On larger sailboats, the boom vang is often a combination of a shock absorber and a rope plus pulley to tighten the system as shown in this picture.

A boom vang (US) or kicking strap (UK) 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. In some cases less is more The purpose of this article is to give an overview In Sailing, a boom is a Spar (pole along the foot (bottom of a Fore and aft rigged Sail, that greatly improves control of the angle An older term is "martingale".

The vang typically runs from the base of the mast to a point about a third of the way out the boom. The mast of a sailing ship is a tall vertical or near vertical Spar, or arrangement of Spars which supports the Sails Large ships have several masts In Sailing, a boom is a Spar (pole along the foot (bottom of a Fore and aft rigged Sail, that greatly improves control of the angle 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 system. A pulley (also called a sheave or block) is a Wheel with a groove between two Flanges around its Circumference Hydraulic piston vangs are used on larger sailboats and controlled by manual or electric hydraulic pumps.

The term kicking strap is normally shortened to "kicker" whilst sailing. ie. "Hard on the kicker when we get to the leeward mark"

On some sailing boats, such as the 49er, rather than a set of lines pulling the boom downwards, a rigid member is used to push the boom down. The 49er is a newer One-design class of small sailing dinghy. As this is the reverse of a vang, it is known as a "gnav".

By controlling leech tension, the boom vang is one of the three methods of controlling sail twist. Sail twist is a phenomenon in Sailing where the head of the Sail is at a different Angle of attack from the foot of the sail in order to change the

On small sailboats and some cruising sailboats a vang may be omitted. If a vang is not installed, then the sheet has to try to control both horizontal and vertical angles of the boom. In Sailing, a sheet is a line ( Rope, Cable or Chain) used to control the moveable corner(s of a Sail. When the boom is near the centerline, the sheet is nearly vertical, and can exert downward force on the boom. As the sheet is loosened to increase the horizontal angle of the boom and sail, the sheet becomes horizontal and exerts less downward force. A vang works with the sheet to apply the downward force on the boom at all horizontal angles, allowing the sheet 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 supplies the upward force on the boom. The topping lift (more rarely known as an uphaul) is a line which is part of the rigging on a Sailboat; it applies upward force on a Spar 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.