A boat hull providing substantially enhanced stability, safety and comfort over conventional boat hulls in common use, incorporating at least one relatively narrow, more-or-less vertical slot (23) running longitudinally and/or laterally through the hull of the boat and positioned so that the slot(s) (23) intersects a major portion of the depth of the water displaced by the boat hull. The slot(s) (23) may be fully or partially closed at any of its fore-end (31) or aft-end (33) or bottom-edge (25).