74 ENGINEERING PROGRESS IN THE U. S. NAVY. 



results may come out a few per cent one way or the other, but even if they should 

 fall short of expectation by say 5 per cent at full power, or 10 per cent at low power, 

 such a possibility can hardly justify discarding the decided advantages of the 

 turbine due to its full-power efficiency and its greater overload capacity and reli- 

 ability, nor can it justify, it seems to me, the discouragement and set-back in turbine 

 development in this country which is bound to result if the next battleship is 

 equipped with engines. 



In my judgment, the best form of propelling machinery for the next United 

 States battleship would be straight turbines either in a two, three, or four shaft 

 form, combined with small cruising geared turbines, which would be used only at 

 low power, and on long cruises where economy was important. AVhen these were in 

 use the steam would pass first through the geared turbine, and then through the 

 main turbines. A very large gain in economy, at least 25 per cent, can be had 

 in this way at speeds in the neighborhood of 10 or 12 knots. The horse-power to 

 be transmitted by each gearing would probably not exceed seven or eight hundred, 

 and the art of turbine gearing has already reached a stage where the practical suc- 

 cess of such an arrangement in a battleship is reasonably well assured. In England 

 over 100,000 horse-power of geared marine turbines are built or building, and in 

 this country a considerable number of geared turbines are now in operation, driving 

 electric generators, and a much larger number are building. If any objection 

 should be found to the geared turbines in service, they could be dispensed with, 

 and the ship would still be a better proposition, all things considered, than if she 

 were equipped with a reciprocating engine. 



Holding Power of the Propellers. — I entirely agree with Captain Dyson that 

 in all previous turbine vessels the propellers used have been altogether too small, 

 and the result has been that in adverse conditions of wind sea, or of ship's bottom, 

 not only does the efficiency fall off materially at high power, but the sUp of the 

 screws becomes so great that their holding power is quite inadequate. In our last 

 battleship, the Nevada, arrangements have been made to use propellers having a 

 disk area about 18 per cent greater than those of either the North Dakota or the 

 Utah. I would, however, strongly advise using still larger propellers turning at a 

 still slower speed. This would involve some loss in turbine efficiency, but it would 

 be almost entirely made up by a gain in propulsive efficiency, so that the net result 

 would be but little inferior to the present arrangment. Probably the difference 

 would not exceed i or 2 per cent at full power and 3 or 4 per cent at 10 knots. 

 This would give a much better and more manageable ship under all conditions, not 

 only in going ahead but in backing. On a ship like the Nevada, I should advise 

 using propellers at least 40 per cent larger in disk area than those used on the North 

 Dakota, and turning at not over 200 revolutions per minute for full power. 



Backing Power. — The backing power, or, more properly speaking, the efficiency 

 of the turbines when backing, has in the case of the Nevada been largely increased 

 over that of the North Dakota, so that this ship will undoubtedly be an entirely 

 different proposition in this regard. With a steam flow equal to that used at full 



