Leonardo da Vinci proposed a double hull to make vessels safer after hull damage.
His ship designs included an inner and outer hull separated by a space. The arrangement was intended to reduce the danger of water entering the vessel if the outer skin was breached. Leonardo applied the idea to naval engineering while considering ship structure, buoyancy, and survivability.
A double hull is not the same as a ballast keel, which adds stability below a vessel, or a watertight bulkhead, which divides the inside of a ship. Modern oil tankers commonly use double hulls, but their structures and regulations belong to a much later era. Leonardo's proposal was an early expression of the same protective principle.