Boom vang, vang line, downhaul rope

The boom vang, in its simplest form, is a block and tackle, which is used to apply a downward force on the boom, thus preventing the boom from rising, especially when sailing downwind. If the boom vang is equipped with a support for lifting the boom, it is also referred to as a kicker or rodkicker. With such a design, you don't need a topping lift to hold the boom. Often such a kicker consists of spring-loaded telescopic tubes that support the boom from below and a tackle attached to it, with which the boom is fixed downwards.

The boom vang usually runs from an attachment point below the gooseneck at the base of the mast to a second fixed point, at about a third of the length below the boom, and from there - possibly redirected several times - back to the mast. The hauling part can be placed into the cockpit to comfortably operate the boom vang from there.

Applying the boom vang prevents the boom from rising when the mainsheet is eased and exerts little tension. This is the case on beam reaches and downwind. Here, more tension on the mainsheet would shift the angle of attack of the mainsail more towards the centreline of the ship, but would not pull the boom down. In this situation, the boom vang can hold the boom down without influencing the angle of wind attack.

Rising of the boom leads to more twisting of the sail. Applying the boom vang thus prevents or reduces this twist. The tension on the leech is increased, the sail is trimmed flatter. These trim effects of the boom vang apply equally to half-wind and upwind courses.

On dinghies, the boom vang can increase the bending of the mast. In this case, the sail profile in the lower area is additionally flattened and shifted towards the luff/mast. However, this effect cannot be achieved on larger sailing yachts with stronger rigs. Here, the backstay tensioner is usually used to adjust the mast bend.

When the boat is sailing, strong forces act on the mainsail and the boom. Accordingly, high forces are required to operate the boom vang. This is facilitated by the use of blocks with several sheaves.

The boom vang should therefore be sufficiently robust, run well over the sheaves and have a good grip. To avoid unnecessary readjustment, boat ropes for boom vangs should stretch as little as possible. High abrasion resistance reduces wear due to friction and increases the lifespan of the boom vang.

Boat ropes with Dyneema cores are particularly low-stretch. Dyneema fibres are also relatively resistant to abrasion and UV radiation. In this respect, polyester is superior, so that ropes in core-sheath construction are particularly suitable as a boom vang, either polyester double braid or Dyneema core and polyester cover.