Gadd 



used. However the experimental results also raise questions as to the extent of 

 viscous effects on wavemaking resistance. These questions will need to be sat- 

 isfactorily answered (perhaps by a modification of the wavemaking theory on the 

 lines suggested by Guilloton (2)) if the theoretical approach to design is to be- 

 come much more accurate. 



PART 1 - CRITERIA FOR LOW RESISTANCE 



Waveless Bodies 



Optimum ships in the sense defined above would be expected to have a low 

 wavemaking resistance. This does not mean that the only requirement is to 

 minimize wavemaking, which for a given displacement and speed could doubt- 

 less be done by making the ship resemble a rowing eight. This would, of course, 

 lead to an excessive wetted area and a correspondingly high friction drag. For 

 deeply submerged bodies, with no wavemaking, experience suggests that a 

 streamlined airship shape, of length to diameter ratio in the region of 5 to 7, is 

 best. For such a body of revolution, a suitable equation for the radius r as a 

 function of the distance x from the nose is 



where L is the body length. If the maximum thickness position is 40 percent of 

 the length back from the nose, n = 2/3, and, as can be seen from Fig. 1, the 

 body has a well streamlined shape. It is then easily shown that the displace- 

 ment volume V and the surface area s are given by 



V = 0.439t2L^ (1) 



and 



S = tL^ (2.168 + 0.946 t^) , 



where t , the ratio of the maximum diameter to the length, is assumed to be 

 small enough for ds = dx[l+ (dr/dx)^] ^''^ to be replaced by dx [i+ (1/2) (dr'dx)^] . 

 Hoerner (3) suggests that for turbulent boundary -layer flow the drag coefficient 

 c^^, based on wetted area for such a body, is related to the corresponding flat- 

 plate friction coefficient Cp by 



Fig. 1 - Body of the form 



r = A(xA-)^'^ [1- (x/L)] 



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