Derricks And Cranes

Derricks And Cranes
Derricks and Cranes are both ship terms related to lifting appliances. Derricks are now relics of the past and found only on a few older ships. They have been replaced by the more versatile and much simpler Deck Crane.
Derricks are lifting devices composed of one or more guy masts (supporting members). A derrick is controlled by several lines connected to the top of the mast, which controls the lateral and vertical motion of the derrick. The runner-up/down function to lift and lower a load is accomplished by a separate line similar to a crane.
The most popular derrick on ships is the Union Purchase Rig, which uses two derricks, enabling the operators to load and discharge cargo much faster than single derricks.
One of the major disadvantages of the Derrick is that it takes longer to change the rig to suit different cargo types and lifts. The operation of derricks also requires at least two winch operators.
Cranes are similar to derricks but are much simpler in operation. A single crane driver accomplishes all functions – Runner up / down, Boom Up / Down, Swinging sidewards, etc. Most shipboard cranes are designed to swing through 360 degrees but may also have safety limit switches which prevent cranes from operating at angles which can cause damage to structures. Limit switches are also provided to prevent the runner wire from reaching the end of the drum.