Boom vang

A boom vang (US) or kicking strap (UK) (often shortened to "vang" or "kicker") is a line or piston system on a sailboat used to exert downward force on the boom and thus control the shape of the sail.

If a vang is not installed, then the mainsheet has to try to control both horizontal and vertical angles of the boom.

When the sail is furled, a topping lift supplies the upward force on the boom.

Some line vang systems incorporate a piston to provide the topping lift force and to damp oscillations.

A gnav offers more uncluttered space beneath the boom when compared to a vang.

On larger sailboats, the boom vang is often a combination of a spring-loaded telescopic tube to support the boom and a pulley system to tighten the vang as shown in this picture.