Parts of a ship: Double Bottom Tanks

A double skin along the bottom of the ship (from a ship safety point of view these were not necessary in tankers with their smaller divided cargo spaces; however, from an environmental-safety consideration the American OPA 90 legislation has caused the new generation of tankers to have double skins). Its purpose is to provide a safeguard in the event of grounding, which happens to about two ships a day. This space is used for water ballast, fresh water or bunkers.