Abstract: In this paper, a semi-planing wave-piercing boat combining a hybrid tumblehome bow and a semi-planing hull, which has the features of both a wave-piercing boat and a semi-planing boat, is proposed to achieve the abilities of cutting through waves and decent speed. The semi-planing wave-piercing boat's freeboard has knuckles and is designed as anti-submergence. The freeboard could control submergence faced by a tumblehome bow, producing positive lift and extra reserve buoyancy, and improves the roll. The longitudinal angle of the anti-submergence freeboard is analyzed, and the boat's sailing characters in calm water with a chosen angle are calculated in a numerical way with dynamic mesh. The results show that anti-submergence freeboard works better with small longitudinal angles, and the boat has smaller drag and better hull gesture at high speed compared to a high-speed displacement wave-piercing boat.