PURPOSE: To constantly maintain watertightness against deformation due to rolling of a ship's hull, by a method wherein a belt form gasket made of a rubber base material and provided with a nose part having a convex top face is provided in a recessed form socket fitted to a top plate of a hatch edge member, through a shim.

CONSTITUTION: The belt form gasket 1 side-laid D-shaped in cross section is fitted into the recessed form socket 3 fitted to the top plate 13 of the hatch edge member 11. In this case, the shim 2 is used for adjusting the projection quantity of the convex top face of the nose part of the gasket 1. The gasket 1 is formed from a rubber base material, and is engaged to a back-side longitudinal member or transverse member 14 for the hatch cover 12, with the nose part pressed against the member 14. Even when the opening part of the hatch is deformed due to rolling of the ship's hull, the nose part of the gaskset 1 constantly maintains contact with the member 14, thereby maintaining watertightness.