Leonardo da Vinci proposed a double hull as a way to improve a ship’s protection against damage.
A double hull places an inner hull inside an outer hull, leaving a space between them. If the outer layer were pierced, the second layer could help prevent water from immediately entering the vessel. Leonardo’s notebooks include ship designs associated with this protective idea centuries before double-hull construction became standard in some modern vessels.
The concept should not be confused with a catamaran. A catamaran has two separate hulls side by side, while a double-hull vessel has one hull enclosed within another. The space between layers can also be used for structural support or tanks in modern ships.
Leonardo’s drawing demonstrates his interest in applying geometry and mechanics to naval engineering, but it does not mean he invented every later form of double-hull ship.