75 



Calculations have been checked by experiments for three bodies of 

 revolution over a range of medium Proude numbers (up to 0.42) . ■'^■'•'' The quanti- 

 tative agreement was not satisfactory for F = 0.26, and some unexpected shift 

 of phase was found between calculated and measured resistance curves. However, 

 a first orientation as to the relative properties of different models can be 

 obtained even for the case f = b, i.e., when the backs of the bodies touch 

 the surface. Generally, a closer agreement is found between computations and 

 experiments for submerged than for surface ships as regards the form of humps 

 and hollows in the resistance curve. Some astonishing results were found: 

 For Instance due to pronounced Interference effects at some Froude numbers 

 >0.35 the total resistance of a full body (fli= C = 0.80) is lower than that 

 of a very fine one (^ = C = 0.5^6) having the same principal dimensions but 

 some 30 percent less volume. ■'■■'■" 



One must be cautious in applying results obtained from blunt bodies 

 like a sphere or circular cylinder to elongated bodies. For the former the 

 speed V = Vgf is a critical value since the resistance curve has a maximum 

 value at that speed (comparable to the case of finite depth h); hence, the use 

 of a Froude number P-. = v>ff is advisable in plotting results. But resistance 

 curves of bodies having ratios of slenderness comparable to those of ships, 

 a/b '^ V'^' do not show any peculiarity at v = Vgf; therefore the dimension- 

 less number F- = v/Fgf cannot be recommended when investigating the resistance 

 at constant immersions. On the other hand the parameter v/V^ is appropriate 

 when investigating the resistance as a function of the immersion. 



Finally, reference may be made to the problem of bodies of least 

 wave resistance. It was mentioned that results are similar to those for sur- 

 face ships, but peculiarities of form are still more pronounced. For a given 

 Proude number the optimum form varies slightly with the depth of immersion. 

 Figure 37 indicates the shape of some forms derived under rather special con- 

 ditions. In the light of the remarkable qualitative agreement between calcu- 

 lation and experiments it appears legitimate to develop optimum forms by 

 calculations. 



So far no attempt has been made to treat bodies having blunt noses, 

 which cannot be represented by a line distribution. 



