72 ENGINEERING PROGRESS IN THE U. S. NAVY. 



turbines for the new North Dakota under exactly Uke conditions except at lower 

 revolutions. It also shows the per cent gain in efficiency of the new North Dakota's 

 turbines. 



Plate 43 shows the number of heat units necessary to furnish the steam used 

 by the turbines of the North Dakota and the engines of the Delaware. These 

 curves are obtained by taking the actual water required by the main engines alone 

 and multiplying by the total heat in the steam taken between the hot-well tem- 

 peratures and the initial temperatures. The auxiliaries in this comparison have 

 been expressly excluded, because it so happened that in the case of the North 

 Dakota the official trials were made with fewer auxiliaries than was the case with 

 the Delaware. In order to make a fair comparison, therefore, it is necessary either 

 to exclude the auxiliaries or to assume an equal auxiliary consumption in both 

 cases. I have thought it simpler to exclude them. 



The third curve on Plate 43 shows the heat units that would be required by 

 the turbines of the new North Dakota operating under the same steam conditions 

 as the old North Dakota. This curve is obtained by multiplying the product of 

 the water-rates and the shaft horse-powers for the new North Dakota by the same 

 heat values as in the North Dakota. That is, the curve for the new North Dakota 

 is based on the same initial steam conditions and same hot-well temperatures as 

 the curve for the North Dakota, and the improvement shown is due partly to the 

 gain in turbine efficiency and partly to the gain in propeller efficiency. The 

 improvement in propulsive efficiency has been assumed to be ten per cent at all 

 speeds. At the bottom of Plate 43 is a curve showing the per cent excess heat units 

 required by the Delaware over the new North Dakota. 



It will be observed that the Delaware at 21 knots requires 18 per cent more 

 heat units than the new North Dakota, at 18 knots 12 per cent more, at 16 knots 5 

 per cent more. Below 14 knots the consumptions are practically equal. 



This means that the new North Dakota could either have her boilers cut down 

 15 per cent, or her turbines could develop 18 per cent more effective or push horse- 

 power with a given amount of steam. Allowing for an auxiliary consumption 

 equivalent to that of the Delaware, this increased horse-power would give the ship 

 an increased speed of one-half knot. In practical working, however, the turbine, 

 because of the fact that it can safely be forced much higher above its normal capa- 

 city than the engine, can utilize more steam and can therefore develop a great deal 

 more horse-power. With such a steam-generating capacity as our battleships are 

 now provided with, the turbine ship could be driven at least a knot and probably a 

 knot and a half faster. In this connection, I draw attention to the "Scientific 

 American" of November 16, which states that the British battle-cruiser Princess 

 Royal in her recent trials showed a mean speed over the measured mile of 33 knots, 

 and a speed of 32 knots on the eight-hour full-power trial. This is 4 knots above 

 the designed speed. This ship has a displacement of 26,300 tons, about the same 

 as that of our last battleship, but is somewhat longer, being 660 feet. 



Whether these curves are trustworthy or not depends, of course, upon whether 



