Leonardo da Vinci proposed a double hull to help a ship survive damage and reduce flooding.
A double hull places an additional layer of structure inside the outer hull, creating a protective space between them. Leonardo included the idea among his naval and engineering studies. The concept reflects his interest in compartmentalization and in preventing a single puncture from immediately filling the entire vessel with water.
The design should not be confused with a double-ended ship or a vessel with two separate hulls, such as a catamaran. A double hull is two layers around the same central vessel. Modern ships use double-hull construction for several reasons, including impact protection and containment of leaked cargo, although the exact details vary by ship type and regulation.
Leonardo’s proposal was a forward-looking sketch rather than a documented shipbuilding program that he completed. It is best understood as an early conceptual contribution to protective naval construction.