that was lowered more than a mile to the sea floor in attempts to stop the flow of oil in the Deepwater Horizon oil spill has been called a cofferdam. A cofferdam over 1 mile long was built to permit the construction of the Livingstone Channel in the Detroit River. See main article at Stony Island. Naval architecture A cofferdam may also refer to an insulating space between two watertight bulkheads or decks within a ship. A cofferdam can be a void (empty) space or a ballast space. Cofferdams are usually employed to ensure that oil or other chemicals do not leak into fresh water tanks which would result in contamination of the drinking water supply on the ship. The cofferdam would be empty at all times and the ship may have sensors within the cofferdam to warn if the cofferdam has begun to fill with liquid. If two different cargoes that react dangerously with each other are carried on the same vessel, one or more cofferdams are usually required between the cargo spaces. Portable cofferdams Portable cofferdams can be inflatable or frame and fabric cofferdams that can be reused. Inflatable cofferdams are stretched across the site, then inflated with water from the prospected dry area. Frame and fabric cofferdams are erected in the water and covered with watertight fabric. Once the area is dry, water still remaining from the dry area can be siphoned over to the wet area. See also Caisson, a similar watertight structure Dental dam References External links Dams by type Naval architecture