Porthole, port light, sidescuttle

A circular opening in the ship side to provide light and ventilation. A hinged metal cover or deadlight can be clamped over to secure in heavy weather.

Sidescuttles are divided into three types: Type A (Heavy), type B (Medium) and type C (Light). The minimum requirement for type A is that it shall withstand a water pressure head of 24m, 12m for type B and 6m for type C. Sidescuttles may be made for welding or bolting into the ship shell or bulkhead. They may be made with (type A and B) or without inside hinged deadlights (type C).

Scuttle is a synonym of porthole.

As nouns the difference between scuttle and porthole

is that scuttle is a container like an open bucket (usually to hold and carry coal) or scuttle can be a small hatch or opening in a boat also, small opening in a boat or ship for draining water from open deck or scuttle can be a quick pace; a short run while porthole is a circular window set in the hull of a ship.