Data for Ships of Minimum Resistance 



improvement was substantial and has not been realized. Unfortunately, for the 

 present purpose, the reasons are not clear-cut and one cannot ascribe the failure 

 entirely to unreliability of the linearized theory in a situation where it predicts 

 unusually small values of the wave resistance. As has already been mentioned, 

 there was, in fact, remarkably little disturbance of the free surface at and near 

 the design Froude number, so that a small value of the residuary resistance 

 might have been expected. It seems possible that the contribution of the observed 

 boundary -layer separation behind the stern bulb to the residuary resistance may 

 have increased this so much that the favorable wave -resistance properties of 

 the hull were lost. With the wisdom of hindsight it seems evident that for our 

 first symmetric model we should have chosen the one designed to be optimum 

 for y^ = 6 (Fr = 0.289) or 7^ = 9 (Fr = 0.236) instead of /^ = 5. Their Michell 

 wave resistances are negligible in the Froude number range 0.2 to 0.3 (see 

 Fig. 1) and their maximum waterline slopes at the stern are smaller, about 16° 

 and 11°, respectively. 



Even thovigh the two computer-designed ships have not shown any marked 

 superiority in resistance qualities, there is another sense in which the attempt 

 to let certain over-all requirements and the optimization procedure design the 

 ship can be said to have been successful. All forms have been designed without 

 aid of the naval architect's practiced and expert eye and yet the two tested ones 

 have performed as well as the equivalent Taylor's-Series hulls. This in itself 

 is encouraging and seems to indicate that it is worth the trouble to refine the 

 method, in particular, to devise computational procedures for taking into account 

 more complicated kinds of restraints. 



SYMBOLS 



R^ Total resistance 



Rj Frictional resistance 



R^ Residuary resistance 



Rjj Wave resistance according to Michell 



Cp Prismatic coefficient 



Cg Block coefficient 



Cy Volumetric coefficient = V/L^ 



C Area coefficient = SL"^C„"'^ 



S ¥ 





1059 



