Leonardo da Vinci proposed a double hull as a naval safety feature for protecting a ship against leaks.
His maritime studies included the idea of constructing a vessel with two layers or hulls. The space between them could provide additional protection if the outer shell were damaged. This principle resembles the double-hull arrangement later used in some ships, especially tankers, to reduce the chance that a collision will breach cargo tanks directly.
Leonardo’s ship designs were part of a large body of engineering work covering canals, pumps, locks, and naval mechanisms. His drawings often explore alternative arrangements rather than presenting fully tested construction plans. Consequently, the double-hull idea should be credited as a documented proposal, not as a shipbuilding system he successfully introduced.
A double hull is different from a catamaran. A catamaran has two distinct hulls side by side, while a double-hull vessel generally has an inner hull within an outer hull.