Shear legs

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For other uses, see Sheer.
Sheerlegs mounted on tank recovery vehicle

Sheers (Shears, Sheer legs, or Shear legs) are a form of two-legged lifting device, that were used by sailboats and dockyards for tasks such as lifting masts and heavier parts of the rigging on board.[1]

Nautical[edit]

Unlike in a gyn, which has three legs and is thus stable without support, stability in sheers (and in a derrick) is provided by a guy.[2] Sheers comprise two upright spars, lashed together at their heads and their feet splayed apart. 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.[3]

On land[edit]

Shear legs or simply "shears" 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 where a gin pole needs at least three guys. The U. S. Army Field Manual FM 5-125 gives detailed instruction on how to rig shears.[4]

See also[edit]

References[edit]

  1. ^ Robert Kipping (1854). Rudimentary Treatise on Masting, Mast-making, and Rigging of Ships. London: John Weale. p. 97. 
  2. ^ John Weale (1850). Rudimentary Dictionary of Terms Used in Architecture, Civil, Architecture, Naval, etc. London: John Weale. pp. 142,403. 
  3. ^ Ministry of Defence (Navy) (1995). Admiralty Manual of Seamanship. The Stationery Office. pp. 3‑192–3‑194, 3‑203. ISBN 0117726966. 
  4. ^ "Lifting and Moving Equipment". enlisted.info. United States Army. Retrieved 3 April 2014. 

Further reading[edit]

  • R. Radcliffe (1879). "X. Sheers and Derricks". Manual of siege and garrison artillery exercises.