Leonardo da Vinci proposed a double hull as a ship feature intended to improve protection against sinking.
A double hull places an additional layer of structure inside or around the outer hull, creating a space between the two shells. Leonardo’s maritime studies included this idea as part of his broader investigations into ship design, water flow, and naval engineering.
The concept could provide extra protection if the outside of a vessel were damaged. It also relates to the general engineering principle of separating a vulnerable outer surface from an inner pressure- or cargo-containing structure. Modern tankers and some other ships use double-hull construction, although their materials, regulations, and structural calculations differ greatly from Leonardo’s Renaissance proposal.
A double hull is not the same as a reinforced keel. The keel is a central longitudinal structural member, while a double hull describes two layers of hull structure. Leonardo made many maritime proposals, and the double-hull idea is one of the clearest examples connected with later ship-safety engineering.