A boom vang (US) or kicking strap (UK) (often shortened to "vang" or "kicker") is a line or piston system on a

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 terminology ...

used to exert downward force on the

boom Boom may refer to: Objects * Boom (containment), a temporary floating barrier used to contain an oil spill * Boom (navigational barrier), an obstacle used to control or block marine navigation * Boom (sailing), a sailboat part * Boom (windsurfin ...

and thus control the shape of the sail. The

Collins English Dictionary The ''Collins English Dictionary'' is a printed and online dictionary of English. It is published by HarperCollins in Glasgow. The edition of the dictionary in 1979 with Patrick Hanks as editor and Laurence Urdang as editorial director, wa ...

defines it as "A rope or tackle extended from the boom of a fore-and-aft mainsail to a deck fitting of a vessel when running, in order to keep the boom from riding up". The vang typically runs from the base of the

mast Mast, MAST or MASt may refer to: Engineering * Mast (sailing), a vertical spar on a sailing ship * Flagmast, a pole for flying a flag * Guyed mast, a structure supported by guy-wires * Mooring mast, a structure for docking an airship * Radio mas ...

to the

. Due to the great force necessary to change the height of the boom while a boat is under sail, a line-based boom vang usually includes some sort of a

pulley A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that ...

system. Hydraulic piston vangs are used on larger sailboats and controlled by manual or electric hydraulic pumps. By controlling leech tension, the boom vang is one way of controlling sail twist. The boom vang may also be used to flatten the mainsail on

dinghies A dinghy is a type of small boat, often carried or towed by a larger vessel for use as a tender. Utility dinghies are usually rowboats or have an outboard motor. Some are rigged for sailing but they differ from sailing dinghies, which ...

. On small sailboats and some cruising sailboats a vang may be omitted. If a vang is not installed, then the

mainsheet In sailing, a sheet is a line (rope, cable or chain) used to control the movable corner(s) ( clews) of a sail. Terminology In nautical usage the term "sheet" is applied to a line or chain attached to the lower corners of a sail for the purpos ...

has to try to control both horizontal and vertical angles of the boom. When the boom is near the centerline, the mainsheet is nearly vertical, and can exert downward force on the boom. As the mainsheet is loosened to increase the horizontal angle of the boom and sail, the mainsheet becomes horizontal and exerts less downward force. A vang works with the mainsheet to apply the downward force on the boom at all horizontal angles, allowing the mainsheet to be used to control the horizontal angle of the boom effectively. While under sail, the opposite force to the vang is supplied by the sail itself. When the sail is furled, 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 ...

supplies the upward force on the boom. Some line vang systems incorporate a piston to provide the topping lift force and to damp oscillations. Hydraulic vangs can inherently act in the topping lift role. A gnav (the word ''vang'' spelt backwards) is an inverted vang. It is a rigid strut that extends obliquely upward from the boom to the mast, exerting a force that pushes down on the boom. As the fixing point of the gnav on the boom is hauled inwards towards the mast, the downward force on the boom increases. A gnav offers more uncluttered space beneath the boom when compared to a vang.

References

{{DEFAULTSORT:Boom Vang Sailing rigs and rigging Shipbuilding Sailboat components Sailing ship components Nautical terminology he:מפרשית#בומצ'ק