14 O. H. Oakley 
Foil smoothness is, of course, vital to good performance. Present tests indicate that 
paint (both anticorrosive and antifouling) is likely to peel off at high speeds. One promis- 
ing approach is the Cox System of cathodic protection. In this method, high current densi- 
ties are applied when the boat is motionless in the water. This plates out a combination of 
magnesium hydroxide and calcium carbonate on the foils. The idea is that the fouling will 
attach to this rather soft coating, and slough off at reasonably low forward speeds. A mini- 
mum value of current density is applied at all times to eliminate corrosion. 
The Navy’s present activity in the hydrofoil area includes an extensive research and 
development program directed toward a large experimental subcavitating hydrofoil ship of 
about 300 tons displacement and a small superventilating hydrofoil boat (about 15 tons) to 
be in operation by 1963. 
Shark Form 
If we do not try quite so hard to avoid the free surface, and if we acknowledge that 
certain armament and surveillance activities require topside space, then it is not a long 
step from the concept of near surface craft to the shark form of Fig. 1. In effect, this is 
simply a near surface craft with a relatively large strut piercing the surface. The shape and 
location of this large strut should be such as to cancel as much of the main hull’s wave 
resistance as possible and reduce the exciting forces and moments due to sea action. Thus, 
the promises of the shark form are high speeds and small motions. 
This concept was explored to some extent by the Germans during World War II, andthis 
resulted in the Englemann craft. This form should have favorable motion characteristics, 
especially in head seas, because of the long natural periods of pitch and heave, which 
result from the short, fine waterline. 
Fig. 14 shows a comparison of the shark form and a destroyer type hull form. At the 
lower Froude numbers, the shark form is quite resistful; however, at high speeds, the shark 
form is better than the destroyer form. 
There are a number of problems to be resolved before the promises of this form can be 
realized. 
As shown in the case of the near surface craft, the submerged hull must be located 
well below the free surface in order to minimize wave-making resistance and the exciting 
forces of the sea. In common also with the near surface craft, the shark form requires 
power plants of less specific volume than currently available in order to attain the speed- 
power advantages shown in Fig. 14. 
The amount of topside weight which can be carried is limited by the low transverse 
stability. With very little waterplane, stability must be attained by keeping the center of 
gravity below the center of buoyancy. This is not easy in a form such as this, in the face 
of the demand for topside locations for equipment. 
The shark form has, in common with the ground-effect craft, a problem of running trim 
in calm water. Fig. 15 compares observed trim tendencies at zero angle of attack with those 
calculated from Pond’s theory for Rankine ovoids. This comparison is, of course, not 
strictly valid because of the difference in submerged hull shape and the fact that the theory 
does not take into account the topside shape of the shark form. Even so, the trends do 
