RESISTANCE OF BILGE KEELS. 



17 



quired to overcome the frictional resistance of the keels. This is equivalent to as- 

 suming a hull efficiency of unity for both the bare hull and the hull w^ith 9-inch 

 keels attached. Plausible assumptions concerning the effects of bilge keels on 

 wake gain and thrust deduction might make appreciable changes in the differences 

 here chosen as the basis for conclusions; but it has been considered best to abstain. 



Table III. 

 Power for Bilge Keels. 



The horse-powers required to overcome the friction of the 9- inch bilge keels 

 have been computed by the equation 



//{=o.ooT,oj VRi 



and set down in column 10, and the ratios of columns 9 and 10 are given in col- 

 umn II. From this last column it appears that the power required to drive the 

 bilge keels is two and a half to three and a half times that computed from the 

 friction of the keels. The ratio is therefore more than twice that found from the 

 thrust of the shaft on page 15. The discrepancy cannot be charged to error or 

 uncertainty of observation or computations, but is presented as a real difference 

 of results from our two methods of investigation. 



