What kind of hull did Leonardo da Vinci propose to make boats safer?

Leonardo da Vinci proposed a double hull to make boats safer against damage and leaking.

A double hull places a second layer of structure inside or outside the main hull, creating a space between the two surfaces. If the outer layer is breached, the inner layer can help keep water away from the vessel’s interior. Leonardo included this concept among his naval and engineering studies.

The idea was especially significant in an era when wooden boats were vulnerable to collisions, grounding, and battlefield damage. A protected inner shell could improve buoyancy and give a vessel more resistance to punctures. The sketch does not amount to a complete modern shipbuilding specification, so its exact intended use remains uncertain.

Double-hull construction later became important in submarines, tankers, and other specialized vessels. It should not be confused with a catamaran, which has two separate hulls side by side. Leonardo’s proposal concerned layered protection within one boat rather than two independent boats joined together.