What dual-hulled ship design did Leonardo da Vinci propose to improve resistance to flooding?

Leonardo da Vinci proposed a double-hull ship design to improve resistance to flooding.

The concept placed an additional layer of structure inside or alongside the outer hull. If the outer skin were damaged, the second barrier could reduce the chance that water would immediately reach the vessel’s interior. Leonardo explored the idea as part of his broader studies of ships, canals, and military engineering.

A double hull is a structural arrangement, not a single named vessel. Modern ships use double hulls for several reasons, including protection against accidental grounding and collision. Tankers in particular became associated with double-hull requirements because the extra barrier can reduce oil spills after damage.

Leonardo’s proposal did not create modern maritime safety rules, and his design should not be confused with a catamaran. A catamaran has two separated hulls supporting a deck, whereas a double-hull ship generally has one main hull with a second protective skin or internal hull.