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 An A-frame is a basic structure designed to bear a load in a lightweight economical manner. The simplest form of an A-frame is two similarly sized beams, arranged in an angle of 45 degrees or less, attached at the top, like an uppercase lette ...

and supports, as commonly seen on land and the

floating sheerleg A floating sheerleg (also: shearleg) is a floating water vessel with a crane built on shear legs. Unlike other types of crane vessel, it is not capable of rotating its crane independently of its hull. There is a huge variety in sheerleg capaci ...

, or temporary, as aboard a vessel lacking a fixed crane or derrick. When fixed, they are often used for very heavy lifting, as in tank recovery, shipbuilding, and offshore salvage operations. At

dockyard A shipyard, also called a dockyard or boatyard, is a place where ships are built and repaired. These can be yachts, military vessels, cruise liners or other cargo or passenger ships. Dockyards are sometimes more associated with maintenance ...

s they hoist masts and other substantial rigging parts on board. They are sometimes temporarily rigged on

sailboat A sailboat or sailing boat is a boat propelled partly or entirely by sails and is smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region and maritime culture. Types Although sailboat terminolo ...

s for similar tasks.

Uses

On land

Shear legs are a lifting device related to the

gin pole A gin pole is a supported pole that uses a pulley or block and tackle on its upper end to lift loads. The lower end is braced or set in a shallow hole and positioned so the upper end lies above the object to be lifted. The pole (also known as ...

derrick 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 ...

and tripod (lifting device). Shears are an

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-wire A guy-wire, guy-line, guy-rope, or stay, also called simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly for ship masts, radio masts, wind turbines, utility poles, and tents. A ...

s 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.

On water

Fixed shear legs are most commonly found on floating cranes known as

s. 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 A gyn is an improvised three legged lifting device used on sailing ships. It provides more stability than a derrick or sheers, and requires no rigging for support. Without additional support, however, it can only be used for lifting things dire ...

, which has three legs and is thus stable without support, stability in sheers (derricks, and single-legged gin poles) is provided by a guy. 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 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 on ...

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 The topping lift (more rarely known as an uphaul) is a line which applies upward force on a boom on a sailboat. Part of the running rigging, topping lifts are primarily used to hold a boom up when the sail is lowered. This line would run from nea ...

. 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. In the era of sailing vessels, it was common for dockyards to employ a

sheer hulk A hulk is a ship that is afloat, but incapable of going to sea. Hulk may be used to describe a ship that has been launched but not completed, an abandoned wreck or shell, or to refer to an old ship that has had its rigging or internal equipment ...

, an old floating ship's hull fitted with sheer legs, and used to install masts in other ships.

Uses

On land

On water

See also

References

Further reading