Leonardo da Vinci proposed a double hull to protect a ship’s hull from underwater damage.
The concept placed an additional protective structure inside the outer hull, creating a space between layers. A puncture in the exterior would therefore not immediately open the vessel’s main interior to the water. Leonardo explored the idea in the context of shipbuilding and military engineering.
Double-hull construction later became important in several types of vessels, especially oil tankers, where the space between hulls helps reduce the risk of cargo release after a collision or grounding. Leonardo’s Renaissance proposal was not the same as a modern tanker design, however, and it did not establish the later engineering standards for ship safety.
A double hull should not be confused with a catamaran. A catamaran has two separate hulls joined by a deck, while a double-hull vessel has an inner and outer hull surrounding a protected space.