"Sheers" redirects here. For other uses, see Sheer.
Shear legs, also known as sheers, shears, or sheer legs, are a form of two-legged lifting device. Shear legs may be permanent, formed of a solid A-frame and supports, as commonly seen on land and the floating sheerleg, or temporary, as aboard a vessel lacking a fixed crane or derrick.
Sheerlegs mounted on an M32 tank recovery vehicle
When fixed, they are often used for very heavy lifting, as in tank recovery, shipbuilding, and offshore salvage operations. At dockyards they hoist masts and other substantial rigging parts on board.[1] They are sometimes temporarily rigged on sailboats for similar tasks.
Shear legs are a lifting device related to the gin pole, derrick and tripod (lifting device). Shears are an A-frame of any kind of material such as timbers or metal, the feet resting on or in the ground or on a solid surface which will not let them move and the top held in place with guy-wires or guy ropes simply called "guys". Shear legs only need two guys whereas a gin pole needs at least three. The U. S. Army Field Manual FM 5-125 gives detailed instruction on how to rig shears.[2]
Fixed shear legs are most commonly found on floating cranes known as floating sheerlegs. These have heavy A-frame booms and vary in lifting capacity between 50 and 4,000 tons, and are used principally in shipbuilding, other large scale fabrication, cargo management, and salvage operations.
Temporary sheers comprise two upright spars, lashed together at their heads and their feet splayed apart. Unlike in a gyn, which has three legs and is thus stable without support, stability in sheers (derricks, and single-legged gin poles) is provided by a guy.[3] The heels of the spars are secured by splay and heel tackles. The point at the top of the sheers where the spars cross and are lashed together is the "crutch", to which a block and tackle is attached. Unlike derricks, sheers need no lateral support, and only require either a foreguy and an aftguy or a martingale and a topping lift. Being made of two spars rather than one, sheers are stronger than a derrick of the same size and made of equivalent materials. Unlike the apex of a gyn, which is fixed, the crutch of a sheers can be topped up or lowered, via the topping lift, through a limited angle.[4] In the era of sailing vessels, it was common for dockyards to employ a sheer hulk, an old floating ship's hull fitted with sheer legs, and used to install masts in other ships.
Look up shear legs in Wiktionary, the free dictionary.
References
^Robert Kipping (1854). Rudimentary Treatise on Masting, Mast-making, and Rigging of Ships. London: John Weale. pp. 97.
^"Lifting and Moving Equipment" (PDF). enlisted.info. United States Army. Retrieved 3 April 2014.
^John Weale (1850). Rudimentary Dictionary of Terms Used in Architecture, Civil, Architecture, Naval, etc. London: John Weale. pp. 142, 403.
^Ministry of Defence (Navy) (1995). Admiralty Manual of Seamanship. The Stationery Office. pp. 3‑192–3‑194, 3‑203. ISBN0117726966.
Further reading
R. Radcliffe (1879). "X. Sheers and Derricks". Manual of siege and garrison artillery exercises.
May 04, 2023
shear, legs, sheers, redirects, here, other, uses, sheer, also, known, sheers, shears, sheer, legs, form, legged, lifting, device, permanent, formed, solid, frame, supports, commonly, seen, land, floating, sheerleg, temporary, aboard, vessel, lacking, fixed, c. Sheers redirects here For other uses see Sheer Shear legs also known as sheers shears or sheer legs are a form of two legged lifting device Shear legs may be permanent formed of a solid A frame and supports as commonly seen on land and the floating sheerleg or temporary as aboard a vessel lacking a fixed crane or derrick Sheerlegs mounted on an M32 tank recovery vehicle When fixed they are often used for very heavy lifting as in tank recovery shipbuilding and offshore salvage operations At dockyards they hoist masts and other substantial rigging parts on board 1 They are sometimes temporarily rigged on sailboats for similar tasks Contents 1 Uses 1 1 On land 1 2 On water 2 See also 3 References 4 Further readingUses EditOn land Edit Shear legs are a lifting device related to the gin pole derrick and tripod lifting device Shears are an A frame of any kind of material such as timbers or metal the feet resting on or in the ground or on a solid surface which will not let them move and the top held in place with guy wires or guy ropes simply called guys Shear legs only need two guys whereas a gin pole needs at least three The U S Army Field Manual FM 5 125 gives detailed instruction on how to rig shears 2 On water Edit 1600 ton maximum lift capacity sheerleg Taklift 7 of Smit Internationale Fixed shear legs are most commonly found on floating cranes known as floating sheerlegs These have heavy A frame booms and vary in lifting capacity between 50 and 4 000 tons and are used principally in shipbuilding other large scale fabrication cargo management and salvage operations Temporary sheers comprise two upright spars lashed together at their heads and their feet splayed apart Unlike in a gyn which has three legs and is thus stable without support stability in sheers derricks and single legged gin poles is provided by a guy 3 The heels of the spars are secured by splay and heel tackles The point at the top of the sheers where the spars cross and are lashed together is the crutch to which a block and tackle is attached Unlike derricks sheers need no lateral support and only require either a foreguy and an aftguy or a martingale and a topping lift Being made of two spars rather than one sheers are stronger than a derrick of the same size and made of equivalent materials Unlike the apex of a gyn which is fixed the crutch of a sheers can be topped up or lowered via the topping lift through a limited angle 4 In the era of sailing vessels it was common for dockyards to employ a sheer hulk an old floating ship s hull fitted with sheer legs and used to install masts in other ships See also EditMasting sheer Sheerleg Look up shear legs in Wiktionary the free dictionary References Edit Robert Kipping 1854 Rudimentary Treatise on Masting Mast making and Rigging of Ships London John Weale pp 97 Lifting and Moving Equipment PDF enlisted info United States Army Retrieved 3 April 2014 John Weale 1850 Rudimentary Dictionary of Terms Used in Architecture Civil Architecture Naval etc London John Weale pp 142 403 Ministry of Defence Navy 1995 Admiralty Manual of Seamanship The Stationery Office pp 3 192 3 194 3 203 ISBN 0117726966 Further reading EditR Radcliffe 1879 X Sheers and Derricks Manual of siege and garrison artillery exercises Retrieved from https en wikipedia org w index php title Shear legs amp oldid 1085498588, wikipedia, wiki, book, books, library,
