Porthole

A small, usually circular window fitted in a vessel’s side or superstructure.

A porthole admits daylight and, if it is an opening type, ventilation. Marine construction more formally distinguishes side scuttles and windows, but “porthole” is the familiar general term.

Opening portholes have a hinged or removable closure with seals and dogs or another fastening system. Where watertight or weathertight integrity is required, the glass, frame, seal and fastenings must be maintained and the closure secured before conditions make water entry possible.