PURPOSE: To minimize the degradation of a deck rigidity by reducing the opening area of an opening formed flatly on a deck plane.

CONSTITUTION: A deck 2 is comprising the stem bulge 8 forming the top stem storage, the deck plane 9, the engine hatch bulge 10, and the bridge bottom 11 solidly. The opening 17 is provided to join the top engine hatch bulge 10 with the front thereof (rising plane), the engine being inclined to move within the hull to mount on a specified position to allow to connect and seal the opening 17 with a plate 18 which is formed separately. This permits to provide the opening for the front to connect and seal with the plate material for minimizing the degradation of rigidity of the deck 2.