Leonardo da Vinci proposed a double hull as a shipbuilding feature to reduce the danger from leaks.
A double-hull vessel has two layers of structure separated by a space. If the outer skin is breached, the inner hull can remain intact and help keep water out of the main compartments. Leonardo’s ship designs included the idea of separating the external shell from the interior structure, anticipating a principle later used in specialized vessels.
This concept should not be confused with a double-ended boat or a ship with two parallel hulls, such as a catamaran. Modern double hulls are especially associated with oil tankers, where the outer layer provides additional protection against grounding or collision damage.