ELECTRIC PROPULSION OF SHIPS. 145 



In connection with the flexibility of the series system of Diesel electric propulsion, Mr. 

 Thau points out the simplicity of the speed control which is obtained by varying the generator 

 field strength; this method can be combined with that of variation of motor field strength so 

 as to give the most efficient operating condition for any of the various combinations of motors 

 and generators. 



President Capps : — Owing to unavoidable absence of the author, who cannot be here 

 until tomorrow afternoon, paper No. 8, which was to have been read tomorrow morning, will 

 be read by Mr. Bailey, the author, tomorrow afternoon, taking the place of paper No. 12, 

 by Profesor Hovgaard. 



Mr. Pierce : — In view of the fact that there has been considerable discussion relative to 

 the Diesel electric drive, I might say that we are all familiar with the specifications sent out 

 for a tender on a ship for Diesel electric. The Diesel electric equipment for that ship was 

 58 per cent heavier, 20 per cent more fuel consumption, and 10 per cent more cost than the 

 direct Diesel. 



President Capps : — It is hoped that in making their replies, the authors of the papers 

 will be able to throw more definite light on the subject of weight of machinery and fuel con- 

 sumption, because the differences per shaft horse-power, when translated into terms of cargo 

 capacity, or fuel which can be carried, are very important indeed. If there is no further 

 comment, we will bring the discussion on these papers to a close. 



Mr. Emmet : — As to the question of the relative economy, the turbine being the same 

 for both, the difference must be small. In a large ship, for which we have recently designed 

 electrical transmission machinery, we would only lose 4.5 per cent. The San Bonito, which 

 just came over, and which ran in the Mediterranean for a long distance, had a rate corre- 

 sponding to 1 pound of fuel per shaft horse-power. Any of these other electric ships will 

 do pretty nearly that. The difference is, in any case, small, provided the turbine is equally 

 good. I have tested a large number of ship gears by actually running them on generators at 

 a given load, and I have actually found the efficiencies of a double reduction ship gear as low 

 as 96. I have tested 6,000 horse-power gears and two 3,000 horse-power gears, and know 

 the losses are considerable in the gears alone. 



I think it quite probable that Mr. Anderson's criticism of the 100 R. P. M. propellers 

 in the Shipping Board boats equipped may be correct, although, when these jobs were under- 

 taken, statements to the contrary were given us by the best authorities. 



Mr. Thau : — Before replying to the discussions which have been made on my paper, 

 I desire to take this opportunity to extend my appreciation and thanks to the authors of the 

 discussions for the thorough manner in which they have gone into the subject. The majority 

 of the points brought out in the discussion are very beneficial to the progress of the art. 

 There are, however, a few instances where the meaning of the author's statements in the 

 paper have been misconstrued, and also some instances where some of the discussions have 

 digressed from the points at issue in the paper, in an endeavor to discuss claims for electric 

 propulsion systems which have been made in other articles in the technical press. It is hoped 

 that the interested persons reading the paper, the discussions and the author's reply to the 

 discussions will take these points into consideration. 



