Leonardo da Vinci proposed a double hull as a shipbuilding feature that could help a boat remain afloat after damage.
A double hull places a second layer of structure inside or around the outer hull, creating a space between them. If the exterior is breached, the inner hull can provide an additional barrier against flooding. Leonardo’s notebooks contain designs showing this protective principle for vessels.
The proposal reflects his interest in applying practical mechanics to military and transport problems. A stronger, more damage-resistant ship could be valuable in naval warfare, where collisions and attacks threatened a vessel’s buoyancy.
Leonardo’s idea should not be confused with a catamaran. A catamaran has two separate hulls side by side, while a double-hull vessel has an inner and outer hull arranged concentrically. Modern double hulls became especially familiar in tanker design, long after Leonardo’s sketches.