PURPOSE: To permit a ship to be taken custody of, preventing the ship bottom from making contact with the sea water, by installing, onto the ship-bottom protecting cover for covering the outside part of the ship bottom, a drain pump which is operated through the dipping and heaving of the ship which is caused by the fluctuation of the tide level.

CONSTITUTION: A ship-bottom protecting cover A for covering the ship-bottom of a ship B is formed in an integral form from FRP material etc., and the ship B is covered, with the opened part 2a of said cover A in the opened state. When the opened part 2a is closed by using ropes 3 and clasps 4, a rising wall 2 is positioned on the draft line. When the ship B is dipped and heaved in this state, a small anchor 10 repeats rise and fall on the rope 8 connecting a large anchor 9 to the small anchor 10, and a drain pump 7 operates through a piston 12 and check valves 15 and 16, and the sea water collected between the ship B bottom and the cover A is automatically drained.