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A derrick is a lifting device composed of one mast or pole which is hinged freely at the bottom. It is controlled by (usually 4) lines powered by some such means as man-hauling or motors, so that the pole can move in all 4 directions. A line runs up it and over its top with a hook on the end, like with a crane. It was commonly used in docks.
The device was named after Thomas Derrick, an English executioner from the Elizabethan era because of its resemblance of the frame from which a hangman's noose hangs.
Derricks over drilled holes
Another kind of derrick is used over oil wells and other drilled holes.
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