Double Hull

A double hull is a ship construction in which the bottom and sides of the hull carry two complete watertight layers, an outer layer forming the vessel normal hull and an inner layer set some feet further in, so that damage to the outer layer alone does not breach the ship watertight integrity. Leonardo da Vinci first proposed a double-hulled ship design as protection against ramming and underwater damage from reefs or wreckage. The design ability to prevent or reduce oil spills led to its adoption for tankers and other vessel types under international maritime rules, most consequentially in the United States after the 1989 Exxon Valdez disaster, when the government required every new oil tanker built for use between American ports to carry a full double hull; the design does not, however, protect against the major high energy collisions or groundings that in fact cause most oil pollution incidents.