Submarine Cargo Ships and Tankers 343 
hoped, to stimulate discussion and draw forth new ideas. One of the main advantages of 
nuclear-propelled ships is the saving in space no longer required for bunkers, and the con- 
sequent increase in carrying capacity. The weight of the shielding around the reactors 
cancels out much of the saving in weight by the elimination of fuel, and this would suggest 
that such machinery is most suitable for long-haul voyages. The average dry-cargo ships 
have been developed largely along the requirements of certain trades, and these are not 
likely to alter materially in type. Moreover, the oil fuel is very often carried in the double 
bottom, and such space is not of use for additional cargo. These considerations lead to the 
general conclusion that the ships most suited to nuclear propulsion are those carrying bulk 
cargoes such as ore, grain, and oil. In the case of the latter, with a liquid cargo the ease of 
handling is such that the ships could just as easily be submarines as surface ships, and it 
is this aspect of nuclear propulsion which seems to have caught the public imagination. 
Economic nuclear propulsion in the strictly commercial sense is as yet some time away, 
but if it is eventually to be applied to submarine cargo ships, then there are without doubt 
many difficult problems to solve, and it is certainly not too early to begin research into them. 
if we are to be ready to design and build such ships. 
HYDRODYNAMIC ADVANTAGES OF SUBMARINE SHIPS 
Although this symposium is supposed to deal with the field of naval hydrodynamics, it 
would not be realistic to treat this particular problem purely from that standpoint. There are 
so many practical limitations which would come into the design of a submarine cargo ship or 
tanker that they must be given consideration, as only in this way can we give due weight to 
all the conflicting claims. In this section the question of powering will be considered and 
estimates made for both surface and submarine ships. These will be used later in the paper 
as a basis for discussion when we come to deal with the problems of operating and main- 
taining such craft. 
From the hydrodynamic point of view, the two greatest savings that we can expect by 
going under water are the elimination of the wavemaking resistance and the escape from the 
effects of rough weather. Owing to the good hull form which one can design for a real sub- 
mersible, it is reasonable to expect that the form resistance would also be reduced. 
The wavemaking resistance is a relatively small part of the total resistance for surface 
ships at low speeds, and therefore one would not expect any great savings in power by its 
elimination at low speeds of operation. Indeed, the submarine under such conditions begins 
with a considerable handicap in that the wetted surface will be considerably greater than 
that of the equivalent surface ship and therefore the skin-friction resistance of the sub- 
marine will be considerably higher. Only if this can be offset by a corresponding reduction 
in form resistance will the submarine be able to break even with her surface counterpart. At 
higher speeds the wavemaking resistance of the surface ship begins to increase very rapidly 
(in the order of V°) and to attain these higher speeds a continual fining of the hull is neces- 
sary together with an increase in ship dimensions in order to carry a given amount of dead- 
weight. Eventually we reach a speed at which it is no longer economic to drive the surface 
ship, and it is here that the submarine would show a very real advantage in terms of power. 
We can thus conclude on purely general grounds that the elimination of wavemaking resist- 
ance by using a submarine ship will only begin to give substantial returns when used at 
comparatively high speeds. 
