portholes

A porthole is a circular window used on ships and other vessels to admit light and air while preserving the hull’s watertight integrity. It typically consists of a metal frame, a pane of glass, and a shutter or deadlight that can be closed to seal the opening against water.

Construction and design features vary, but most portholes use corrosion-resistant frames—often brass, bronze, or steel—and a sturdy glass pane. The glass may be tempered or laminated for strength, and it is set within a pressure-resistant ring with a gasket to maintain a watertight seal. Many portholes include a movable shutter or deadlight that can be opened for ventilation and closed to protect the interior in rough seas.

History and usage have shaped modern practice. Circular openings were favored on iron and steel-hulled ships because the round shape distributes stress more evenly than rectangular openings. Portholes became common in the 19th century as shipbuilding moved from wood to metal, though earlier ships used various forms of ports. Today, portholes are standard features in crew accommodations and other interior spaces on many vessels, designed to balance light, visibility, and weatherproofing.

Variants and related terms. Similar circular windows appear on submarines and aircraft, and the term porthole is often used generically for circular windows. A deadlight is the cover used to close a porthole, providing a secondary layer of protection when the window is not in use. While operable portholes offer ventilation, they are not typically relied upon as primary means of egress in an emergency.