366 F. H. Todd 
penalty on weight in going to the elliptical section. However, in a cargo-carrying submarine 
or a tanker in which the whole hull was built to resist pressure, then there would be a very 
substantial penalty in weight through such a change in shape. The comparison between the 
submarine and the surface ship is therefore seen to be more unfavourable to the submarine 
' when we consider a hull with elliptical sections. 
The outcome of this whole discussion points to the fact that from a commercial point of 
view there is little attraction in submarine cargo ships or tankers so long as we restrict our 
thoughts to speeds within the limits for which economic surface vessels can be designed. 
However, if we wish to go beyond these speeds, then the submarine would be the only 
answer for the carriage of bulk cargoes. For lighter specialised cargoes, it may well be that 
the answer is to go the other way and use hydrofoil craft. If submarine ships were justified 
by a sufficient demand for the transport of bulk cargoes at such high speeds, the figures that 
have been given for the powers required, even when we are not compelled to make provision 
for surface wavemaking and rough weather, still mount rapidly and very soon attain astro- 
nomical proportions. In Table 3 a line has been drawn showing where the power required 
exceeds 200,000 DHP, which means a propelling installation of the same order of magnitude 
as that of the QUEEN ELIZABETH, and of course to house any such nuclear plant in a sub- 
marine would be quite a task. The containing vessel for the 20,000-shaft-horsepower nuclear 
plant for the American cargo ship SAVANNAH is 50 feet long and 35 feet in diameter, and 
one can imagine that with 200,000 horsepower together with the space required for perma- 
nent ballast, trimming tanks, buoyancy tanks, living quarters, and so on, the deadweight/ 
displacement ratio would be rather small. 
From time to time it has been suggested that a smaller tanker of the nuclear propelled 
submarine type might be competitive with a much larger surface tanker. Such a comparison 
has been made by Teasdale [4] between a 47,000-ton-deadweight surface tanker and a 
26 ,000-ton-deadweight submarine tanker of circular cross section and having dimensions 
which do not exceed those of the surface ship. He estimated that if the submarine were 
travelling at a high enough speed to deliver the same quantity of oil per year as the surface 
tanker, the fuel consumption would be about four times as great. From his analysis he 
doubted whether the capital cost of the submarine would be sufficiently less than that of 
the surface ship to offset such a penalty. 
TERMINAL PROBLEMS 
The draft of water in many ports and harbours today does not exceed 35 feet and in 
very few does it exceed 50 feet. This would impose many problems on the building and sub- 
sequent dry-docking of submarines of the size we have been discussing. The draft problem 
could be overcome by going to an elliptical section shape for the hull, but this would give a 
submarine of excessive beam for most dry docks and would also bring in the other problems 
which we have mentioned in the previous section. For the ordinary routine loading and 
unloading processes, it would be necessary to build offshore loading terminals or use feeder 
services to bring the oil in to the refineries. This would mean that the ship might be sub- 
ject to rough weather and therefore would have to be designed with normal longitudinal 
strength and not be able to have a light scantling outer structure. Another point of some 
interest for such large ships approaching the shore is the fact that once the depth of water 
was reduced much below 600 feet they would have to surface and do the last part of their 
journey as surface ships. To achieve the high efficiency of underwater propulsion which 
has been the aim of all these designs it is necessary to go to a streamlined body of revolu- 
tion with the very minimum of appendages. However, when such a vessel has to come to 
