What safety feature did Leonardo da Vinci propose for a ship’s hull?

Leonardo da Vinci proposed a double hull as a safety feature for ships.

His maritime studies included a vessel with two layers of hull material, creating a protective space between the outer and inner surfaces. The arrangement was intended to reduce the danger of flooding if the outside hull was pierced. This is the same broad principle later used in double-hulled ships and some modern vessels.

Leonardo’s proposal appeared centuries before double-hull construction became an established maritime practice. It should not be confused with a catamaran, whose two hulls are separate side-by-side bodies that support the vessel. Leonardo’s design placed one hull within another.

The idea illustrates his habit of treating engineering problems through layered structures and mechanical safeguards. His notebooks contain many maritime proposals, but most were designs and studies rather than ships known to have been built under his supervision.