Leonardo da Vinci designed a double hull as a naval defense intended to reduce damage from cannon fire.
His ship studies included vessels with two layers of hull material separated by a space. The outer layer would take the impact of a projectile, while the inner layer could help preserve the ship’s watertight structure. This principle resembles the protective logic later used in some naval and maritime designs.
Leonardo’s proposal was not a modern steel double-hull tanker. It was a Renaissance wooden construction idea developed when naval artillery was changing ship design and warfare. There is no evidence that his particular double-hulled vessel became a standard working ship.
The double hull is also easily confused with a ship’s ballast arrangement or with an armored warship. Its defining feature is the presence of two hull layers, not merely extra weight, armor, or a second deck.