Leonardo da Vinci proposed a double hull as a shipbuilding safety feature.
The concept placed an additional layer of hull structure around the vessel, creating protection against damage and helping keep water from immediately flooding the ship. This was a remarkably early anticipation of a principle later used in specialized ships and tankers.
Leonardo’s ship designs formed part of his wider studies of naval engineering, buoyancy, and water transport. His notebooks contain many proposals, and the double-hull idea should be treated as a documented design concept rather than evidence that he built a modern double-hulled vessel.
A double hull is not the same as a catamaran. A catamaran has two separate, generally parallel hulls supporting a deck, whereas a double-hull arrangement usually means an inner and outer hull surrounding protected space.