Leonardo da Vinci proposed a double hull as a form of ship protection.
Leonardo’s maritime studies included vessels with two layers or parallel hull structures. The concept could protect a ship’s interior from damage by placing an additional barrier between the sea and the main compartments. It also reflects his interest in improving buoyancy, stability, and resistance to attack.
A double hull is not the same as a catamaran. A catamaran has two separated hulls that normally support a shared deck, while a double-hull arrangement can place one protective hull around or alongside another. Modern tankers use double hulls mainly to reduce oil spills after collisions or groundings.
Leonardo’s proposal was part of a broad collection of naval and hydraulic designs. Many of his ship ideas remained drawings rather than tested vessels, so their practical performance cannot be assumed from the sketches alone.