Abstract: A boat comprises a central hull member (10), such member having no flat surfaces below the waterline such as could support the boat in a planing mode, the ratio of the length of such member to its beam being no less than 5 to 1, and a respective auxiliary member (12, 14) connected to each side of the central hull member and extending therealong, the auxiliary members extending to a lesser depth than the central hull member, the ratio of the beam of the boat to the beam of the central hull member being no more than two.