What Leonardo da Vinci invention used two layers of wood to protect a boat from leaks?

Leonardo da Vinci's double-hulled boat used two layers of wood to help protect a vessel from leaks. His sketches explored a second hull or internal protective layer that could improve a boat's resistance to damage.

The concept belongs to Leonardo's broad studies of watercraft and hydraulic engineering. A separated outer and inner structure could provide additional protection if the outside were struck or damaged. The design also reflects his habit of treating boats as systems of buoyancy, structural strength, and water flow.

This idea should not be confused with the modern double-hull requirement used for many oil tankers. Modern ships use carefully engineered compartments, materials, and safety standards developed over centuries. Leonardo's sketch was an early conceptual design, not a modern naval specification.

Leonardo produced numerous drawings of boats, canals, locks, pumps, and methods for moving on water. Some were practical improvements, while others were speculative. The double-hulled boat is important because it anticipates a principle later used in ship safety, even though no complete Leonardo prototype is known.