Lewis 



in this way so there is indeed no reason to use a frequency of encounter spec- 

 trum. For a broad spectrum, containing negative maxima and positive minima, 

 only the number of times may be different but not the percentage of time. This 

 makes it superfluous to make any assumption on the shape of the spectrum. 

 Therefore the interpretation of the results in this manner is more rigorous 

 without being less vigorous. 



DISCUSSION 



L. Vassilopoulos 



Massachusetts Institute of Technology 



Cambridge, Massachusetts 



I cannot help but basically disagree with the philosophy behind this paper as 

 well as the alleged usefulness of the procedures which Professor Lewis pro- 

 poses. The points of the paper, which bear directly to the profession's real 

 needs at present, are unfortunately obscured and are only very briefly treated 

 while the author mainly reiterates his recently proposed technique for interpret- 

 ing results of seakeeping research rather than applying them. 



Despite the fact that we are almost ready to commence an evaluation of the 

 importance of seaworthiness considerations in preliminary ship design, there 

 still exists a definite need for: (a) a scrutiny of the validity and applicability of 

 the basic procedures with which the results of ten years active research have 

 been obtained, and (b) the establishment of a generalized philosophy for applying 

 our knowledge to the actual design process of all ship types. 



With respect to the first item, one notes that members of the profession on 

 occasion fail to adhere to the fundamental notions and implications behind the 

 St. Denis - Pier son approach. It is the writer's opinion that the present paper 

 introduces unnecessary confusion and complication. The author seems to believe 

 that our present procedures rest on such sure principles that we are in a posi- 

 tion to modify and transform these principles. It is with this belief that I dis- 

 agree. 



Professor Lewis has actually recast, without any formalism, the basic 

 Wiener-Kintchine relation of the theory of random processes to suit what he 

 terms the needs of the ship designer. He forcedly transforms the components 

 of the equation 



where 



0- .(cjg) = input function amplitude density spectrum, 



214 



