Dredging Boat and Derrick
An illustration of a dredging boat (right) and a derrick (left). A derrick is a lifting device composed of one mast or pole which is hinged freely at the bottom. It is controlled by lines (usually four of them) powered by some means such as man-hauling or motors, so that the pole can move in all four directions.
J. G. Holland, ed. Scribner's Monthly, An illustrated Magazine For the People (New York, NY: Scribner and Company, 1876)