Catamaran with hydrofoils

A catamaran type boat having two similar boat demi-hulls which are spaced apart and which are substantially parallel, each demi-hull having a base line (BL) extending longitudinally tangentially to the lowest boundary of the surface of the demi-hull at the midship ordinate, the boat further including:

• (a) a superstructure connecting the two demi-hulls transversely;
• (b) an open space in the form of a tunnel defined between the superstructure and the two demi-hulls;
• (c) a longitudinal centre of gravity position (LCG) for the boat;
• (d) at least one main hydrofoil, having a chord line (CL) extending between its leading edge and trailing edge and extending at least partially across the tunnel, and being adapted to be under water;
• said main hydrofoil being located substantially in the vicinity of the LCG;
• (e) at least one trim hydrofoil having a chord line (CL) extending between its leading edge and trailing edge, said trim hydrofoil being located in the stern region of the boat and extending at least partially across the tunnel;
• the projected area of the main hydrofoil being 3 to 5 times larger than the combined projected area of all trim hydrofoils;
• and
• (f) attachment means for attaching all hydrofoils to the demi-hulls substantially along a transverse plane (TP), which is substantially at right angles to the longitudinal vertical centre plane at the boat, and having an angle between 1.degree. and 7.degree. to the base line (BL) of the demi-hulls at the main foil, and with the hydrofoil chord lines (CL) being at an angle of between 0.degree. and 6.degree. to the transverse plane (TP), the attachment means being adapted to locate the hydrofoils such that their combined resultant lift-force at speed is adapted to act lengthwise through a point in the vicinity of the longitudinal centre of gravity (LCG) and wherein said attachment means locates each hydrofoil such that at highest speed the average water height is 20% to 50% of the chord length.