What naval design did Leonardo da Vinci propose with two separate hulls joined by a deck?

Leonardo da Vinci proposed a double-hulled ship with two parallel hulls joined by a deck.

The arrangement was intended to improve stability and reduce the danger of a vessel capsizing. Leonardo explored many naval ideas, including hull shapes, propulsion systems, and methods for making ships more efficient. His double-hull concept anticipated a configuration later associated with catamarans and other multihull vessels.

A double-hulled ship has two distinct hulls, unlike a conventional single-hull vessel. The wider footprint can provide stability, although it also creates structural, steering, and hydrodynamic challenges. Leonardo’s drawing was a design study, not evidence that he built a successful modern catamaran.

The proposal is sometimes described loosely as a catamaran, but “double-hulled ship” is the more direct description of Leonardo’s invention. Modern catamarans developed through many later experiments and are not simply surviving copies of Leonardo’s drawing.