Leonardo da Vinci sketched a double-hull concept, placing an inner hull within an outer hull to improve protection against damage.
The idea appears among his maritime studies and reflects his interest in applying engineering principles to ships. A separated outer layer could absorb some impact while helping keep the inner vessel watertight. This is the same broad protective logic later associated with double-hull construction.
Leonardo’s drawing was a design concept, not evidence that he built a modern-style tanker or proved the system at sea. Double hulls have different uses depending on the vessel. In modern oil tankers, the space between hulls helps protect cargo tanks during collisions or groundings; in other ships, it can contribute to buoyancy, strength, or compartmentalization.
The concept should not be confused with a reinforced keel, which strengthens the bottom centerline of a vessel. Leonardo produced many maritime sketches, including paddle-driven boats and underwater equipment, but each represented a separate design problem.