thereby obtaining 

 greater economy than Avhat would be possible if the two were operating at the same speed. 

 With this in view, the Diesel electric (excpt in a few special cases) would be eliminated. As 

 the Diesel engine is more reliable as well as more economical at the lower speeds, it is far 

 better to connect direct to the propeller than to use any of the transmissions mentioned above. 

 It has been argued that when the cylinders reach a certain size trouble occurs. This can be 

 eliminated by increasing the number of cylinders up to eight to one shaft, or by the use of twin 

 or even triple screws. When the power required is greater than what would be practicable 

 with three screws, it would be better to use steam, as the weight, first cost, and complications 

 of the Diesel electric system would ofifset any advantage, if any, that this system would have 

 in economy. 



Mr. Thau states : "The economy of a reciprocating engine drive is obviously poorer than 

 that of a properly designed turbine of either type, for the reason that the reciprocating en- 

 gine cannot utilize the same expansion of steam." This is true for high powers, but for a 

 slow ship of 3,000 horse-power or less, the reciprocating engine has shown as good economy 

 as the average geared turbine and better than the electric drive, in spite of the fact that no 

 superheat was used with the engine while 50 degrees superheat was used with the geared tur- 

 bine and 180 degrees with the electric drive. The cost of the electric drive outfit installed is 

 over double that of the reciprocating engine, while the geared turbine is about the same or a 

 little less than the latter. 



The horse-car driver who became a motorman and the steam locomotive engineer who 

 became an electric locomotive engineer cannot be classed with the marine engineer, as neither 

 the motorman nor the locomotive engineer does his repair work or keeps his machines in 

 condition. These men are merely drivers. All the repair work and care of the apparatus are 

 done by the repair gang or rotmd-house foreman. 



If three junior engineers are required for the direct-connected Diesel as shown in the 

 table on page 1 10, why are they not required for the Diesel electric, which is more complicated ? 



The fact that the U. S. Navy has adopted the electric drive for battleships and battle 

 cruisers speaks well for it, but cannot the same thing be said about the geared turbine which 

 is being used by the British Admiralty in the above-mentioned classes ? 



The protection against torpedo attack afiforded by the electric drive is not much greater, 

 as the motors on the outboard shafts are as near the skin of the ship as the geared turbine 

 would be; besides, the ship fitted with the latter could be better protection against gun fire 

 as machinery is lighter, while the maneuvering ability of the geared turbine is all that is 

 desired. 



