Hatch is the term used for both the passage (hatchway) and the cover to it.

It is called the hatchway.

If it is a round opening, it is called a scuttle. If it is a square opening it is called a hatch. Depending on the vessel and the location they can be "dogged" open.

The scuttle is a hatchway between decks of a ship - when you scuttle a ship you deliberately allow it to fill with water and sink by opening these hatches (or by making hatches yourself with an axe).

Truman died aboard ship from falling into a hatchway. Death listed in Fernandia Beach FL., 24 November 1880. He had lived in Courtland New York.

The CSS David was a different type of warship. It was semi-submersible. The David would submerge until its deck was hidden. Only the hatchway and smokestack was above the waterline. The idea behind this weapon was to ram a torpedo at a Union ship then back away to avoid the torpedo explosion.