AN APPROACH TO THE DESIGN OF 

 LOW-RESISTANCE HULL FORMS 



G. E. Gadd 



Ship Division, National Physical Laboratory 



Feltham, Middlesex, England 



SUMMARY AND INTRODUCTION 



This paper is divided into three parts. The first seeks to establish criteria 

 for judging what is meant by a hull form of low resistance. The task of a ship 

 is seen as that of carrying a given load at a given speed, and accordingly the 

 question asked is "What is the minimum power required to propel a ship of 

 given displacement (with no explicit restrictions on linear dimensions or shape) 

 at a given speed?" It is recognized that a form which is optimum from this 

 viewpoint may be more expensive to build and hence less attractive as an eco- 

 nomic proposition than some more resistful form. Nevertheless it is useful to 

 know what this purely hydrodynamic optimum is, so that one can judge what pen- 

 alties may reasonably be incurred in departing from it for practical reasons. 



Whilst the hull forms of present-day ships are determined by mainly em- 

 pirical means, it is to be hoped that in the future mathematical theory may be 

 employed as a design tool. This theory is largely concerned with wave resist- 

 ance, so it is of interest to try to establish whether or not present theories of 

 wave resistance, incomplete though they are, are nevertheless adequate for de- 

 sign purposes. Accordingly, the second part of the paper deals with an experi- 

 mental investigation into the adequacy of Inui's (1) approach to the relationship 

 between hull form and wavemaking. In this investigation boundary -layer effects, 

 which sometimes cloud the issue, are kept small. 



To see whether the theoretical approach to design can improve on the con- 

 ventional empirical one, it seems useful to try to beat the target set in the first 

 section of the paper and to design a hull which, for a given displacement and 

 speed, requires less propulsive power than any normal ship. Unless a consid- 

 erably lower power can be achieved in this artificial situation, where no re- 

 strictions are placed on hull shape, it seems unlikely that much improvement 

 can be expected in any real design, where practical limitations will have to be 

 allowed for. The third section of the paper, therefore, deals with an initial NPL 

 attempt at this artificial design problem. This attempt, in a very rough and 

 ready way, pays as much attention to minimizing friction resistance as to wave- 

 making. The experimental results obtained for the designed hull form, though 

 they represent only a fairly small improvement on the best conventional prac- 

 tice, are considered encouraging in view of the crudity of the design methods 



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