Leonardo da Vinci proposed a double hull by separating a boat’s inner and outer shells to improve protection against damage.
The concept placed an additional layer around the main hull, creating a space between the two surfaces. Such separation can help keep water out if an outer section is breached and can also strengthen a vessel’s structure.
Leonardo’s maritime sketches include ideas for safer and more efficient boats, but his proposal should not be confused with a catamaran. A catamaran has two distinct hulls supporting one deck, whereas a double-hull vessel has nested or separated layers forming its hull system.
Double-hull construction became important much later in shipbuilding. Modern tankers use it to reduce the chance that cargo tanks will be punctured in a collision or grounding, although their designs are far more advanced than Leonardo’s sketches.