A jack-up rig or a self-elevating unit is a type of mobile platform that consists of a buoyant hull fitted with a number of movable legs, capable of raising its hull over the surface of the sea. The buoyant hull enables transportation of the unit and all attached machinery to a desired location. Once on location the hull is raised to the required elevation above the sea surface on its legs supported by the sea bed.
The legs of such units may be designed to penetrate the sea bed, may be fitted with enlarged sections or footings, or may be attached to a bottom mat. Generally Jackup rigs are not self propelled and rely on tugs or heavy lift ships for transportation.
Jack up platforms are used as exploratory drilling platforms and offshore and wind farm service platforms. Jackup platforms have been the most popular and numerous of various mobile types in existence. The total number of Jackup 'Drilling' rigs alone in operation number about 540 by the end of 2013.
Source: Wikipedia
