Leonardo da Vinci proposed a double hull as a shipbuilding feature intended to improve protection against leaks and damage.
A double hull places an inner hull inside an outer hull, creating a space between them. If the outer skin is breached, the inner structure can help keep water away from the vessel’s main interior. Leonardo’s notebooks contain an early proposal for this general principle.
The idea is often associated with modern tankers, where double hulls became important for reducing oil-spill risk after collisions and groundings. Modern double-hull construction is much more advanced than Leonardo’s sketch and uses materials, compartments, and engineering standards unavailable in the Renaissance.
A double hull is not the same as a catamaran. A catamaran has two separate side-by-side hulls connected by a structure, whereas a double-hull ship has one vessel with an outer and inner hull arrangement.