Leonardo da Vinci proposed a double hull as a protective feature for ships.
The concept places two hull layers around the vessel’s sides and bottom, leaving a space between them. If the outer shell is damaged, the inner hull can help keep water out and preserve buoyancy. Leonardo included the idea among his studies of naval engineering and ship design.
A double hull is a feature, not a complete vessel or propulsion system. Modern tankers use double hulls to reduce the chance that a collision or grounding will release cargo, while some ships use the space for ballast or structural protection.
Leonardo’s proposal did not create the modern shipping standard by itself. The historical importance lies in his early recognition that separating the water-exposed shell from the protected interior could improve survivability.