porthole

A porthole is a circular window installed in a ship’s hull, deckhouse, or other marine structure. It combines light and ventilation with a requirement for watertight integrity and resistance to sea pressure. The term porthole derives from port, the side of a ship, and hole, reflecting its function as a controlled opening in the vessel’s side.

Construction and design: A porthole typically has a robust metal frame—commonly brass, bronze, steel, or aluminum—surrounding one or more panes of glass or clear plastic. The glazing is usually tempered or laminated for impact resistance. The opening is sealed with a gasket, and a deadlight or cover can be closed to keep out water. Some designs use multiple layers to improve insulation and safety.

History and use: Portholes became widespread on oceangoing vessels in the 19th century as hulls were built to withstand greater pressures and the need for daylight and ventilation grew. They replaced or supplemented open ports and gun ports in many ships. Modern portholes are designed to meet maritime safety standards and are built to withstand repeated pressure, waves, and exposure to salt air.

Variants and scope: Although most strongly associated with ships, the term is also used for round windows on submarines and some aircraft or architectural applications. In practice, portholes are valued for providing light and visibility while preserving the hull’s integrity and watertightness.