8 O. H. Oakley 
compete with a destroyer hull form of equal displacement, the near surface craft must travel 
below a depth of about one and a half diameters to the axis. This implies a strut length 
somewhat greater than one hull diameter plus additional length in order to project some dis- 
tance above the free surface to allow for waves and depth control variations. Such a strut 
must carry at least a periscope or closed circuit TV camera unit, communications and radar 
antenna and a snorkel head valve. The size of the air passages appears to govern the size 
of the strut. For a 20,000 shaft horsepower installation, some 80 square feet of intake, 
exhaust and ventilation duct is needed. This results in a strut with a chord of some 26 feet 
and a thickness of 6-1/2 feet, altogether not a small structure. The resistance of this strut 
would degrade the speed performance and affect the stability and control. 
Just as the ram wing needs controls like an airplane, the near surface craft needs con- 
trols like a submarine. In fact, the controls have to be more effective to counter the effects 
of surface waves. Also, the structure would have to be sufficiently strong to withstand 
accidental deeper submergence. 
Hydrofoil Craft 
Hydrofoil craft promise primarily high speeds. It appears likely that speeds in excess 
of 100 knots are possible. In addition, motions in a seaway should be considerably less 
than buoyant craft of the same displacement. These craft can maintain high speed in sea 
conditions considerably more severe than would compel a displacement craft to slow down. 
The United States Navy has maintained a hydrofoil program since shortly after World 
War IJ. Out of this has come considerable research and development, and a number of test 
craft embodying some promising principles. Four of these are shown in Figs. 7, 8, 9 and 10. 
Fig. 7. A test hydrofoil craft, the Baker “High-Pockets” 
