Pien 



2. the theory based on the linearized free-surface condition is more accu- 

 rate when the level of the wavemaking resistance is very low (disregarding the 

 value of beam) and when a higher order of ship surface condition approximation 

 has been made. In such a case, the linearized free-surface condition is suffi- 

 cient even though the ship-surface condition must have a higher than first-order 

 approximation for practical beam values. Therefore, Inui's approach is both 

 logical and practical even though it may seem inconsistent. 



The second defect in the existing theory is that the viscosity effect has been 

 neglected. At the present time there is no reliable method of estimating this, 

 and the existing theory cannot predict the wavemaking resistance of a given hull 

 form accurately. However, this fact should not prevent us from using the theory 

 to search for forms with good wavemaking resistance qualities. The statements 

 may seem to be self- contradictory, but it is hoped to show in what follows that 

 they are quite consistent. 



Because, for practical purposes, the viscosity effects can be neglected on 

 the forebody and because the linearized free- surface condition will always over- 

 estimate the wavemaking resistance, we can use the theory to compute the upper 

 limit of the wavemaking resistance of a forebody alone. This is equivalent to 

 that of an infinitely long prismatic form fitted to the after end of the forebody. 

 Since the forebody contributes most of the wavemaking resistance, the capability 

 of the present theory to predict the upper limit of the forebody wavemaking re- 

 sistance immediately gives the theory a very important role in the search for 

 hull forms with low resistance. 



The most frequent use made of the theory in ship design problems is to op- 

 timize the wavemaking resistance of a whole ship without checking the forebody 

 free-surface disturbance alone. It is conceivable that the optimum value so ob- 

 tained might be attributable not to the fact that both the bow and stern produce 

 very small free waves but rather to the favorable theoretical interference effect 

 of large bow and stern free-wave systems. Due to the viscosity effect, the ex- 

 isting theory cannot accurately predict either the amplitude or the phase of the 

 stern free waves, so that the favorable interference effect as predicted by the 

 theory may not always be realized in practice, thus leading to a large wavemak- 

 ing resistance. Therefore, it is rather important to minimize the forebody free- 

 surface disturbance. 



It will be shown later that by proper application of the existing theory, we 

 can obtain hull forms with theoretical wavemaking resistance values much less 

 than those of existing designs. Due to these low levels of wavemaking resist- 

 ance, such theoretical predictions will be quite accurate, any remaining errors 

 no longer being of great practical significance. In concluding this section, I 

 feel that the present wavemaking resistance theory can and should play an im- 

 portant role in the design of future ships. 



1114 



