Sheers.
1. (Nautical.) Originally spelt shears, from the resemblance, in form, to cutting shears. Bailey, 1725; Phillips' “World of words,” 1658. Modern maritime custom has otherwise determined it. An apparatus consisting of two masts, or legs, secured together at the top, and provided with ropes or chains and pulleys; used principally for masting or dismantling ships, hoisting in and taking out boilers, etc. This kind of hoisting-machine has two legs. The derrick has one; the gin, three. The two former require guys; the latter stands independently. The legs are separated at their feet to form an extended base, and are lashed together at their upper ends, to which the guy-ropes and tackle are attached. The sheers has one motion on its steps describing an are, and is inclined from the perpendicular to a greater or less extent as required, by slacking or hauling on the guy-rope or fall of the sheertackle. Temporary sheers are made of two spars lashed together at top and sustained by guys. Permanent sheers are sloped together at top and crowned with an iron cap bolted thereto. It is now usually mounted on a wharf, but was formerly placed on an old hull called a shear-hulk, The sheers of Sheerness Dockyard, England (Fig. 4954), are 127 feet long, with an average diameter of 37 inches, and framed like a lower mast of a first-rate. In Fig. 4955, A represents Wylie's sheers. a a shows the sheers overhanging a vessel b b, in position for raising or lowering an object on the wharf, c, the two engines d, a long screw for working the sheers, e, hoisting-winch with wormed barrel. f f, purchase-blocks. B, the sheers at Woolwich Dockyard, end and side elevation. The spars b c and central mast a are made, the pieces being joined by dowel-pins and iron plates. They are connected with each other by straps d and with the mast by braces e, and the spars c are swiveled on a collar at the foot of the central mast. A similar contrivance is used in mining and for suspending the tackle used in mounting and dismounting guns. [2142]
