PURPOSE: To restrain increases of the frictional resistance of a hull and the wake coefficient in the surface of a propeller caused by stains by providing a coating of anti-staining and anticorrosive material on the seawater side of the outer shell containing the stern part equivalent to about one-fourth of the whole length of the hull.

CONSTITUTION: A coating of anti-staining and anticorrosive material or a painted layer of the above-said character is provided on the outer shell containing the stern part equivalent to about one-fourth of the whole length of a hull for making this area a smooth face part 3. This construction permits to restrain increases of the frictional resistance of the hull and the wake coefficient in the surface of a propeller 4 caused by stains. As another example of practice, a smooth face part 3a made on the outer shell containing the stern part equivalent to the one-fourth of the whole length of the hull and the bottom side equivalent to about a half of the load waterline 6 can be considered. In this illustration, 2 indicates a rough face part of the hull, and 5 indicates a rudder.