A boom vang, also called a kicking strap, is a vital piece of gear on any sailboat, for safety as well as performance. On a run or broad reach, when the mainsheet traveler has been eased all the way out, further easing of the mainsheet causes the boom to rise, and puts a twist in the sail. If you trim the twisted sail to prevent the upper portion from luffing, it will be over-trimmed at the base, resulting in excess weather helm.

A vang avoids this by pulling the boom down to straighten the leech and put the head and foot of the sail more nearly in the same plane. This, in turn, reduces the amount of rudder correction needed, and improves boat speed. On a beat, a vang can be used to prevent the boom from rising whenever the mainsheet is eased for a puff of wind. Using a vang to prevent the rise and fall of the boom with every change in wind and sea conditions increases sail efficiency and gives you a steadier, more controlled ride.

When sailing downwind, vanging the boom parallel to the water's surface also limits the effect of forces pushing the top of the mast to weather, causing uncomfortable rolling or, at worst, a sudden broach. A vang can help you control jibes and prevent dangerous accidental jibes when it serves as a preventer, restraining the boom by holding it forward, not down. Properly rigged, one device can serve both functions.

A conventional vang is a block-and-tackle system attached to the boom with a strap, bail, or claw. It makes a 45° angle with the boom, and leads to an attachment point on the rail (main mast rigging chainplates are a very strong attachment point), the headsail sheet track, or a padeye installed on the cabin top or deck. On boats with short booms, where the space between the cabin top and the base of the boom is at least 25% of boom length, a compound block-and-tackle that "dead ends" at the mast and is controlled from a single point in the cockpit is very effective. Convert this rig to a combination vang/preventer by fitting the dead end with a snap shackle, so that it can be attached to several different points on the boat, and can still be adjusted from the cockpit.

Using a boom strap, which can be moved fore and aft along the boom, allows you to place the vang in the proper location for each point of sail—aft when beating, centered when reaching, and forward when running.

Rigid boom vangs are another way to control your mainsail, and a great added safety feature. A rigid vang lets you adjust sail twist when off the wind, and it can lift the boom in light air to give you more mainsail twist. It will support the boom when you're reefing or furling the main. From a safety standpoint, a rigid boom vang eliminates the topping lift, which can be extremely dangerous if it lets go. No topping lift means less wear and tear on your batten pockets, too.

There are two types of rigid boom vangs. The first is usually a rectangular housing for the purchase tackle or ratchet system. Round vangs usually have the purchase tackle mounted externally, although some telescoping tubes feature internal purchases. Support is provided by either a fixed support, a spring, or a gas cylinder.

Serious racers may prefer the more responsive coil-spring types. Cruisers with heavy displacement boats who are concerned with boom control primarily when sailing off the wind, may find the gas spring models best.

Serious racers may prefer the more responsive coil-spring types. Cruisers with heavy displacement boats who are concerned with boom control primarily when sailing off the wind, may find the gas spring models best.

Spinlock's DX index vang features a unique design which uses no spring or gas cylinder to support the boom. When the tension is off the adjusting line, the vang will maintain its height until you pull the line. With a 9:1 internal wire purchase, using a small purchase line of 3:1 on the tail gives you a powerful (24:1) vang.