Seakeepitng Constderattons tn a Total Destgn Methodology 
DISCUSSION 
Manley Saint-Denis 
Untverstty of Hawai 
Honolulu, U.S.A. 
I should like to suggest that the paper does not live up to its 
title. The problem of seakeeping is both one of tremendous scope and 
the preeminent hydrodynamic one facing the ship designer, but the 
reduction of such a problem to the determination of the speed lost in 
head seas of the Pierson-Moskowitz type, having a height of roughly 
8 ft., is, I think, something too brutal. To try to predict the seakeep- 
ing characteristics of the ship in such a manner is like trying to pre- 
dict the behaviour of all ladies (and some non-ladies) by that of one's 
own wife. I should like to think that one might be in for some surprises. 
To develop the proper perspective note that for over a century 
the ship designer has equated seakeeping to transverse metrocentric 
height. It is obvious that one parameter is insufficient to cover all 
the sins and virtues of a ship, but one cannot overlook the experience 
of past years, which indicates that of all the aspects that of roll is by 
far the most important. The greatest motion is that of roll, and the 
greatest danger comes in roll. But the only time the author mentions 
the work roll is when he speaks of recommendations on viscous roll 
damping research, and even that recommendation is unsupported by 
anything in the text. This I find to be a disturbing omission. 
Of the three iterations, only one is developed, and that one 
partially, and the other two are only hinted at. The first iteration is 
simply a recommendation that the seakeeping behaviour of a ship is 
assessed in some approximate manner by how a series 60 ship behaves 
when fitted with a Wageningen B.4.55. propeller. The series 60 was 
designed to find out how resistance varied with pertinent parameters. 
But the tests undertaken certainly did not cover adequately the para- 
meters of form that are important for seakeeping. In fact, Dr. Todd 
and his collaborators did not even think about seakeeping in those days. 
But that I mean to say that series 60 good as itis for estimating the 
resistance of ships of normal form, it is not necessarily relevant to 
determining the seakeeping characteristics of any ship that a designer 
might have in mind ; and indeed the relevance of series 60 is nota 
point to be assumed but a point to be approved, if anything, and I do 
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