Leonardo da Vinci proposed a double hull as a way to improve a ship's safety.
A double hull places an inner hull inside an outer hull, leaving a space between them. If the outer skin is damaged, the inner structure can help prevent water from reaching the vessel's interior. Modern tankers and some other vessels use double-hull construction for related protection against leaks and collisions.
Leonardo explored the idea in his studies of ships and naval engineering. His notebooks contain many proposals for improving vessels, including arrangements intended to make ships more resilient and useful in military or commercial settings.
Leonardo's proposal was not the same as a modern regulated tanker design. The historical sketch represents an early conceptual use of separated hull layers. It is also distinct from a catamaran, whose two hulls are separate side-by-side floating bodies rather than nested hulls.