Abstract: A trimaran which includes a main hull, starboard hull, and port hull, has positive stability for up to about 130.degree. inclination of the main hull. The starboard and port hulls are pivotally mounted to the main hull, and the mast is mounted to the main hull for pivotal movement about an axis generally parallel to the axes about which the starboard and port hulls are pivotal. Shrouds attach the mast to the starboard and port hulls, and springs may operatively connect the shrouds to the starboard and port hulls, respectively, so that the effective lengths thereof are variable. Springs, and stops, are connected between the main hull and the starboard and port hulls, respectively, to prevent pivotal movement relative to each other unless the wind exceeds a predetermined value.