10 O. H. Oakley 
used mechanical “feelers” to sense the waves ahead of the boat, and which, through link- 
ages, adjusted the angles of attack of the forward foils. This craft was also successfully 
operated using a resistance height sensing device on the forward struts and an electronic 
“hydropilot ” The most successful of these craft was “Sea Legs,” by Gibbs and Cox, 
shown in Fig. 10. “Sea Legs” has submerged foils in a canard arrangement and a sonic 
height sensing system which actuates the control surfaces through an autopilot and hydrau- 
lic servos. 
Fig. 10. A test hydrofoil craft, the Gibbs and Cox “Sea Legs” 
Based on the successful performance of “Sea Legs” the submerged foils-autopilot sys- 
tem, was used for the antisubmarine hydrofoil craft “PC(H).” Fig. 11 shows an artist’ s 
concept of PC(H), for the construction of which a contract has recently been awarded to 
the Boeing Aircraft Co. 
These craft are all of the subcavitating type. The maximum speed for subcavitating 
craft for all practical purposes is limited by cavitation to about 55 knots in calm water. It 
should be noted however that the XCH-4 attained a speed of about 65 knots. This craft, 
however, was overpowered and lightly loaded, so that any added drag due to cavitation was 
probably not limiting. In rough water, wave orbital velocities induce variations inthe angle 
