Derricks. Greymouth NZ
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". Original public domain image from Flickr