Leonardo da Vinci proposed a double hull to help a boat remain afloat after damage to its outer hull.
A double-hull design places an inner layer of structure inside an outer hull, creating a space between them. If the outer skin is breached, the inner hull can provide an additional barrier against flooding. Leonardo's notebooks include ideas for strengthening and protecting vessels through layered construction.
The concept reflects his broader interest in naval engineering and military technology. A protected hull could reduce the danger from collisions or deliberate attacks, although the Renaissance materials and construction methods would have made such a vessel difficult to build. The drawing is a design proposal, not evidence that Leonardo built a modern double-hulled ship.
A double hull is not the same as a catamaran. A catamaran has two separate hulls connected by a deck, while a double-hull vessel has one principal inner hull enclosed or protected by an outer hull. The safety principle is related, but the structures differ.