Leonardo da Vinci proposed a double hull to help ships remain afloat after damage.
The concept placed an additional layer of wood inside the outer hull, creating a protective space between the two surfaces. If the exterior were breached, the inner structure could reduce the amount of water entering the vessel and preserve buoyancy.
Leonardo explored the idea in the context of ship design and water management. His notebooks contain many studies of boats, pumps, locks, canals, and the behavior of water. These investigations show that his engineering interests extended well beyond painting and flying machines.
A double hull is not the same as a watertight bulkhead. Modern ships may use both: a second shell protects against some external damage, while bulkheads divide the interior into compartments. The basic principle remains important in naval architecture and tanker safety.