Which Leonardo da Vinci design is considered an early double-hulled ship concept?

Leonardo da Vinci designed an early double-hull ship concept with two layers of protection against water entering the vessel.

A double hull places an inner hull inside or alongside an outer hull, creating a space between them. Leonardo's naval studies explored this arrangement as a way to improve a ship's resistance to damage. If the outer shell were breached, the inner structure could help keep the vessel afloat, at least in principle.

The concept belongs to Leonardo's broad interest in water engineering, which also included canals, locks, pumps, and boats. His notebooks do not represent a single finished shipyard blueprint; they contain experiments, alternative sketches, and mechanical studies developed for different patrons and problems.

Modern double-hull ships became especially important in oil tankers and other vessels because separated hull structures can reduce the chance of cargo escaping after a collision or grounding. Leonardo's design should not be confused with the later standardized engineering of those ships. It is an early conceptual exploration, not proof that he built a modern double-hull vessel.