Derrick
The most basic type of derrick is controlled by three or four lines connected to the top of the mast, which allow it to both move laterally and cant up and down.
To lift a load, a separate line runs up and over the mast with a hook on its free end, as with a crane.
The term derrick is also applied to the framework supporting a drilling apparatus in an oil rig.
The derrick tower can be a mast or a post with the bottom hinged at the base where all ropes meet.
The top of the mast is connected to many guy wires which are anchored to the ground to support the load.
The control of the lifting location is done by the manipulation of the top pulley system and the rotation of the mast at the base.
Another lashing between the fork area and the mast at a higher position supports the weight of the boom.
[7] A shearleg derrick is similar to a breast derrick with the exception that, instead of fixed guy wires that secure the top of the mast, it is secured by multiple reeved guys to permit handling loads at various radii by means of load tackle pulley system suspended from the mast top.
[2] In a simpler construction, a shearleg derrick can be assembled from two posts to form A-frame shear legs without any crossbar.
A sling, which may be made from ropes, is placed around the area that two legs meet to be used to put a tackle pulley system for lifting the load.
The boom is connected with the lower part of the mast which is shaped like a "Y" or a bipod and therefore it is a single swinging derrick.
On the cross trees, two guys are fastened using swivel outriggers which are stayed vertically and horizontally.
In order to maintain a good controlling angle between guys and derrick, the outriggers cannot pass the inboard parallel of the centerline.
The Universal Hallen derrick, replacing the D-Frame option, is a kind of traditional topping lift.
The D-Frame supersedes the outriggers and provides a good controlling angle on the guys.
The Hallen derrick is appropriate for, e.g., containers, logs, steel rail, sawn timber and heavy lifts.
As in the Hallen, the guys serve for topping and lowering the boom, but they are fastened on the yoke with four short, steel-wire hanger ropes.
It stems from the German shipyard HC Stülcken & Sohn, later taken over by neighboring yard Blohm & Voss.
The Stülcken can be made ready in few minutes (faster than a traditional heavy derrick), does not require much space, and is operated by four winches.
In the double-pendulum block type, half of the cargo tackle can be anchored to the base of the boom.
In order to double the hook speed, the halyard passes through the purchases since one end is secured, which reduces the safe working load by half.
