Leonardo da Vinci sketched a double-hulled ship, using two parallel hulls to improve stability and buoyancy. The arrangement is an early form of the twin-hull principle later used in catamarans and some modern ships.
Leonardo’s surviving notebooks contain many studies of naval engineering, including hull shapes, floats, and methods for limiting water entry. His double-hull concept was not a documented, full-size vessel built in his lifetime; it was a design study showing how separated hulls could make a craft steadier.
A double hull is not the same as a ship with an internal safety shell around one hull. Modern tankers use that latter arrangement to contain spills, whereas Leonardo’s drawing places two distinct buoyant bodies side by side. The design illustrates his habit of applying observations from nature and mechanics to practical transport problems.