Guy line

A guy-wire, guy-line, guy-rope or guide-wire, also known as simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly in ship masts, radio masts, wind turbines, utility poles, fire service extension ladders used in church raises and tents. A thin vertical mast supported by guy wires is called a guyed mast. Structures that support antennas are frequently of a lattice construction and are called "towers". One end of the guy is attached to the structure, and the other is anchored to the ground at some distance from the mast or tower base. The tension in the diagonal guy-wire, combined with the compression and buckling strength of the structure, allows the structure to withstand lateral loads such as wind or the weight of cantilevered structures. They are installed radially, usually at equal angles about the structure, in trios and quads. As the tower leans a bit due to the wind force, the increased guy tension is resolved into a compression force in the tower or mast and a lateral force that resists the wind load. For example, antenna masts are often held up by three guy-wires at 120° angles. Structures with predictable lateral loads, such as electrical utility poles, may require only a single guy-wire to offset the lateral pull of the electrical wires, at a spot where the wires change direction.

Conductive guy cables for radio antenna masts may disturb the radiation pattern of the antenna, so their electrical characteristics must be included in the design.

The guys supporting a sailboat mast are called "standing rigging" and in modern boats are stainless steel wire rope. Guys are rigged to the bow and stern, usually as a single guy. Lateral guys attach to "chain plates" port and starboard attached to the hull. Multiple guys are usually installed with spreaders to help keep the mast straight ("in column"). Temporary guys are also used on a sailboat, a fore-guy is a term for a line (rope) attached to and intended to control the free end of a spar. On a modern sloop-rigged sailboat with a symmetric spinnaker, the spinnaker pole is the spar most commonly controlled by one or more guys.

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