What hull-safety feature did Leonardo da Vinci sketch for ships?

Leonardo da Vinci sketched a double hull as a hull-safety feature for ships.

A double hull places a second layer of structure inside the outer hull, creating a space between them. If the outer shell is damaged, the inner hull can help keep water away from the ship’s compartments. Leonardo included a related idea in his studies of naval engineering, showing his interest in improving ships’ resistance to leaks and collision damage.

Leonardo’s sketches did not create the modern commercial standard. Double hulls became especially important in later shipbuilding, including oil tankers, where international rules eventually required them for many vessels. The design can reduce the chance that a collision will immediately breach cargo tanks.

The feature is sometimes wrongly presented as a complete modern invention by Leonardo. A more accurate description is that he recorded an early double-hull concept; later engineers developed, tested, and regulated the technology in very different ships and conditions.