A hatch or door system secures and seals an opening in a surrounding structure, such as a horizontal or vertical surface of a marine vessel. A panel having at least two straight edges is rotatably mountable to the surrounding surface. An operating mechanism is mounted on the surrounding structure, rather than on the panel, to retain the panel in the closed position. The operating mechanism includes dogging members configured to apply a force along at least a portion extending continuously along each of the two straight edges when in a panel-securing position. A gasketing mechanism is included to seal the panel in the closed position.