Shear legs

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.

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.

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.

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.