Leonardo da Vinci designed a double hull with two separate layers intended to make a boat safer if the outer hull was damaged.
His notebooks contain ship designs that use an inner and outer hull, creating a protective space between them. The concept anticipates a principle used in later naval engineering: a second barrier can limit flooding after an impact or puncture. Leonardo’s broader studies included boats, canal systems, locks, pumps, and other hydraulic machines.
The design should not be mistaken for a catamaran. A catamaran has two distinct hulls supporting the vessel, whereas a double-hull ship has an inner hull within or alongside an outer hull. Leonardo’s drawings were proposals and studies, not evidence that he built a full-size double-hulled ship.
Modern double hulls became especially important in large ships and oil tankers. Their safety benefits are substantial but not absolute: collisions, grounding, structural failure, and flooding can still cause serious damage.