A derrick is a lifting device composed at minimum of one guyed mast , as in a gin pole , which may be articulated over a load by adjusting its guys . Most derricks have at least two components, either a guyed mast or self-supporting tower , and a boom hinged at its base to provide articulation, as in a stiffleg 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 .
51-398: Derricks are especially useful for high-rise rigging, jobs that cover a long period of time, or jobs when the impact to street or pedestrian traffic is a concern. Forms of derricks are commonly found aboard ships and at docking facilities. Large derricks mounted on dedicated vessels are known as floating derricks and shearlegs . The term derrick is also applied to the framework supporting
102-445: A block and fall: F a = L N 1 eff {\displaystyle F_{a}={\frac {L}{N}}{\frac {1}{\textit {eff}}}} where F a {\displaystyle F_{a}} is the force applied to the hauling part of the line (the input force), L {\displaystyle L} is the weight of the load (the output force), N {\displaystyle N}
153-412: 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
204-417: A dock may be created by building enclosing harbour walls into an existing natural water space, or by excavation within what would otherwise be dry land. There are specific types of dock structures where the water level is controlled: Where the water level is not controlled berths may be: A dockyard (or shipyard) consists of one or more docks, usually with other structures. In American English , dock
255-405: A drilling apparatus in an oil rig . The derrick derives its name from a type of gallows named after Thomas Derrick , an Elizabethan era English executioner . There are various types of derrick based on how the tower or mast is set up and the use of boom. 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
306-399: 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
357-432: A rope threaded through the pulleys is called tackle. The process of threading ropes or cables through blocks is called " reeving ", and a threaded block and tackle is said to have been "rove". A block and tackle system amplifies the tension force in the rope to lift heavy loads. They are common on boats and sailing ships , where tasks are often performed manually, as well as on cranes and drilling rigs , where once rove,
408-471: A tackle is offset by both the increased length of rope needed and the friction in the system. In order to raise a block and tackle with a mechanical advantage of 6 a distance of 1 metre, it is necessary to pull 6 metres of rope through the blocks. Frictional losses also mean there is a practical point at which the benefit of adding a further sheave is offset by the incremental increase in friction which would require additional force to be applied in order to lift
459-403: A traditional heavy derrick), does not require much space and is operated by four winches. The Stülcken is secured between two V-shaped, unstayed Samson-posts . This makes it possible to let the derrick swing through the posts to reach another hatch. Each post has a hoisting winch, a span winch and a lever that is run by one man only. The span tackles are independent and the halyard is endless. With
510-431: Is a steel bracket welded on the mast in the centerline. For an observer standing a beam , the frame has a "D"-shape. 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. It does not lend itself to small, general cargo. It keeps the deck clear of guy ropes and preventors. Only one winchman
561-525: Is a third winch to hoist to cargo on the yoke. Runners decrease swing and rotation of the cargo. A joystick duplex controller steers the Velle derrick. The Stülcken derrick is used for heavy cargo. It stems from the German shipyard HC Stülcken & Sohn , later taken over by neighboring yard Blohm & Voss . This derrick can handle up to 300 tonnes . The Stülcken can be made ready in few minutes (faster than
SECTION 10
#1732791906964612-463: Is able to swing through, which allows the lower blocks to swing freely to each side of the boom. In this way the derrick can reach a vertical position. A bullrope pulls the derrick to the other side until the weight of the cargo tips the derrick over, so that the span tackles now have the weight on the other side. The union table is fixed again and the derrick can start work on the other side. There are also Stülcken with single-pendulum blocks. In this type
663-467: Is also commonly used to refer to wooden or metal structures that extend into the ocean from beaches and are used, for the most part, to accommodate fishing in the ocean without using a boat. In American English , the term for the water area between piers is slip . In the cottage country of Canada and the United States , a dock is a wooden platform built over water, with one end secured to
714-409: Is also used on some offshore oil and gas rigs. 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
765-405: Is available. 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
816-399: Is characterized by the use of a single continuous rope to transmit a tension force around one or more pulleys to lift or move a load. Its mechanical advantage is the number of parts of the rope that act on the load. The mechanical advantage of a tackle dictates how much easier it is to haul or lift the load. If frictional losses are neglected, the mechanical advantage of a block and tackle
867-425: Is equal to the number of parts in the line that either attach to or run through the moving blocks—in other words, the number of supporting rope sections. An ideal block and tackle with a moving block supported by n rope sections has the mechanical advantage (MA), M A = F B F A = n , {\displaystyle MA={\frac {F_{B}}{F_{A}}}=n,\!} where F A
