Leonardo da Vinci proposed a double hull by placing a second hull around the first for ship protection.
A double hull has two layers of hull material separated by a space. Leonardo included the idea in his studies of ships and naval engineering, imagining an outer layer that could reduce the danger from impact or damage to the inner hull.
The concept is important because the space between hulls can provide structural separation and, in later engineering, help contain water or cargo. Modern tankers use double hulls mainly to reduce oil spills after collisions or groundings, although their construction follows industrial standards far beyond Leonardo’s drawings.
Leonardo’s proposal should not be confused with an armored warship or a modern tanker design. His notebooks contain exploratory engineering ideas, and the double-hull concept was not a completed vessel that he launched.