High-Speed Planing Hull for Rough Water 



DISCUSSION 



Manley Saint-Denis 



University of Hawai 

 Honolulu^ U.S.A. 



I am very happy that seakeeping has been treated in this paper 

 as the pre-eminent factor in the design of planing craft, for to the 

 present, seakeeping has been introduced in the design of small craft 

 hardly at all. Indeed it has been ignored except for raising the chine 

 at the bow and narrowing the beam. And then the designers have simp- 

 ly put their trust in God, hoping that he would be kind to them and to 

 the sea -beaten crews that would man in the open sea the craft they had 

 designed. Therefore, I am grateful that something is being done be- 

 cause, waves being independent of the size of the vehicle that ventures 

 over the surface of the sea, I suppose it is not a profound revelation 

 to state that the smaller the craft the more she suffers. For a large 

 vessel, even a heavy sea can be only an inconvenience, but for a small 

 craft even a modest sea can lead to a very miserable experience. 

 Therefore, starting the design of planing craft by considering the sea 

 behaviour as the very first step in the process is the correct way to 

 proceed, and I am glad to see the authors have done just this. 



My second point relates to the authors' conclusion that if you 

 narrow the beam, reduce the trim angle and up the dead-rise, things 

 will be better rather than worse ; and while the exposition of the paper 

 itself gives quite some insight into the sensivity of how impact, sea 

 behaviour and other effects are related to the design features, the 

 designers do not unfortunately go further into the matter. 



I should like to point out that if all the authors wanted to do 

 was to show how to develop a design to fulfil some very rigid specifi- 

 cations, such as the inflexible ones they have stated, the design pro- 

 cess could be shortened considerably. In fact, one could develop a 

 simple computer program that would yield an almost instantaneous 

 answer, for the line of logic is simple and unambiguous in such a case. 

 However, the point I should like to raise is that the specifications are 

 not always quite as rigid as the authors have listed them, that indeed 

 one has to play with them somewhat, giving up somewhat little here to 

 gain somewhat more elsewhere : for example, take the problem of the 

 transverse metacentric height, the metacentric height is reduce by 



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