BULLETIN OF THE UNITED STATES FISH COMMISSION. 147 

 THRUST OF THE SCREWS. 



The net power applied to the propulsion of the hull by the two pro. 

 pellers being- 289.042 horses is equal to (280.G42 x 33,000 =) 9,558,186 

 foot pounds of work per minute, and the speed beiug 10.03 knots per 



, /10.03XG08G \,^,„onn4' ^ • X ., ^ 



hour IS equal tcf .... - = 1 101^376 feet per minute; therefore 



the resistance of the hull and the equivalent thrust of the screws at 



that speeed was ( ^^Tr. ,,J^^ = J 9395 pounds. The thrust per indicated 



(9395 \ 

 ^^y'rj26"= ) 20.31 pounds, and per 



(9395 \ 

 iO lO 97 ~ y ^'^^ pounds. 



POWER ABSORBED BY THE FRICTION OF THE WETTED 

 SURFACE OF THE HULL AGAINST THE WATER. 



Taking the resistance of the water to a square foot of smoothly 



painted iron of the surfaces of the hull moving at a velocity of 10 feet 



per second to be 0.45 of a pound, and (according to the method of Chief 



Eugiueer Isherwood, United States Navy) deducing from the speed of 



the vessel the mean speed of its immersed surfaces due to the inclination 



of the water lines there results a speed of 16.3507G feet per second, and a 



consequent surface resistance of (10^ : 0.45 : : 1G.3507G^ :) 1.2030G3 pounds 



per square foot at that velocity. The aggregate wetted surface during 



the above-mentioned voyage was 7,350.44 square feet, and the power 



, ,. ,. . / 7350.44 X 1.2030G3 X 1G.35070 X GO \ 

 expended in this resistance was I oo .>,>/> = I 



202.893 horses; consequently of the 289.G42 horses power required to 



(2G2.893 X 100 \ 

 ~^S^07'4>> — ~ / ^^-^^ P^^ cent, was expended in 



overcoming the friction of the hull on the water, and the remaining 

 9.27 per cent was expended in displacing the water and overcoming the 

 pressure of the wind against the upper part of the hull, the spars, and 

 the rigging. 



THE CHANGE IN THE CRANK-ANGLE. 



The cranks, as originally arranged, at 145 degrees, diminished, to a 

 small extent, the friction on the center main bearings by the almost op- 

 posite position, and almost opposite crank efibrt. The indicator dia- 

 grams taken from the high-pressure cylinders bear a very near resem- 

 blance to each other, with the cranks at either angle, but in the low- 

 pressure diagrams the difference is marked. 



Fig. C is from the starboard low-pressure cylinder with the cranks at 

 145 degrees. 



