376 F. H. Todd 
J. A. Teasdale (Furness Shipbuilding Company, Limited, Billingham) 
The largest known military submarine has a displacement of only one-fifth that of the 
smallest vessel considered in this comprehensive paper and so far no fully commercial sub- 
marine has been in service. The author, therefore, is to be congratulated upon his approach 
to the comparison between surface and submarine merchant vessels and the interesting 
presentation of the results of his work. 
In order to properly compare these results with other works on the same subject a little 
more information is required on the data used in the study. Firstly, is the displacement 
referred to in Tables 2, 3, and 6 and Fig. 8 one of surface or submerged condition? Sec- 
ondly, what form drag allowance has been assumed for the submarines? Various sources 
put this allowance as high as 15 percent of the skin friction value. Thirdly, the method of 
determining the deadweight of the submarines seems to be very approximate and perhaps 
misleading. The deadweight/displacement ratio is unlikely to be constant for a range of 
displacement of over 100,000 tons and a range of horsepower of more than 200,000 DHP. 
Since these designs of submarine tanker are intended to be of relatively high speed 
compared with conventional submarines and accurate depth control at low speeds is not so 
important, there should be no necessity for bow diving planes. Even without these it is 
doubtful whether the appendage allowance would be less than 25 percent of the EHP of the 
bare hull. 
The author states, “If we restrict the draught of the submarine to a figure comparable 
with that of the equivalent surface tanker, then we are forced into accepting a submarine 
having elliptical sections.” The writer would venture to suggest that if ever a submarine 
tanker project becomes fact, then the practical design is likely to have a substantial 
parallel body of rectangular section with radiused corners. The ends, of course, would be 
as streamlined as possible. 
R. Brard (Bassin d’Essais des Carénes, Paris) 
Undoubtedly, the question that Dr. Todd has chosen for this Symposium is an interesting 
one. Numerous papers have already been written on this subject, that is, a consequence of 
the promises of atomic propulsion. But the problem of submarines, cargo ships, and tankers 
is quite different from that of navy ships and there is no evidence that the excellent navy 
solution is excellent for merchant marines. Dr. Todd made a very acute analysis of the 
various parts of the problem. He examined them not only from a hydrodynamical point of 
view, but also from others that are to be considered, and particularly those of the operating 
problems, terminal problems, and economical problems. I think that the values of the main 
parameters on which Dr. Todd grounds his analysis, should not give rise to discussion, but 
in a final synthesis, the weights of each aspect could be somewhat subjective. The con- 
clusion of Dr. Todd seems, however, prudent and full of sense. Many studies are necessary 
before submarine cargo ships and tankers become practical, but those concerned with this 
question will find in Dr. Todd’s reflections many very useful materials. 
F. H. Todd 
I am grateful to Admiral Brard for his remarks, and agree completely with his opinion 
that military and commercial submarines are two quite different propositions. It was my 
