Application of Wavemaking Resistance Theory 



many fruitful ideas. A general programme of research into low resistance hull 

 forms is now being undertaken at N.P.L.; this includes experiments to examine 

 Pien's suggestion that the double model approximation should give closer agree- 

 ment between calculated and measured resistances for source distributions hav- 

 ing low wave resistance than for resistful forms. Two bodies are being designed 

 from wave source theory, each consisting of a bow shape followed by a long par- 

 allel afterbody, and an attempt will be made to measure their head resistances 

 alone. One of these forms does not have a particularly low calculated wave re- 

 sistance, but the second has been optimised following the same general princi- 

 ples as those adopted by Pien. If good agreement between theory and experi- 

 ment is obtained for this second form, we believe that it will aid significantly in 

 using wave source theory as a practical design tool in the way indicated in this 

 paper. 



The assessment of the results of any such study of calm water resistance 

 effects depends on the establishment of a recognised yardstick or resistance 

 criterion. In assessing wave resistance alone, this criterion should preferably 

 involve only the displacement, speed and length. Displacement and speed are 

 the primary specified operational requirements, and length may be regarded as 

 a primary limiting parameter. The hydrodynamic criterion of quality should be 

 based on the maximum immersed length, thus imposing a penalty on a device, 

 such as a projecting bulbous bow, which reduces resistance at the expense of 

 increased underwater length. Not all comparisons have been made on this basis 

 and it is more than possible that this has influenced the conclusions drawn from 

 them. 



DISCUSSION 



S. W. W. Shor 

 Bureau of Ships 

 Washington, D.C. 



In commenting on Dr. Pien's paper I first wish to congratulate him on the 

 persistence with which he has pursued his search for a practical solution to the 

 problem of reducing the total resistance of a ship's hull. The fact that this 

 search seems verging on a successful result with even more general applicabil- 

 ity than we had dared hope is most gratifying. 



As to the details of his paper, I wish to invite attention particularly to two 

 of his statements which are corroborated by my own work. 



First, Dr. Pien is quite correct that the best approach within the confines 

 of existing ship wave theory is to optimize the shape of the forebody of the ship, 

 and then to design the stern separately. This means that he does not count on 

 using the stern waves to cancel the bow waves, but instead sees to it that the 



1145 



