PURPOSE: To reduce the amount of backwash by predefining the shapes of a shell plate, an inner bottom shell plate, and an outer bottom shell plate from the bow to the stern and the position of each chine from the bow to the stern, forming a hull at the bow into a deep V-shape breaking into three surfaces, and forming the hull at the stern to broaden into a shallow M-shape.

CONSTITUTION: An outer bottom shell plate 4 broadens upwardly and outwardly at the bow and gets twisted downward toward the stern, where the plate 4 is formed to broaden downwardly and outwardly. An inner bottom shell plate 5 extends outwardly and upwardly from a centerline from the bow to the stern and the slope of its transverse section is varied so that it is at a steep angle at the bow and at a gentle angle at the stern. A side shell 3 is formed to broaden outwardly and upwardly at an angle that gets steeper from the bow toward the stern. An upper chine 1 and a lower chine 2 are arranged so that the lower chine 2 is located under an upper chine 1 at the bow, while at the stern the chine 2 is located above the chine 1.