Motions of Moored Ships in Six Degrees of Freedom 



DISCUSSION 



Manley Saint-Denis 



University of Hawai 

 Honolulu 3 Hawai, U.S.A. 



I am afraid I must begin by begging the author's forgiveness 

 and the indulgence of the audience for the critical remarks I am about 

 to make on this paper. Perhaps this is the wrong way to start a dis- 

 cussion, but if it is not the right way, it is at least a diplomatic one. 

 However I must confess with some alacrity that my remarks are go- 

 ing to be rather suggestive and tentative and not at all forceful or ca- 

 tegorical. This is due in part, perhaps, to the manifest voids in the 

 paper which have led me to infer, perhaps mistakenly, what might be 

 the full development. Having provided sufficient cushioning for my cri- 

 ticism, it is time that I voice it. I have five specific comments and 

 one general recommendation. 



The first is this : I have been unable to discover anything new 

 in the paper. Lack of originality is not in itself condemnable, of course, 

 if the paper contains other rewards, such as elegance of development 

 or an efficient computer programme, etc. . . But these I find not to be 

 present. 



My second comment is that the paper appears to consist of 

 two parts : an adequate introduction and a short conclusion ; but of the 

 essential development that should be the core of the presentation there 

 is only a hint. It is this parsimony of the essential that I have found 

 to be rather distressing. To rest the paper on reports that, if not pro- 

 prietary, are not generally available militates against an appreciation 

 of it. 



My third comment relates to the author's statement that the 

 solution is valid for a ship moored alongside a dock, a condition that 

 introduces an asymmetric non-linearity in the restoration but this is, 

 in principle at least, a grave insufficiency, for the proximity of the 

 rigid boundary, which is the dock, affects also the hydrodynamic mass, 

 the damping reaction and the acceleration and velocity terms of the 

 excitation, so that all these are non-linear, and the non-linearities 

 are not readily written off as negligible. Indeed, they are quite power- 

 ful. 



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