918-404: Is lifted by another pulley system connected to the top of the boom. 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
969-487: Is needed, and the Hallen can be brought into use within a few minutes. It is less expensive than a crane. A disadvantage is the low working range of the Hallen derrick; it is able to swing 75° from the centerline and can work against a list of up to 15°. The Velle derrick is similar to the Hallen but without the use of outriggers. On top of the boom is a T-shaped yoke . As in the Hallen, the guys serve for topping and lowering
1020-601: Is possible by use of the sheave friction factor, K {\displaystyle K} (which may be obtainable from the manufacturer or published tables ). The relevant equation is: eff = K N − 1 K S N ( K − 1 ) . {\displaystyle {\textit {eff}}={\frac {K^{N}-1}{K^{S}N(K-1)}}.} Typical K {\displaystyle K} values are 1.04 for roller bearing sheaves and 1.09 for plain bearing sheaves (with wire rope). The increased force produced by
1071-460: Is technically synonymous with pier or wharf —any human-made structure in the water intended for people to be on. However, in modern use, pier is generally used to refer to structures originally intended for industrial use, such as seafood processing or shipping , and more recently for cruise ships , and dock is used for almost everything else, often with a qualifier, such as ferry dock , swimming dock, ore dock and others. However, pier
SECTION 20
#17327919069641122-425: Is the hauling (or input) force and F B is the load. Consider the set of pulleys that form the moving block and the parts of the rope that support this block. If there are n of these parts of the rope supporting the load F B , then a force balance on the moving block shows that the tension in each of the parts of the rope must be F B /n. This means the input force on the rope is F A = F B /n. Thus,
1173-444: Is the ideal mechanical advantage of the system (which is the same as the number of segments of line extending from the moving block), and eff {\displaystyle {\textit {eff}}} is the mechanical efficiency of the system (equal to one for an ideal frictionless system; a fraction less than one for real-world systems with energy losses due to friction and other causes). If S {\displaystyle S}
1224-440: Is the most efficient use of equipment and resources. For example, if the load is to be hauled parallel to the ground, reeving to advantage enables the pulling force to be in the direction of the load movement, allowing obstacles to be managed more easily. Reeving to disadvantage adds an extra sheave to change the direction of the pulling line to a potentially more ergonomic direction, which increases friction losses without improving
1275-539: Is the number of sheaves in the purchase, and there is a roughly x {\displaystyle x} % loss of efficiency at each sheave due to friction, then: 1 eff ≈ 1 + S x 100 . {\displaystyle {\frac {1}{\textit {eff}}}\approx 1+S{\frac {x}{100}}.} This approximation is more accurate for smaller values of S {\displaystyle S} and x {\displaystyle x} . A more precise estimate of efficiency
1326-422: Is threaded through the pulleys to provide mechanical advantage that amplifies the force applied to the rope. Hero of Alexandria described cranes formed from assemblies of pulleys in the first century. Illustrated versions of Hero's Mechanica (a book on raising heavy weights) show early block and tackle systems. A block is a set of pulleys or sheaves mounted on a single frame. An assembly of blocks with
1377-466: The Gulf of Khambhat has the highest tidal amplitude and ships can be sluiced through flow tides in the river estuary . The engineers built a trapezoidal structure, with north–south arms of average 21.8 metres (71.5 ft), and east–west arms of 37 metres (121 ft). In British English , a dock is an enclosed area of water used for loading, unloading, building or repairing ships . Such
1428-515: The Red Sea coast. Archaeologists also discovered anchors and storage jars near the site. A dock from Lothal in India dates from 2400 BC and was located away from the main current to avoid deposition of silt . Modern oceanographers have observed that the ancient Harappans must have possessed great knowledge relating to tides in order to build such a dock on the ever-shifting course of
1479-464: The Sabarmati , as well as exemplary hydrography and maritime engineering . This is the earliest known dock found in the world equipped to berth and service ships. It is speculated that Lothal engineers studied tidal movements and their effects on brick-built structures, since the walls are of kiln -burnt bricks. This knowledge also enabled them to select Lothal's location in the first place, as
1530-451: The block and tackle reduces the input force by the factor n. Ideal mechanical advantage correlates directly with velocity ratio . The velocity ratio of a tackle is the ratio between the velocity of the hauling line to that of the hauled load. A line with a mechanical advantage of 4 has a velocity ratio of 4:1. In other words, to raise a load at 1 metre per second, the hauling part of the rope must be pulled at 4 metres per second. Therefore,
1581-415: 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. A shearleg derrick is similar to a breast derrick with
Derrick - Misplaced Pages Continue
1632-403: The boom, but they are fastened on the yoke with four short, steel-wire hanger ropes. The ends of the topping and lowering ends of the halyard are secured to half-barrels on one winch. In this way the boom moves at the same speed as the winch veers the topping end of the halyard and hauls the lowering end of the halyard, and vice versa. The slewing ends are also wound on to another half-barrel. There
