Submarine Cargo Ships and Tankers 355 
effects of this, estimates have also been made for submarines having elliptical cross sec- 
tions in which the maximum beam was four times the maximum draft. For a circular-section 
submarine the draft could also be decreased by an increase in the length/diameter ratio, but 
this would involve a progressively greater increase in drag and also a considerable penalty 
in the form of extra hull weight. 
In order to convert the EHP values for the submarines to DHP, the same assumption as 
for surface ships has been made regarding the range of powers for one-, two-, and four-screw 
arrangements. The QPC has been assumed to be 0.80 for the single-screw designs and 0.67 
for the twin- and quadruple-screw. The propulsive efficiency for the single-screw arrange- 
ment has been taken somewhat higher than that for the corresponding surface ship because 
of the better wake conditions attained behind the body of revolution form. For appendage 
resistance, 20 percent has been allowed for the conning tower, rudders, stern and bow diving 
planes, flooding holes, and similar items not present on a surface ship, a further 10 percent 
for bossings or shaft brackets on the twin-screw ships, and 20 percent for the quadruple- 
screw ships. These figures give total allowances of 20 percent, 30 percent, and 40 percent 
for the one-, two-, and four-screw arrangements respectively. 
The above figures for the submarine are based on the assumption that it is sufficiently 
deeply immersed below the surface that there is no residual wavemaking. This means as a 
rough guide that it is immersed to a depth of at least half its length or some 4 or 5 diam- 
eters. The effects of depth of submersion have been investigated by model experiments in 
the Saunders-Roe tank. Models representing an 80,000-ton-displacement submarine were 
run at various depths below the surface from 100 to 300 feet and over a corresponding ship 
speed range of 20 to 50 knots [3]. The values of the resistance for a length/diameter ratio 
of 7 are shown in Table 5 and plotted in Fig. 7. There is certainly some depth effect still 
in evidence at the deepest depth of submersion, namely 300 feet, as is shown by the in- 
crease in resistance with speed at that depth. As the depth is decreased it is seen that the 
increase in resistance for the lower speeds does not increase very rapidly until the depth 
reaches something approaching 100 feet. For the higher speeds, however, the increase is 
much more rapid and for 50 knots, for example, the increase between 300- and 100-foot sub- 
mersion is no less than 200 percent. It is therefore evident that if we are to obtain the full 
benefit from the elimination of wavemaking resistance any large submarine of this type must 
Table 5 
Effect of Depth of Submersion on Resistance 
for a Submarine of 80,000-Ton Displacement, L/D = 7, and Maximum 
Section 40 percent L from Nose (from Ref. 3) 
Speed (knots) 
Saicesteheta cle DRL MM AS wl 50k, | 
Values* of R/V? x 10-4 
(ft) 
*R = resistance in pounds; V = speed in knots. 
