Breslin, Savitsky, and Tsakonas 



DISCUSSION 



G. J. Goodrich 



National Physical Laboratory 



Teddington, England 



The collection of statistical full scale ship motion data is a long tedious job 

 taking at least a year for a good sample but it would seem that it is now feasible 

 to reduce this to a computer technique. 



Large quantities of recorded sea data are available from weather ships 

 fitted with wave recorders which make regular measurements throughout the 

 year. These data could be fed as input to the computer and the resulting ship 

 motions obtained by the methods suggested by Dr. Breslin. 



The results of the calculations could be sampled statistically in an ex- 

 tremely short time and in this way vast quantities of statistical data could be 

 obtained. 



DISCUSSION 



Samuel M. Y. Lum 

 Bureau of Ships 

 Washington, D.C. 



Aside from minor typographical errors and inadvertent omissions in some 

 of the equations scattered throughout the text, I would like to raise some ques- 

 tions on four issues stimulated by this interesting paper. 



The first involves what appears to be an apparent mathematical oversight. 

 The question concerns the derivation of the wave- induced impulsive response 

 function presented in the appendix. As it presently stands, this will affect some 

 of the other equations and the final result. This oversight will detract from the 

 overall generality and limit the application. I refer in particular to the failure to 

 distinguish between w, the wave frequency, and o^, the system frequency of en- 

 counter. The former is strictly a characteristic of the wave as determined by a 

 wave probe geographically fixed without bringing the craft into the picture. The 

 latter, oi^, is related to the frequency of encounter as seen by a wave probe 

 fixed to a moving reference having the same speed of advance as the craft. This 

 inconsistency or error of omission can readily be detected by going back to the 

 equation of a simple harmonic, two-dimensional progressive wave as seen by a 

 fixed wave probe, 



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