ENGINEERING PROGRESS IN THE U. S. NAVY. 75 



power ahead, and at 80 per cent of the full-speed revolutions, the backing horse- 

 power of the Nevada will be about 55 per cent of that developed at full speed 

 ahead. Since a great deal more steam can be passed through the turbines than is 

 possible with the engine, this can be increased at least fifty per cent so that a 

 backing power as high as 70 or 80 per cent can be obtained, for short periods — 

 as long as the boilers can furnish the steam. 



The President: — The discussion is still open. Mr. Emmet! 



Mr. William L. R. Emmet, Member: — In the discussion of methods of pro- 

 pulsion I want to take an annual opportunity of saying a word for the electrical 

 method. In the last few months we have tested the generating unit for the collier 

 Jupiter, which is being built at the Mare Island Yard, and we have obtained from 

 that unit the exact result which I predicted on it, which was considerably better 

 than what we guaranteed on the ship. During its construction, however, we learned 

 some things about turbines, and I arrived at the opinion that we could get very 

 much better results by certain changes. So we decided to rebuild the turbine, 

 retaining the high-pressure portion of that which we already had, and putting on a 

 new low-pressure end. This new machine was tested last week, and it has given 

 the best economy of any engine ever produced for any service. With only 5,000 

 kilowatt output we produced 72 per cent efficiency with steam having 100 degrees 

 of superheat. The water-rate of the Jupiter, with 190 pounds pressure, saturated 

 steam, and 28.5 vacuum, will be 11. 2, which I think is about 2.5 pounds better 

 than the best reciprocating-engine drive under such conditions. 



This machine, instead of having so many rows of blades, and other elabora- 

 tions such as have been spoken of here by Mr. Curtis, has only ten rows of blades, 

 and the length of its group of wheels is only about five feet, and their diameter is 

 about the same. It is an extremely small thing, any part of which can be handled 

 and got at, it is extremely simple, and its parts are large and rugged. In compar- 

 ing methods of propulsion, all that I insist upon is that due attention should be 

 paid to the characteristics incident to the best propeller speeds and also to the char- 

 acteristics incident to the best turbine speed. This new turbine of the Jupiter is a 

 high-speed machine, which runs at 2,000 revolutions per minute, and it is a very 

 distinct advance in prime movers over anything ever produced before. The merit 

 incident to the best propeller speed and also the merit incident to such a turbine 

 should be carefully weighed as against the characteristics of other prime movers 

 of different speeds and resultant propeller characteristics. With electrical pro- 

 pulsion we select the best propeller speed, and there is a great difference in economy 

 due to the best selection, as we all know, and as has been shown on the floor of this 

 meeting. The question is : How shall we get these best speeds, and what can we 

 afford to sacrifice in order to obtain approximations to them? With certain types 

 of turbines you can produce very good results if the speeds are not too extremely 

 low, that is, with certain improvements of speed in the existing marine turbine you 



