Pien 



.30 



,50 



.60 



Fig. 8 - Theoretical c ^ curves of 

 M(^,0 = ^» 4/3^^, 7/3^^ , respectively 



are chosen to give a proper balance between the viscous and wave drag, rather 

 than for optimum viscous drag. 



Knowing how to keep the wave drag at a low level, as previously described, 

 we can select principal dimensions without the danger of increasing wavemaking 

 resistance materially. This fact immediately opens the way to reducing the 

 wetted surface. 



As an example, let us consider Model 4210 of Series 60, It was designed 

 for v/yr = 0.9 and has the following characteristics: 



L/B =7.5 



B/H =2.5 



A/(L/100)' 



122 . 



Assuming the length to be reduced by 20 percent, and the displacement and ship 

 speed kept the same, V//L becomes about unity and A/(Laoo)^ becomes 190.6. 

 The reduction in wetted surface is of the order of 16 percent. For this model, 

 such a change in length will greatly penalize the performance, the increase of 

 wave resistance being much greater than the gain in viscous drag. If, based on 

 theory, we can design a hull form of these proportions and displacement, with 



1124 



