Leonardo da Vinci proposed a double hull to help a vessel survive damage from flooding.
His ship designs included an inner hull separated from an outer hull, creating a protective space between them. The arrangement anticipated a principle later used in many ships: if the outer skin is breached, the inner barrier can continue keeping water away from vital compartments.
Leonardo developed numerous naval ideas while studying hydraulics, military engineering, and transport. His double-hull concept was not the same as the modern tanker regulations that require separate protective structures around cargo tanks. It was an early design proposal recorded in Renaissance notebooks rather than a documented, full-scale shipbuilding program.
The idea is also different from a catamaran, whose two hulls are separate side-by-side bodies connected by a deck. In a double-hull vessel, one hull is nested inside another. The concept later became important in ship safety and in oil-spill prevention, especially for tankers.