Gadd 



The other way in which viscous effects have been taken account of, the reduction 

 of wetted area by making the sections as nearly semicircular as possible, has 

 been shown to be justified for the present limited purposes of striving towards a 

 purely hydrodynamic optimum. In view of the crude way in which wave resist- 

 ance has been dealt with in the present design, the results encourage the belief 

 that more sophisticated techniques could lead to substantial improvements over 

 current practice. 



FINAL REMARKS 



Part 3 of the paper has left unresolved the doubts raised by Part 2 as to the 

 adequacy of the Inui approach to the relationship between hull form and wave- 

 making. It is possible, but far from certain, that the large differences in resid- 

 uary resistance of the asymmetrical model in the different directions of motion 

 are due to viscous effects. If they are not, then theories, such as the Inui one, 

 for which the relationship between hull shape and source distribution is inde- 

 pendent of the direction of motion must be wrong. If they are, then potential 

 flow theory, even if accurate in itself, must be an unreliable guide to experimen- 

 tal residuary resistance, especially for forms with full afterbodies. In either 

 event, improvements in our present theories are called for. These might take 

 the form of an improvement in the theory for potential flow, and possibly Guil- 

 loton's theory (2) already represents such an improvement. Alternatively it 

 may be more important to take account of viscous effects. 



Despite these uncertainties, there are grounds for hope that considerable 

 reductions of resistance of ship forms are possible. It seems worthwhile to 

 make further attempts to beat the target set in Part 1, without any practical ap- 

 plication in mind, as a means of forging the theoretical tools which will ulti- 

 mately, it is hoped, be useful for practical design, but which, as we have seen, 

 are at present only rather blunt instruments. Moreover, if really radical im- 

 provements on current designs could be demonstrated, this might lead to some 

 practical restrictions, normally insisted upon, being relaxed. Even if, in most 

 practical cases, the form of least possible resistance may not be the shape that 

 should be chosen for a ship, knowledge concerning this purely hydrodynamic 

 optimum must be of assistance in making a correct technical assessment of 

 ship design. 



ACKNOWLEDGMENT 



The work described above was carried out in the Ship Division of the Na- 

 tional Physical Laboratory, and is published by permission of the Director of 

 the Laboratory. 



REFERENCES 



1. Inui, T., "Wave-Making Resistance of Ships," Soc. of Naval Architects and 

 Marine Engineers Trans. 70:283 (1962) 



728 



