A stabilised hull of a monohull keeled sail/power-sail boat whereby the hull total width not exceeding 50% of its length, which in its lower part - is embodied with a longitudinally arranged, symmetrical in relation to the boat centerline and commensurate to its length, vertically oriented narrow section of low wave/hydrodynamic resistance, with a water displacement segment, including a keel with a heavy bulb, - therein, the length-to-width ratio of that segment waterline is at least 7x times, with the segment water displacement corresponding to the fully loaded weight of the boat, - therein, the narrow section is embodied with wave piercing lines, a high wave piercing stem, streamlined back lines, and a streamlined spatial widening in the upper front part thereof, - it also includes two longitudinally oriented, symmetrical in relation to the boat centerline, sponsons (6, 7), located above the waterline along the bottom surface of the hull at maximum hull width; in relation to the hull length, the sponsons (6, 7) may be located either closer to the stern, the middle or to the bow part of the hull, - the sponsons (6, 7) and the water displacement segment being separated from one another by laterally extending hull portions which are provided over the entire length of said sponsons (6, 7); wherein, when the boat is at rest in the water, said water displacement segment projects beneath the waterline and possesses sufficient width to carry the fully loaded weight of the boat whilst said sponsons (6, 7) and said laterally extending hull portions remain above said waterline, characterized in that the sponson length-to-width ratio is at least 7x times, with its own volume sufficient for parrying heeling under sail at submersion of the leeward sponson, but not sufficient for keeping the boat afloat, the sponsons (6, 7) have a streamlined, spindle-shaped form with wave piercing front, streamlined rear and planing middle lines, and in that said sponsons (6, 7), water displacement segment and said hull portions forming above the waterline and either side of said water displacement segment two tunnel cavities said tunnel cavities being of a size sufficient for dissipating the energy of the wave broken by the stem and the sponsons (6, 7). whereby the hull total width not exceeding 50% of its length, which in its lower part - is embodied with a longitudinally arranged, symmetrical in relation to the boat centerline and commensurate to its length, vertically oriented narrow section of low wave/hydrodynamic resistance, with a water displacement segment, including a keel with a heavy bulb, - therein, the length-to-width ratio of that segment waterline is at least 7x times, with the segment water displacement corresponding to the fully loaded weight of the boat, - therein, the narrow section is embodied with wave piercing lines, a high wave piercing stem, streamlined back lines, and a streamlined spatial widening in the upper front part thereof, - it also includes two longitudinally oriented, symmetrical in relation to the boat centerline, sponsons (6, 7), located above the waterline along the bottom surface of the hull at maximum hull width; in relation to the hull length, the sponsons (6, 7) may be located either closer to the stern, the middle or to the bow part of the hull, - the sponsons (6, 7) and the water displacement segment being separated from one another by laterally extending hull portions which are provided over the entire length of said sponsons (6, 7); - is embodied with a longitudinally arranged, symmetrical in relation to the boat centerline and commensurate to its length, vertically oriented narrow section of low wave/hydrodynamic resistance, - therein, the length-to-width ratio of that segment waterline is at least 7x times, with the segment water displacement corresponding to the fully loaded weight of the boat, - therein, the narrow section is embodied with wave piercing lines, a high wave piercing stem, streamlined back lines, and a streamlined spatial widening in the upper front part thereof, - it also includes two longitudinally oriented, symmetrical in relation to the boat centerline, sponsons (6, 7), located above the waterline along the bottom surface of the hull at maximum hull width; in relation to the hull length, the sponsons (6, 7) may be located either closer to the stern, the middle or to the bow part of the hull, - the sponsons (6, 7) and the water displacement segment being separated from one another by laterally extending hull portions which are provided over the entire length of said sponsons (6, 7); wherein, when the boat is at rest in the water, said water displacement segment projects beneath the waterline and possesses sufficient width to carry the fully loaded weight of the boat whilst said sponsons (6, 7) and said laterally extending hull portions remain above said waterline, characterized in that the sponson length-to-width ratio is at least 7x times, with its own volume sufficient for parrying heeling under sail at submersion of the leeward sponson, but not sufficient for keeping the boat afloat, the sponsons (6, 7) have a streamlined, spindle-shaped form with wave piercing front, streamlined rear and planing middle lines, and in that said sponsons (6, 7), water displacement segment and said hull portions forming above the waterline and either side of said water displacement segment two tunnel cavities said tunnel cavities being of a size sufficient for dissipating the energy of the wave broken by the stem and the sponsons (6, 7).