Leonardo da Vinci proposed a double hull to help protect a ship when its outer hull was damaged.
A double-hull vessel has two layers of hull structure separated by a space. Leonardo’s maritime studies included the idea of an inner layer that could provide additional protection against leaks caused by impact or other damage. The concept is related to the broader engineering principle of separating an outer shell from a protected interior.
This should not be confused with a catamaran, which has two separate hulls side by side for stability and speed. A double hull is a layered arrangement within the same vessel design. Modern ships may use double hulls for different reasons, including collision protection and pollution prevention, but those later applications do not mean Leonardo built a modern tanker.
Leonardo’s proposal remained a design concept. Its historical importance lies in showing that he recognized the value of redundancy and compartmentalized protection in marine engineering long before such structures became common in shipbuilding.