Leonardo da Vinci proposed a double-hulled ship design to reduce the danger of a hull being breached.
The concept placed two hull surfaces or layers around the vessel, creating additional protection against damage from impacts or collisions. If the outer skin were penetrated, the inner hull could help keep water away from the ship’s main interior spaces. This principle resembles the safety logic later used in some modern ships, although Leonardo’s design was a Renaissance proposal rather than a modern naval standard.
Leonardo studied boats, canals, locks, pumps, and water flow as connected engineering problems. His notebooks contain several maritime ideas, including vessels designed for speed, maneuverability, and military use. A double hull does not make a ship unsinkable, and its effectiveness depends on construction quality, compartmentation, and the location of damage.
The design is sometimes mistakenly described as a submarine because Leonardo also explored underwater devices. A double hull is instead a structural safety arrangement for a surface vessel.