PURPOSE: To maintain watertightness of a hatch and also perform its prompt opening/closing by providing a slide fastener mechanism in the medium part of a belt-like sheet material, with its one end fixed to the outer peripheral part of the hatch of hatch coamings and the other end fixed to the upper part of a longitudinal wall of the hatch.

CONSTITUTION: The one end 2a of a strong sheet material 1 shaped like a long belt is fixed to an outer edge of a horizontal material of inflexibility of hatch coamings 20, while the end part 2b of the opposite side is fixed to the upper end end of a longitudinal wall 21S of the hatch. An opening part 3 worked by a slide fastener 4 is formed in the medium part of the sheet material 1. Water-tightness of a gap between the hatch 21 and the hatch coamings 20 is maintained by closing the fastener 4 and opening/closing of the hatch 21 can be promptly performed by means of the slide fastener 4.