Leonardo da Vinci sketched a double hull as a ship feature intended to improve protection against damage.
A double hull places a second layer inside or around the outer hull, creating a space between the two structures. If the outer skin is breached, the inner layer can help preserve buoyancy and keep water from reaching the vessel’s central interior as quickly.
Leonardo included double-hull ideas among his studies of ships and naval engineering. The concept was not a modern steel tanker design in the contemporary sense; it was a Renaissance proposal showing how separated structural layers could improve safety.
The idea is sometimes confused with an outrigger, which is a side float or support attached outside a boat. A double hull instead relies on two hull surfaces or compartments arranged around the vessel itself.