Leonardo da Vinci proposed a double hull as a way to strengthen a ship and reduce the danger of leaks.
A double hull places an inner hull inside an outer hull, creating a protective space between them. Leonardo’s ship-design studies explored this arrangement as part of a broader effort to improve watercraft construction and safety. The extra layer could make the vessel more resistant to damage than a single outer shell.
The idea should not be confused with a keelson, which is a longitudinal structural member inside a ship, or with a bilge pump, which removes water after it enters. A double hull is a structural arrangement rather than a pumping device or a steering mechanism.
Modern ships use double-hull construction for particular safety purposes, including reducing the chance that damage to an outer shell will immediately open the main cargo or buoyancy space. The modern applications are not identical to Leonardo’s proposal, but the underlying principle—using separated layers for protection—makes the historical connection clear.