Leonardo da Vinci proposed a double hull as a protective structure for ships.
His maritime studies included the idea of placing an inner hull inside an outer hull, creating a space between them. This arrangement could reduce the chance that a collision or puncture would immediately open the vessel’s main internal compartment to the water. The concept appears among his many notes and sketches on ship design and naval engineering.
A double hull is not the same as simply making a ship’s outer planks thicker. It creates two separate layers, and the space between them can provide additional protection. Modern tankers and some other vessels use related principles, although their construction, materials, and safety rules are far more advanced.
Leonardo’s proposal should not be described as the invention of every modern double-hulled vessel. His notebooks contain exploratory designs rather than a documented production program. Nevertheless, the sketch shows that he recognized a major naval-engineering problem: separating the water outside a ship from the spaces needed to keep the ship afloat.