Leonardo da Vinci proposed a double hull as a ship-safety feature.
His naval drawings include vessels with two layers of hull structure, creating an inner and outer shell. The space between them could provide additional protection if the outer skin were damaged. The basic idea is similar to the safety principle later used in double-hulled ships and tankers.
Leonardo’s notebooks contain many studies of ships, water resistance, and naval engineering. These studies were often exploratory rather than records of completed construction. His double-hull concept should therefore be described as an early design proposal, not as a documented Renaissance shipbuilding standard.
A double hull is not the same as a catamaran. A catamaran has two separate side-by-side hulls that support a deck, whereas a double-hulled vessel has an outer hull surrounding or backing up an inner hull. Modern regulations have used double hulls to reduce pollution after tanker accidents.