Leonardo da Vinci designed a ship with two separate layers forming a double hull.
The double-hull concept appears among Leonardo’s naval and water-engineering studies. A second hull could provide additional protection if the outer layer were damaged, although the surviving design should be understood as a proposal rather than as proof of a completed vessel.
Leonardo examined ships from practical, military, and structural perspectives. His notebooks include studies of hull construction, propulsion, canals, and methods for moving vessels through water. The double-hull idea belongs to this wider body of maritime engineering rather than to a single documented shipyard project.
The design is sometimes confused with a catamaran, which has two parallel hulls side by side. Leonardo’s concept is described as a double hull, meaning layered protection around the vessel, not simply two independent hulls joined together.