Application of Wavemaking Resistance Theory 



a prismatic coefficient of 0.64 showed that the C^ value of this model at 

 V/VT :z 1.1 is almost the same as that of a Taylor's Standard Series Model with 

 the same beam-draught and displacement-length ratios, but with a much smaller 

 prismatic coefficient value of 0.59. 



Another point mentioned in Professor Weinblum's comment is related to 

 the viscous drag which is much more complicated than wave drag. Our knowl- 

 edge of viscous drag as functions of the hull form may be almost nil from the 

 scientific viewpoint. But for practical ship design, it may not be a too difficult 

 task to shape a form with a constant volume such that its viscous drag can be 

 kept within reasonable limits. Besides these formulae quoted by him, there are 

 thousands of models having been tested at Froude number ranges where the 

 wave drag is very small in comparison with the viscous drag. Additional prac- 

 tical information as to the reduction of viscous drag of ship hulls may be ex- 

 tracted from this source. 



DR. EGGERS 



Dr. Eggers' comment is very interesting. It is indeed true that for a given 

 body in infinite fluid there are many possible singularity distributions to repre- 

 sent that body. But for a given singularity distribution, we have a quite differ- 

 ent situation. In this case, we should determine the body correctly by including 

 the free-surface effects. Since such procedures are very time consuming, a 

 double model technique has been used in the paper. Then the logical question is, 

 how much difference is there between these two bodies so obtained. Such differ- 

 ence depends upon the singularity distribution under consideration. As mentioned 

 in the paper, if it disturbs the free surface very little, such difference would 

 also be little. Since we are interested in singularity distributions which produce 

 very small free-surface distributions, we may not need to be too seriously con- 

 cerned with the point raised by Dr. Eggers. In the meantime, we are consider- 

 ing the possibility of tracing the streamline by including the free surface effect. 



DR. NEWMAN 



Dr. Newman points out that a ship of low wave resistance will satisfy the 

 linear free surface condition, but not necessarily close to the ship. Since the 

 wavemaking resistance depends on the far field free surface disturbance only, 

 it would be interesting to know, in such case, to what extent the local disturb- 

 ance influences the accuracy of the computed wavemaking resistance. 



In general, when we deal with ship- shape forms such a situation is not 

 likely to occur. Professor Inui and his students in Tokyo University have com- 

 puted many wave profiles along the side of ships. The local disturbance seems 

 to be always much smaller than the free wave disturbance. 



1151 



