Breslin, Savitsky, and Tsakonas 



REPLY TO THE DISCUSSION 



p. Breslin, D. Savitsky, and S. Tsakonas 

 Stevens Institute of Technology 

 Hoboken, New Jersey 



It is a rather difficult task to try to answer all the discussers of our paper 

 due to the variety of aspects tackled by the discussers and due to the extent to 

 which some of them went. Some of the facts brought up by Dr. Yamanouchi and 

 Dr. Pierson should be considered as complete and independent studies and de- 

 serve better classification than being characterized as discussions.* 



The estimation of impulse response function by statistical methods as sug- 

 gested by Dr. Yamanouchi is interesting and useful since it incorporates better 

 the statistical properties of the medium. But the evaluation of the impulse func- 

 tion through a large number of algebraic equations makes the method somehow 

 cumbersome and of questionable stability. His comments on the effect of non- 

 linear damping on the calculation are very interesting but not directly related to 

 the linear problem which is under consideration. 



Dr. Pierson's remarks on the subjects (a) ship in short-crested waves and 

 (b) coherency and resolvability of spectral and cross- spectral shapes and (c) the 

 solution of specific problems which are nonlinear, are interesting and applicable 

 to the problem of ship motion in short-crested waves, where the nonlinear char- 

 acteristics are dominant. 



As for Mr. Lum's remark about some "mathematical oversight" by the au- 

 thors, we would like to emphasize the fact that the primary objective of this 

 present paper is to demonstrate the method of evaluating the impulse response 

 function of a marine craft running in arbitrary irregular long- crested waves, 

 and bring up the most pertinent characteristic of the approach. Thus an ideal- 

 ized situation was selected such as to exhibit the main feature of the approach. 

 Equations (11) and (12) do not imply the corresponding system to be one of 

 "lumped parameters" since the coefficients are frequency dependent. We should 

 further keep in mind that this study is based on a linearized version of the cou- 

 pling ship motion in heave and pitch and the results are applicable only for long- 

 crested waves. His burning desire to reach the stage of issuing criteria and 

 formulae useful for the design of a ship for seaworthiness and minimum motion 

 can only be achieved after a rigorous and more realistic study of the hydro- 

 dynamic aspects of the problem. The fulfillment of this long range objective 

 should wait until this part of the problem is clarified and, in the meantime, the 

 fragmentary information should be properly utilized. 



*See discussions by Pierson and Yamanouchi on the paper by Ogilvie and discus- 

 sion by Tick on the paper by Cunnmins and Snnith. 



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