Seakeeptng Constderattons in a Total Destgn Methodology 
these factors off against the propeller efficiency. 
So it would seem that improper assumptions have been made in 
this paper regarding propeller selection, 
Even in the case of the merchant ship design it is hard to con- 
ceive of a ship being power limited in a seaway prior to arriving at 
the voluntary limitation point. Here in propeller design we again con- 
sider stress and vibration characteristics for full power, but design 
for maximum efficiency at 80 percent power. While 80 percent is an 
arbitrary number arrived at through experience, it is a design point 
of some significance to the ship owner. It represents a real value 
around which full scale propeller performance can be evaluated and 
indicates whether the propeller is on or off design. This performance 
determines payment or financial penalty for the designer. It appears 
that the proposed procedure may tend to shroud this well defined de- 
sign point in statistical vagueness. 
REPLY TO DISCUSSION 
Chryssostomos Chryssostomidis 
Massachusetts Instttute of Technology 
Cambridge Massachusetts, U.S.A. 
Answering Dr. Saint-Denis first. The thesis of my paper is 
that in the first iteration of the proposed methodology, once the user 
decided to adopt a cruiser stern monohull as the solution to his pro- 
blem, Series 60 ships form as good a basis as any other standard 
series or for that matter as any other realistic point designs to pro- 
vide the information needed to make the decisions called for in the 
first iteration of the proposed methodology. The small variations bet- 
ween the final design and whatever standard form was used do not in- 
fluence the outcome of the first iteration and their effect need only be 
considered as it is suggested in the paper, in the subsequent itera- 
tions of the proposed design methodology. 
Roll was not included in the present study, as it was stated in 
the paper, not because it was considered unimportant but because the 
state of the art is such that does not permit theoretical prediction of 
roll with any reliability and therefore a creation of a theoretical de- 
rived standard series for roll was considered unwise. 
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