Leonardo da Vinci proposed a double hull as a safety feature for ships.
His ship designs included an inner hull and an outer hull, creating a space between them. The arrangement was intended to improve strength and reduce the danger of flooding if the outer shell was damaged. Separating the hull into compartments also reflects Leonardo's broader interest in applying structural ideas from architecture and engineering to watercraft.
A double hull is not the same as a catamaran. A catamaran has two separate, side-by-side hulls connected by a deck, whereas a double-hull ship has two layers forming one vessel. Modern tankers and some other ships use double hulls to help contain leaks and protect cargo tanks.
Leonardo's proposal was not a standardized maritime technology of his time. It was part of a group of theoretical naval and hydraulic designs preserved in his notebooks. The concept shows that he recognized the value of redundancy and compartmentalization long before these became important principles of modern ship design.