314 OF STEAM NAVIGATION. [SECT. x. 



current ; besides there is a disadvantage in large paddles at sea, which is greater 

 than the loss by varying from the maximum. Hence, I would recommend to 

 arrange the paddles for a velocity about one foot per second greater than the 

 average rate. Consequently, (art. 631.) IP x -75 x b h = the power of the 

 paddles; and as the resistance is 36500, we have 



:pp ^H = b h = 36-6 feet, the area of the paddle boards. 



Again, suppose the radius of the wheels to be four times the depth of the 

 paddles, then by the second equation of art. 631. we have, 



2-25rxll 3 xftA 9xll 3 x36-6 O QQ 11, j r 



- 3 - i - = - w - = 62633 Ibs. raised one foot per second, 



fi T A / 



or 62633 divided by 550 =114 horse power nearly. 



655. As the vessel requires 114 horse power, if we have two engines, each will 

 be 57 horse power; and (art. 651.) 



log. 57 = 1-75587 

 2-14438 



3-90025 

 2 



5) 7-80050 

 log. diameter = 1-56010 



or the diameter = 36-32 inches; the length of the stroke four-thirds of the 

 diameter, or 48-43 inches ; and consequently (art. 336.) the number of strokes per 

 minute will be 25|: hence, (art. 641.) corrected for the depth of the paddle, 1 

 we have, when the velocity is 11 feet per second, or 7-5 miles per hour, 



24^ = 24 x 7-5 ? .j f 

 25-5 25-5 



for the radius of the wheels ; and dividing it by 4 gives the depth of the paddles 

 1*8 feet. But in order to reduce the breadth of the wheel, it is better that they be 

 made 2 feet, and the radius of the wheel 7-3 feet ; the paddles will then be 2 feet 



1 For when the depth is one-fourth of the radius, V = 3 r v = ^-^, instead of <LY 



2r d 1 2 ' 



hence, !L : : : 21 : 24. 

 2 7 



