Leonardo da Vinci proposed using a double hull to protect ships.
His design placed an inner hull inside an outer hull, creating a space between them. The arrangement was intended to reduce the danger of a ship sinking if its outer shell was damaged. Leonardo’s idea anticipated a principle later used in ship construction and, in different forms, in some modern vessels.
The concept came from Leonardo’s practical studies of naval engineering, buoyancy, and structural strength. It was a proposal recorded in his notebooks, not evidence that he built a full-sized double-hulled vessel.
A double hull is not the same as two separate boats tied together. It is a layered construction in which the outer and inner walls form one vessel with a protective space between them.