SUBMARINE CARGO SHIPS AND TANKERS 
F. H. Todd 
National Physical Laboratory 
INTRODUCTION 
The naval architect has always had to battle with the twin elements of wind and water, 
and these have provided very powerful barriers to any great increase in the speed of ships. 
Because a ship is floating at the boundary between two elements of very different densities, 
it creates waves on the surface as it moves and any increase beyond a certain speed leads 
to an excessive increase in the wavemaking resistance and consequently to an uneconomic 
rise in costs of construction and operation. This situation may be thought of in some 
respects as being analogous to the “sonic barrier” in aircraft design. Much research has 
been carried out into the reduction of wavemaking resistance, both by experiment and theory, 
and this has led to the adoption of very fine waterlines forward, U shaped sections and bulb- 
ous bows, which has enabled the speed of surface ships to be raised appreciably in the 
course of the years. 
The effect of the wind is not only to increase the drag of the ship by its direct effect, 
but by creating rough seas or storm conditions forces the ship to slow down to avoid the 
excessive pitching and heaving motions and the damage to the structure which would even- 
tually ensue. Such slowing down means loss of time or subsequent expenditure of extra 
power to make up schedules, since in general no owner wishes to do other than make full 
use of a very expensive investment. Again, research has done much to help the naval 
architect combat such conditions. The adoption of fine entrances, high freeboards, and good 
flare above water have, for example, enabled designers to improve the seagoing qualities of 
trawlers almost beyond recognition, while the perfecting of antirolling fins has reduced this 
motion to almost negligible amount in those ships fitted with them. There remains the prob- 
lem of reducing pitching by similar means, and the bulbous bow does present some advan- 
tages in this way also. 
The naval architect may well have envied his aeronautical colleague who, faced with 
similar weather problems, has taken the modern aircraft to very high altitudes where atmos- 
pheric conditions are calmand stable. He has long been aware of the possibilities of lifting 
a ship above the water surface on foils to reduce its own wavemaking and avoid the surface 
wind-generated waves, and of the advantages of taking a ship below the surface to escape 
both rough weather and wavemaking resistance. 
The perfecting of the internal combustion engine, which enabled the aeronautical 
engineer to achieve his desires by giving him a source of power having a high power/weight 
ratio and a relatively high efficiency, also allowed the naval designer to build hydrofoil 
boats which can attain the same speed as a high-speed conventional motor boat for about 
half the power. These are not new in conception, for the first such hydrofoil craft “flew” in 
Italy as long ago as 1906, attaining a speed of some 38 knots [1]. Of recent years the inter- 
est in hydrofoil boats has greatly increased, many new foil configurations have been evolved, 
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