Leonardo da Vinci proposed a double hull as a water-safety feature for ships.
His notebooks contain designs for boats with two layers or separate hull sections, an arrangement intended to reduce the danger of flooding after damage. The outer structure could take an impact while an inner layer helped keep water away from the vessel's main spaces.
Modern double-hull ships use a similar broad principle, especially oil tankers, where the space between hulls provides protection if the outer shell is breached. Leonardo's drawing was not a modern tanker specification and did not establish contemporary naval engineering. It is nevertheless an early recorded example of the idea that separated hull layers can improve survivability at sea.