358 F. H. Todd 
value of deadweight to displacement ratio equal to 0.60 for submarine tankers and 0.75 for 
surface tankers, a fair comparison between the two types would be obtained. A comparison 
between surface and submarine tankers is shown in Table 6 for ships having deadweights of 
18,750, 56,250, and 93,750 tons. Using the appropriate deadweight /displacement coeffi- 
cients from Fig. 8, the displacements have been calculated and the ship dimensions, EHPs, 
and DHPs have been taken from the curves obtained as described in the preceding section. 
The results for three of these cases are shown in Figs. 9, 10, and 11, where curves are 
given of DHP to a base of speed in knots for a surface tanker and two submarine tankers 
having respectively circular and elliptical sections. The submarine tanker throughout has a 
prismatic coefficient of 0.60. On the other hand, the block coefficient of the surface tanker 
has been varied to suit the speed/length ratio, being 0.80 at the lower end of the speed 
range and 0.60 at the top end. The figures for the surface tanker do not include any allow- 
ance for the effect of rough weather, and the following remarks therefore apply to smooth 
water conditions for the surface ships, and are favourable to them in this respect. Making 
the comparison in this way, however, enables certain other points to be brought out. 
Looking first at the results for the circular section submarine and the surface tanker, 
we see that at the lowest speeds in question, namely 10 to 15 knots, there is practically no 
difference in the power requirements between these two types of ship. Since there is very 
little wavemaking in the case of the surface ship at these speeds we can infer from this 
that the reduction in form drag for the streamlined submarine as compared with that for the 
surface ship is sufficient to compensate for the increased frictional resistance of the sub- 
marine due to its augmented wetted surface. At higher speeds the circular section submarine 
tanker always requires less power. For vessels having a deadweight of 18,750 tons the dif- 
ference in power is some 5000 on 25,000, and this is about the smallest ship for which a 
nuclear propulsion plant could be designed at present. For the largest ship having a dead- 
weight of 93,750, which is comparable with the largest tankers built today, the power for the 
surface ship at 27 knots is some 190,000 and this is reduced to about 140,000 in the case of 
the circular submarine. It is also worth noting that there is no appreciable difference in 
power for these two designs up to a speed of 23 knots and to get the benefit from the sub- 
marine design one needs to go to higher speeds; however, at 27 knots the figures just quoted 
show that we are faced with a power plant comparable with those of the “Queens,” and this 
of course would involve many problems regarding the housing of nuclear reactors, heat 
exchangers, etc., within reasonably sized containers for fitting in a submarine. When allow- 
ance is made for the effects of weather, the comparison would be much more favourable to 
the submarine, either from the point of view of the greater power and fuel consumption to 
maintain speed on the surface ship or from the loss in speed of the surface ship at the same 
power. Opinions as to the weather allowances necessary on different trade routes vary, but 
the tables and curves given here will enable anyone interested in this problem to make his 
own estimates in these matters for any desired weather conditions. 
Curves are also shown in these three figures for a submarine of the same deadweight 
but having a beam equal to four times the draft. The only factor which has been taken into 
account in making the estimates for these elliptical section ships is the increase in wetted 
surface necessary to obtain the same volume within the elliptical section. Doubtless in 
such a design the displacement would have to be increased to a considerable extent to 
allow for the effect of the different shape of hull upon steel weight, and it is probable that 
the residuary resistance coefficient would also be considerably increased as compared with 
that for the circular section. For both these reasons, therefore, the power curves shown are 
likely to be an underestimate. 
Teasdale has published similar curves for surface and submarine tankers, both nuclear 
propelled, having a deadweight of 45,600 tons including the weight of the reactor [4]. 
