Single hull is a ship construction term. In tankers with single hulls, oil in the cargo tanks is separated from the seawater only by a bottom and a side plate. Should this plate be damaged as a result of a collision or stranding, the contents of the cargo tanks risks spilling into the sea. An effective way of avoiding the risk is to surround the cargo tanks with a second internal plate which is at a sufficient distance from the external plate (generally 1.5-2 metres). This design, known as a double hull, safeguards cargo tanks from damage and thus reduces the risk of oil pollution. The double hull construction incorporates both double bottoms and double sides. An alternative solution is to have ships with double sides (double hull along the sides of the ship, an added side-shell plating structure fitted within the ship while the bottom of the ship has a single plate, a single bottom. This means that the cargo tanks are separated from the seawater only by a bottom plate. Double bottom, on the other hand, is a ship construction term referring to two separate but continuous and water-tight plating structures along some length and width of a ship's bottom