154 ELECTRIC PROPULSION OF SHIPS. 



country, as far as economy is concerned. I am quite sure, however, that the concession must 

 be given to electric drive when considering flexibiHty, both of arrangement of apparatus 

 and reserve power in case of casuahy to prime movers. There are other reasons substantia- 

 ting electric drive which have been covered in recent articles in the technical press. 



Mr. Anderson makes the inference that a geared-turbine drive, particularly for merchant 

 ships, should show better- steam consumption than a turbine-electric drive, and requests in- 

 formation on the performance of existing electric-drive cargo ships. I regret that I do not 

 have authentic figures in these cases. It would seem to me, however, that with the turbines 

 operating at the same speeds and other things being equal, or at least comparable, that geared- 

 turbine drives should show a slightly better economy. The value of this small difference is 

 questionable. Personally, I think there are other features of greater concern than a slight 

 difference in efficiency. The figures which Mr. Anderson quotes for the electric drive of ex- 

 isting cargo ships seem to me to be rather high and out of proportion for the figure he quotes 

 for the geared-turbine drive. At best, I cannot see more than 5 or 6 per cent difference. 



I do not propose to reply further to the discussion regarding the selection of twin and 

 four-screw ships and electric and geared drive, as this is a matter that concerns the Navy De- 

 partment. 



All the maneuvering that I have witnessed, particularly as concerns backing, has been 

 done with all the engines in use at the time, and I know of no ruling to do all such reversing 

 on only one machine. As far as I can see, there is no reason for it. 



I do not agree at all with Mr. Stevens in his analysis of Diesel electric drive as given 

 in the first paragraph of his discussion, and a reference to previous paragraphs of the 

 author's reply to discussion will clearly show the reasons why I do not agree with him. 



Referring to the second paragraph of Mr. Stevens' discusion, his statements regarding 

 the comparable economy of the reciprocating engine in sizes of 3,000 horse-power or less do 

 not agree with any figures that have ever come to my attention, and reference to Mr. Bailey's 

 table of comparison will also show that both triple-expansion, single-screw, and triple-ex- 

 pansion, twin-screw engines consume 16 per cent and 27 per cent respectively more fuel than 

 the single-reduction geared turbine in the case of a 2,000-S. H. P. drive. Mr. Bailey also 

 gives a fuel consumption of 6 per cent more for a quadruple expansion reciprocating engine 

 in the case of a 2,600 horse-power drive. 



The writer's reference to the horse-car driver who became the motorman, etc., was 

 merely done to show the little difficulty that electrical apparatus had in replacing other means 

 of motive power on land. As far as repairs to electrical machinery aboard ship are con- 

 cerned, owing to the reliability of such apparatus, there is nothing likely to occur that cannot 

 be taken care of by an ordinary electrician, and furthermore, I do not believe the marine en- 

 gineer would want to place himself in the position of saying that he could never learn to 

 repair an electrical machine, as this would indicate that the height of progress for marine 

 engineers was already attained. Also, due to the simple construction of electrical apparatus, 

 repairs should be very infrequent. 



The matter of electric drive and geared drive for war vessels and the manner in which 

 the different layouts affect the protection of the ship, etc., have been covered in many pre- 

 vious articles, and a discussion of it will, therefore, not be entered into at this time. Mr. 

 Stevens asks why I neglected to mention that, while battleships and battle cruisers are to be 

 fitted with electric drive, the light cruisers and destroyers are being equipped with geared 

 turbines. A reference to the fifth paragraph of the paper under the section of "War Ves- 



