PURPOSE: To improve the ridigity of a hatch cover and facilitate the handling thereof in a hatch structure wherein an engine casing is expanded to the rear of a cock pit, by forming hatch coamings on inclined surfaces, and making the upper surface of a hatch cover horizontal when the cover is closed.

CONSTITUTION: An engine casing 40 is formed so as to expand in the rear of a cockpit 2. The upper ends of the side walls of the engine casing 40 are formed so that the heights thereof increase toward the sterm side in order to form the inclined surfaces. Moreover, hatch coamings 71W73 are formed on said inclined surfaces. A hatch cover 6 is so formed that the lower end part 60 thereof parallels the hatch coamings 71W73 on said inclined surfaces and the upper surface 61 is approximately horizontal when the hatch cover 6 is closed.