Abstract: The invention discloses 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). The boat further includes a superstructure connecting the two demi-hulls transversely; an open space in the form of a tunnel defined between the superstructure and the two demi-hulls; a longitudinal center of gravity position (LCG) for the boat; at least one trim hydrofoil having a chord line (CL) extending between its leading edge and trailing edge and being located in the stern region of the boat and extending at least partially across the tunnel; and an attachment element for attaching all hydrofoils to the demi-hulls substantially along a transverse plane (TP) which is substantially at right angle to the longitudinal vertical center plane of the boat, and having an angle of between 1.degree. and 7.degree.