Leonardo da Vinci's double-hulled ship design used two layers of hull structure to improve protection against damage.
Leonardo drew a vessel with an inner hull enclosed by an outer hull, leaving a space between them. The arrangement was intended to make the ship more resistant if the outer skin was damaged. It also reflects his broader studies of naval engineering, including ship construction, propulsion, and methods for attacking vessels.
This design should not be confused with a submarine or a catamaran. A submarine is built for underwater operation, while a catamaran has two separate hulls that support a deck and are normally open between them. A double hull instead places one protective hull inside another. Leonardo's drawing is an early conceptual example; modern tankers and other ships use double hulls for safety, but their structures, materials, regulations, and engineering calculations are far more advanced.