Leonardo da Vinci designed a double hull using two layers of construction to help protect a boat from leaks.
The double-hull concept places an inner hull inside an outer hull, creating a protective space between them. Leonardo included the idea among his naval and hydraulic studies. If the outside shell were damaged, the inner shell could help keep water from immediately entering the vessel.
This design is often confused with a catamaran. A catamaran has two distinct parallel hulls joined together, while a double-hull vessel has an inner and outer layer forming a protective barrier. The engineering principle is also different from simply strengthening a keel.
Double hulls later became important in modern shipbuilding, especially for oil tankers. International rules adopted after major tanker accidents made double hulls a key safety feature for many tankers, although Leonardo’s Renaissance proposal was not a modern regulated tanker design.