PURPOSE: To reduce wave drag by forming a pipe trunk in the vicinity of the bottom of a ship hull from the stem to the stern thereof, and by sucking in waves to be thrusted aside by the stem through an opening at front end with the use of a drainage such as, for example, a pump arranged in the stern, and as well by jetting the water through a drain opening at the rear end.

CONSTITUTION: A pipe trank 2 having a predetermined diameter shape is laid through a ship hull from the stem to the stern thereof, and drainages 5 such as, for example, a screw, a pump or a water jet are diposed at the intermediate part and the rear end part of the pipe trank 2. The ship 1 sails on the sea and the drainage 5 such as a screw is driven by a suitable drive source, and therefore, waved water impinging against the stem is sucked in the pipe trunk 2 through the front end 3 thereof, and is jetted or pushed rearward, thereby wave drag is aimed at being reduced during the sail of the ship.