Leonardo da Vinci proposed a double hull by placing two protective layers around a boat’s interior.
His notebooks include marine designs that use separated hull structures to improve protection against collision or damage. The basic idea is simple: if an outer hull is breached, an inner hull can help keep water away from the vessel’s central space. This is the same broad safety principle later used in many ships and tankers.
Leonardo’s proposal was a conceptual design from the Renaissance, not a modern regulated shipbuilding standard. It should not be confused with a catamaran, whose two hulls are primarily a form of flotation and stability. A double hull can have two layers or shells even when the vessel is not a two-hull craft.
Modern double-hull requirements developed centuries later for particular classes of ships, especially oil tankers. Leonardo’s drawing is notable because it anticipates the value of structural redundancy in marine safety.