Abstract: The hatch cover is secured and locked in place by a spider which is rotatable into locking position against the underside of a deck ring which receives the cover plate. The spider is clamped by a center bolt passing through the cover and the spider. Means are provided on opposite ends of the center bolt for rotating it from either the outside or inside of the cover. The cover is adapted to stow a removable wrench for this purpose recessed in the outside of the cover. A peripheral seal on the cover plate maintains a water tight and air tight joint when the cover is clamped and locked in place while allowing metal to metal contact between the cover and supporting ring when necessary.