Leonardo da Vinci designed a double-hull ship as an underwater defense against enemy vessels.
The concept placed an inner hull inside an outer hull, creating a protected layer between them. Leonardo’s shipbuilding studies explored ways to reduce the danger of damage below the waterline. A separated hull arrangement could potentially keep a vessel afloat after an outer section was breached.
Leonardo did not build a working ship from the design, and his drawings do not establish that the concept was tested at sea. The idea is therefore best described as an early marine-engineering proposal, not as a successful historical vessel.
A double hull is also a modern shipbuilding term, especially for tankers, but modern double-hull ships use engineered compartments, structural standards, and materials unavailable to Leonardo. His drawing should not be treated as a direct prototype of every later double-hull vessel.