Foil arrangement for a planning craft

Claim 1

In a catamaran of the type having two spaced-apart, substantially parallel demihulls joined by a deck structure above the waterline forming a tunnel, said demihulls having a waterplate at the design speed which forms the planing angle with the keel lines of the demihulls, the improvement comprising: a mainfoil and a trimfoil disposed at an angle of attack withing said tunnel below the waterline and respectively positioned a relatively short distance aft, and a relatively longer distance fore of the longitudinal center of gravity of the catamaran, said main and trimfoils effecting dynamic lift forces at the design speed having a resultant acting closely adjacent to the longitudinal center of gravity, said trimfoil disposed adjacent to the keel of the demihulls and vertically below said mainfoil such that when the catamaran moves at the design speed, said foils have approximately equal drafts.