Editing Derrick (section)

== Types ==
There are various types of derrick based on how the tower or mast is set up and the use of boom.<ref name=osha/>

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=== A-frame  ===
[[File:A-frame derrick.gif|thumb|A-frame derrick]]
An A-frame derrick is one in which the boom is hinged from a cross member between the bottom ends of two upright members spread apart at the lower ends and joined at the top; the boom point secured to the junction of the side members, and the side members are braced or guyed from this junction point.<ref name=osha/><ref name="calif2" />

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=== Basket ===
[[File:Basket derrick.gif|thumb|Basket derrick]]
A basket derrick is a derrick without a boom that is supported by a rope-and-pole system that forms a basket. The basket is constructed from a group of poles to form a [[polygon]]. There are crossbars between the pole members to strengthen their support. The supporting ropes are tied to the top of the basket poles on one end and joined together on the other end at a lower elevation than the top of the basket poles to form the base for the derrick tower. 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 tower is secured with multiple [[Glossary of nautical terms (M–Z)#reeve|reeved]] guys to position the top of the tower to the desired location by varying the length of the upper guy lines. The load is lifted using a pulley system connected to the top of the tower.<ref name=osha/>

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=== Breast ===
[[File:Breast derrick.gif|thumb|Breast derrick]]
A breast derrick is a derrick without a boom and with a mast constructed from two upright members. The upright members are more spread at their bottom ends than their top ends. There are crossbars to join the two members from the bottom to the top to form a mast.<ref name=osha/><ref name="calif2" />

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=== Chicago boom ===
[[File:Chicago boom derrick.gif|thumb|Chicago boom derrick]]
A Chicago boom derrick is a derrick with a boom which is attached to an external structure. The external upright member of the structure serves as the mast, and the boom is stepped in a fixed socket clamped to the upright. The boom is connected to at least three pulley systems to control the position of the boom. For example, a pulley system is connected to the top of the boom and the higher area of the external structure and two pulley systems near the top of the boom connected on either side of the boom to the external structure. The position of the top of the boom can be controlled by manipulating these pulley systems. The load is lifted from a separate pulley system that is connected to the top of the boom.<ref name=osha/><ref name="calif2" />

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=== Gin pole ===
[[File:Gin pole derrick.gif|thumb|Gin pole derrick]]
{{Main|Gin pole}}

A gin pole derrick (also known as standing derrick or pole derrick) is a derrick without a boom and with single tower or mast supported by four guy wires (two side guys, a fore guy and a rear guy). Its guys are so arranged from its top as to permit leaning the mast in any direction. The base of the tower is hinged and the top of the tower is connected to a pulley system for load lifting. As this is a simple derrick system, it is recommended for use by some agencies as an improvised rescue derrick in an emergency situation where no suitable rescue derrick or crane is available.<ref name=au/><ref name=osha/>

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=== Guy ===
{{multiple image
|image1=Guy derrick.gif
|caption1=Guy derrick
|image2=Guy derrick with nonrotatable mast.gif
|caption2=Guy derrick with non-rotatable mast}}

A guy derrick (also known as boom derrick) is a fixed guyed mast derrick that can be rotated and connected to a boom. The mast is in upright position with the base that can make the mast rotate, but not lean in any direction. The top of the mast is connected to many guy wires which are anchored to the ground to support the load. At the base, the mast is also connect to the bottom end of the boom. The boom extends outward and upward to the desired position. The top of the boom is a pulley system that is connected to the top of the mast to control how far the boom is to be from the mast. When the mast is rotated, the connected boom is swung from to the side. 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. The load is lifted by another pulley system connected to the top of the boom.<ref name="osha" /> In a medium load lifting, another construction method can be used. In this case, the mast is fixed without being rotated, but the boom can be swung around the mast. This can be done by connecting the bottom of the boom with two boards on the opposite sides around the surface of the boom to form a fork. The fork and the bottom part of the boom are lashed to secure them together. Another lashing between the fork area and the mast at a higher position supports the weight of the boom. The fork is put around the mast such that the bottom of the boom rests on the mast without being permanently fixed to it. The fork prevents the boom from coming off the mast while it swings up to 180 degrees.<ref name=usarmy>{{cite book|title=Field Manual 5-125 - Rigging Techniques, Procedures, and Applications|date=3 October 1995|publisher=The United States Army|url=http://library.enlisted.info/field-manuals/series-1/FM5_125/CH5.PDF|access-date=6 July 2014|archive-url=https://web.archive.org/web/20120813042250/http://library.enlisted.info/field-manuals/series-1/FM5_125/CH5.PDF|archive-date=13 August 2012|url-status=usurped}}</ref>

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=== Shearleg ===
{{Further|Shear legs}}

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 [[Block and tackle|load tackle]] pulley system suspended from the mast top.<ref name="osha" /> In a simpler construction, a shearleg derrick can be assembled from two posts to form A-frame shear legs without any crossbar. The bottom of the legs are set in two holes on the ground, spreading them apart. There is a rope to tie the two legs together near the bottom to prevent them from spreading apart further. On the top side, the two legs are connected together by a [[Lashing (ropework)|lashing]] but with a small spacer block placed between the legs. 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. There are two guy wires, front and rear, to support the shear legs. The rear guy may be reeved to allow adjustment of the angle of the shear legs.<ref name=usarmy/>

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=== Stiffleg ===
[[File:Stiffleg derrick.gif|thumb|Stiffleg derrick]]

A stiffleg derrick, also known as a Scotch derrick, is a derrick with a boom similar to that of a guy derrick, but instead of using guy wires to secure the top of the mast, it uses two or more stiff members, called stifflegs, which are capable of resisting either [[Tension (physics)|tensile]] or [[Compression (physics)|compressive forces]]. [[Sill plate|Sills]] may also be used to connect between the bottom ends of the stifflegs and the base of the mast.<ref name="osha" /> There may be a [[counterweight]] to place on the sills behind the stifflegs in heavy load lifting.<ref name="usarmy" /> A stiffleg derrick on a vessel is called a floating stiffleg derrick.<ref name="calif2" />

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