SECT . x .] OF STEAM NAVIGATION. 313 



Example. If the resistance be equal to 100 horse power, with two engines 



of 50 eadi ; 



the log. 50 = 1-69897 

 2-14438 



3-84335 

 2 



5) 7-68670 

 log. a = log. 34-5 = 1-53734 



Hence, the diameter should be 34*5 inches, and the length of the stroke 

 34-5 x 4 



OF ARRANGING THE PROPORTION OF PoWER FOR VESSELS. 



652. If we now proceed through a calculation of the proportions, and a 

 statement of the conditions to which we ought to attend in arranging the parts 

 of an engine for a vessel, it will form the best illustration of the use of the 

 preceding rules. 



653. The resistance of the vessel should be ascertained for the average velocity : 

 now without pretending to fix the best average, I will suppose this to be 10 feet 

 per second, or 7 miles per hour in still water. 1 Let the length of the parallel part 

 of the vessel be 72 feet, the mean radius of curvature of the ends be 6 half 

 breadths, the breadth at the midship section 25-7 feet, and the girt of that section 

 in contact with water 38 feet. Then the velocity being 10 feet per second, we 

 have by the table, (art. 622.) 



10 s x 38 (-025 x 25-7 + -0032 (72 + 1-05 x 257) ) = 

 10 3 x 36-5 = 36500 Ibs. raised one foot per second, 



or 36500 divided by 550 = 67 horse power nearly. 2 



654. Now if we were to fix on the area and velocity of the paddles for this 

 velocity, it would not be possible to work with advantage against either wind or 



1 This will be equivalent to an average speed of nine miles per hour, where sailing power is to 

 be used in addition. 



* The coefficient -0032 (see art. 614.) is very likely too high ; it is taken from the experiments 

 made by the Society for the Improvement of Naval Architecture, and agrees with the more recent 

 experiments of Col. Beaufoy ; but I am quite convinced that when water is in motion the friction 

 is less, only the exact measure remains to be determined. 



2 R 



