Leonardo da Vinci’s double-hull design used two layers of ship structure to help protect a vessel from leaks. His notebooks contain ship concepts with an inner and outer hull separated by a space.
The principle is similar to modern double-hull construction: if the outer skin is damaged, the inner hull may remain watertight. Leonardo also explored related naval ideas, including improved hull forms and mechanisms for moving vessels. His drawings do not represent one standardized ship model, so the double hull is best understood as a design principle rather than a single completed vessel.
The idea is often confused with ballast, which adds weight low in a ship to improve stability. A double hull primarily creates protective separation; it does not perform the same function as ballast. Modern tankers and other vessels use double-hull structures for damage protection, though their materials, regulations, and engineering differ greatly from Renaissance practice.
Leonardo’s sketches show that he recognized the value of redundancy in marine construction centuries before it became common naval engineering.