Leonardo da Vinci’s leak-resistant ship concept was a double-hull ship.
Leonardo proposed placing one hull inside another, creating two layers of structure around the vessel. The concept was intended to improve strength and reduce the danger of water entering the ship if the outer hull was damaged. This is the same broad principle later associated with double-hull vessels.
The design reflects Leonardo’s interest in shipbuilding and naval engineering. His notebooks contain numerous studies of boats, water resistance, buoyancy, and mechanical propulsion. As with many of his engineering drawings, the surviving proposal is evidence of an idea rather than proof of a completed vessel built to his specifications.
Modern double hulls became especially important in oil tankers, where the second hull can help protect cargo tanks during some collisions or groundings. Leonardo’s proposal should not be confused with an ironclad, which is a warship protected by iron or steel armor, or with a submarine, which is designed to operate underwater.