A derrick is a lifting device composed of one tower, or guyed mast such as a pole which is hinged freely at the bottom. A basic type of derrick is controlled by lines (usually four of them) connected to the top of the mast, powered by some means such as man-hauling or motors, so that the pole can move in all four directions. A separate line runs down from the top of the mast and over its bottom with a hook on the end, as with a crane for lifting the loads. There are also other types of derrick that may involve different ways to control the mast and a use of a boom. It is commonly used in docks and on board ships. Some large derricks are mounted on dedicated vessels, and are often known as "floating derricks".The term "derrick" is also used to call the tall framework that holds the drilling apparatus in an oil rig system.The device was named for its resemblance to a type of gallows from which a hangman's noose hangs. The derrick type of gallows in turn got its name from Thomas Derrick, an English executioner from the Elizabethan era.