ELECTRIC PROPULSION OF SHIPS. 151 



Mr. Smith mentions that the facts in his table of comparative weights, fuel consumption, 

 etc., show a wide difference from the author's opinions. To substantiate the author's opin- 

 ions, reference is made to the table given above where the facts on which these opinions were 

 based are recorded. Mr. Smith takes exception to the author's statement and places direct 

 Diesel above Diesel electric in regard to reliability. In this coimection, it is interesting to 

 note that present direct-drive Diesels are twin screws. Furthermore, obviously a ship having 

 four engines is more reliable when considered from the "get there" idea than one having two. 

 With a single-screw Diesel electric, the full power of any number of sets can always be util- 

 ized for effective balanced propulsion. This is not the case with any other type of drive. 

 Certainly the control gear of a Diesel electric ship cannot be considered in the same category 

 as the reversing gear of a direct-drive Diesel engine when it comes to complication. All con- 

 trol for a Diesel electric ship is effected through a simple, small-field rheostat which handles 

 only a very small fraction of the total current, and which in going from the full speed ahead 

 to the full speed astern positions, does not even open the circuit. In discussing reserve power, 

 I clearly identified it as reserve power in case of casualty to a prime mover. In comparing 

 the Diesel electric with the Diesel or any other type of drive, the Diesel electric is obviously 

 superior to any of them in this respect. For instance, on a 3-imit Diesel electric, the failure 

 of one engine would only necessitate the loss of 12 per cent in speed, and this cannot be ap- 

 proached by the other drives in case of failure of one of the units, and particularly the direct 

 Diesel. 



It is but natural for some Diesel engine builders to manifest a reluctant spirit in the 

 advocation of high-speed Diesel engines for electric drive, because the net returns to their 

 coffers are naturally going to be enormously reduced. Such recommendations are probably 

 influenced by commercial analysis rather than engineering analysis. However, as a matter 

 of fact, this reluctance might not represent the most expedient commercial analysis, as the 

 manufacture of engines on a large production basis for an advantageous drive would eventu- 

 ally further the sale of engines, and thus result in greater and more profitable business. 



The reason that turbine electric drive is not well suited to destroyers or scout cruisers is 

 because of construction conditions. These conditions do not obtain in battleships and battle 

 cruisers. 



Following Mr. Smith's specifications for the selection of the most suitable drive, I think 

 the analysis as given in the author's paper and reply will clearly show that the electrical 

 apparatus fulfils his requirements which he classifies as the "hard, cold facts." In comparing 

 the turbine electric with double-reduction gears there is very little difference, but what little 

 there is in cost and weight favors the geared turbine. In the author's mind, however, these 

 are not sufficient reasons to eliminate turbine electric drive, particularly in the light of past 

 performance. 



Captain Newman has given a very instructive description of the U. S. coast guard cut- 

 ter Tampa and its propelling machinery. There is one point, however, in the discussion that 

 I would like to clear up, and that is Captain Newman's reference to the writer's allusion to a 

 synchronous motor as being more complicated than an induction motor. Possibly Captain 

 Newman might have meant this for someone else, as certainly the author made no such state- 

 ment in his paper. I did refer, however, to the additional complication of the control in con- 

 nection with synchronous motor drive as compared with the induction motor drive, and I 

 feel quite sure that those who visited ships containing both types of drive will bear me out in 

 this conclusion. 



