Leonardo da Vinci proposed a double hull to help protect ships from leaks.
A double hull places an inner hull inside an outer hull, leaving a space between them. If the outer shell is damaged, the inner structure can remain watertight and reduce the chance of immediate flooding. Leonardo included this principle among his shipbuilding ideas.
The concept was not a complete modern ship design, and Leonardo did not build a vessel using it. His notebooks contain many studies of naval engineering, including hull forms, pumps and methods for moving water.
Double hulls later became important in several kinds of modern vessel. They are used in many tankers and other ships for safety and environmental protection, although the exact construction and regulations vary by vessel type. Leonardo’s proposal is therefore best understood as an early documented version of a structural safety principle, not as the invention of every modern double-hulled ship.