ENGINEERING PROGRESS IN THE U. S. NAVY. 53 



On Plate 3 1 are given the indicated horse-power speed curve of the Dela- 

 ware and the shaft horse-power speed curves of the North Dakota, Utah, and 

 Florida. 



In comparing these curves it should be noted that, due to differences in 

 displacements and in appendages, the effective horse-power required to give 

 the Delaware a speed of 21 knots will give the Florida and the Utah 20.82 

 knots, and the North Dakota 21.1 knots; at 12 knots for the Delaware, the 

 equivalent speed of the Florida and the Utah is 12.17 knots and of the North 

 Dakota 12.1 knots. 



Assuming that shaft horse-power is approximately 92 per cent of indi- 

 cated horse-power in large, well-designed reciprocating engines, and reducing 

 the indicated horse-power of the Delaware to shaft horse-power, the following 

 table of comparison results: — 



Delaware. North Dakota. Utah. 



Speeds of equal K. H. P.' s 21 21.1 20.82 



I. H. P. for this speed 23,400 



S. H. P. for these speeds 21,528 27,150 25,000 



Propulsive coefficient equals (per cent) 



S. H. P.-f-S. H. P 71.76+ 56.8+ 61.8 + 



Cruising speeds of equal F. H. P 12 12. i 12.17 



I. H. P. for this speed 3,600 



S. H. P. for these speeds 3,312 3,825 3,975 



Propulsive coefficient equals (per cent) 



F.H.P.^S.H.P 74+ 64.1+ 61.6 + 



While the Florida curve is shown on Plate 31, that vessel is not included 

 in the above table, as the weather conditions during her standardization trials 

 were unfavorable and the efficiency of the propellers fell off greatly, due to 

 these adverse conditions. This excessive falling off in efficiency of propulsion 

 under adverse conditions of wind, sea and of ship's bottom are characteristics 

 of turbine-driven vessels, and affect requirements (a) (b), and (c) to a large 

 degree. 



Formerly, the favorite method of comparing the relative economies of 

 propulsion of reciprocating engines and turbines was by comparing the water 

 per shaft horse-power of the turbines with the water per indicated horse- 

 power of the reciprocator, in this comparison all mention of the large differ- 

 ence between the indicated horse-power required in the one case and the 

 shaft horse-power in the other being carefully neglected. 



The method of comparison in use to-day is the commercial one of 

 "pounds of fuel per knot" at different speeds, and it is on this basis that the 

 curves shown on Plate 32 are constructed. 