1683-414: 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
1734-416: The bottom ends of the stifflegs and the base of the mast. There may be a counterweight to place on the sills behind the stifflegs in heavy load lifting. A stiffleg derrick on a vessel is called a floating stiffleg derrick. Another kind of derrick is used on oil wells and other drilled holes. Both the structure itself and the complex set of machines associated with it are referred to as a derrick. A derrick
1785-536: The cargo hook is detached and the lower and upper cargo block are hauled into the center of the Stülcken. To tip the derrick over, gravity is used again. Dock (maritime) The word dock (from Dutch dok ) in American English refers to one or a group of human-made structures that are involved in the handling of boats or ships (usually on or near a shore ). In British English ,
1836-402: 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. 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
1887-400: 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 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
1938-401: The inboard parallel of the centerline. The right outrigger stays in the centerline while the left outrigger moves outboard. This derrick will lower or heave cargo as both guys are veered or hauled. Three winches, controlled by joystick, are necessary to operate the Hallen derrick: two for the guys and one for the purchase. Limit switches are used to avoid an over-topping or over-swinging. However,
1989-491: The limits can be modified if a different working range or a special vertical stowage is required. The safe working load of the Hallen is between 10 and 80 tonnes. In a Hallen Universal derrick, which has no Hallen D-Frame, the halyard has an extended length since it runs through further blocks on the centerline. The Universal Hallen derrick, replacing the D-Frame option, is a kind of traditional topping lift. The Hallen D-Frame
2040-501: 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. 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 tensile or compressive forces . Sills may also be used to connect between
2091-452: 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. 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
Derrick - Misplaced Pages Continue
2142-413: The mechanical advantage of a double tackle is 4. The mechanical advantage of any tackle can be increased by interchanging the fixed and moving blocks so the rope is attached to the moving block and the rope is pulled in the direction of the lifted load. In this case the block and tackle is said to be "rove to advantage." Diagram 3 shows three rope parts supporting the load W , which means the tension in
2193-420: The revolving suspension heads on the posts it takes ten minutes to swing all the way through. 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. After the union table is detached, the double-pendulum block type of Stülcken
2244-476: The rope is W/3 . Thus, the mechanical advantage is three-to-one. By adding a pulley to the fixed block of a gun tackle the direction of the pulling force is reversed though the mechanical advantage remains the same, Diagram 3a. This is an example of the Luff tackle. The decision of which to use depends on pragmatic considerations for the total ergonomics of working with a particular situation. Reeving to advantage
2295-404: The shore. The platform is used for the boarding and offloading of small boats. Block and tackle A block and tackle or only tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift heavy loads. The pulleys are assembled to form blocks and then blocks are paired so that one is fixed and one moves with the load. The rope
2346-403: The tasks are performed by heavy equipment. In the diagram shown here, the number of rope sections of the tackles shown is as follows: Note that in the gun tackle, double tackle and threefold purchase, both blocks have the same number of pulleys (one, two and three, respectively) whereas the Luff tackle and Gyn tackle have mis-matched blocks with differing numbers of pulleys. A block and tackle
2397-679: The term is not used the same way as in American English; it is used to mean the area of water that is next to or around a wharf or quay. The exact meaning varies among different variants of the English language . "Dock" may also refer to a dockyard (also known as a shipyard ) where the loading, unloading, building, or repairing of ships occurs. The earliest known docks were those discovered in Wadi al-Jarf , an ancient Egyptian harbor , of Pharaoh Khufu , dating from c.2500 BC located on
2448-410: 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 reeved guys to position the top of the tower to the desired location by varying the length of
2499-438: 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. 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,
2550-405: The upper guy lines. The load is lifted using a pulley system connected to the top of the tower. 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. A Chicago boom derrick is a derrick with
2601-414: The velocity ratio. Situations in which reeving to disadvantage may be more desirable include lifting from a fixed point overhead--the additional pulley allows pulling downwards instead of upwards so that the weight of the lifter can offset the weight of the load, or allows pulling sideways, enabling multiple lifters to combine effort. The formula used to find the effort required to raise a given weight using
SECTION 50
#1732791906964#963036