Leonardo da Vinci proposed a double hull as a shipbuilding feature intended to reduce the danger of a breached outer hull.
A double-hull arrangement places an additional layer inside the exterior hull, creating a space between the two surfaces. If the outer layer were damaged, the inner layer could help keep water from entering the main interior of the vessel. The concept reflects Leonardo’s wider interest in buoyancy, water resistance, and naval engineering.
This idea should not be confused with a double-ended ship or a strengthened keel. Its defining feature is two hull layers separated by an intervening space. Modern ships use double hulls in several contexts, including oil tankers, although modern construction methods and safety rules differ greatly from Renaissance proposals.
Leonardo’s ship studies were largely designs and investigations rather than a documented program of full-scale construction. His sketches nevertheless anticipated engineering principles that later became important in marine safety.