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Vangs prevent the boom from rising, which tensions the leech of the sail, and in turn removes twist from the mainsail. By removing the twist and flattening the sail, stability improves in a seaway, reducing roll and rudder correction, speed increases and the boat is able to sail closer to the wind.
There are two types of boom vangs: block and tackle vangs, and solid vangs. The forces which operate on vangs are focused under the mainsails center of effort. That center of effort is the best location of attachment to the boom however, it changes on different points of sail. It moves forward running downwind, is centered when reaching and moves farther aft when close-hauled.
BLOCK & TACKLE VANGS
- The basic system has a 3:1 or 4:1 purchase using a fiddle block for attachment to the boom and a fiddle block with becket and cam cleat for attachment to the mast.
- The boom fiddle block should be fitted with a snap shackle or detachable becket for removal from the boom if a boom strap is not used.
- To increase purchase to 6:1 or 8:1, add a doubling block at the boom fitting.
- Self-cleating vangs are generally used on small dinghies. A small block is used on the boom and a fiddle with V-jam or cam cleat is attached to the mast base.
- If the vang is to be used as a preventer, the mast end block should also be fitted with a snap shackle. The block and tackle vang, by adding a snap shackle at the dead end and relocating the point of attachment, can be used as a preventer permitting a controlled jibe, and for running downwind by holding the boom forward, rather than down.
- The blocks and tackle are fitted to the boom by either a strap, or a long, deep-V bail, or vang bracket.
- The solid vang eliminates the need for a topping lift.
- Solid vangs should have an adjustable tensioning device, which can be set to receive the desired angle.
- Purchase systems on solid vangs can be coil-spring type, gas spring, ratchet, and tackle.
CHOOSING A BOOM VANG AND FITTINGS
There are a few factors to consider in selecting a vang:
- Decide whether a solid vang or a block and tackle vang is desirable keeping in mind that the primary advantage to a solid vang is the elimination of the topping lift.
- Determine if the vang will be controlled by the crew, or by the skipper from the cockpit.
- Appraise what amount of mechanical advantage is required for controlling the mainsail.
- Small dinghies require no more than 3:1 purchase.
- Larger dinghies and small keelboats use 4:1 or 5:1.
- Larger boats may need 8:1 purchase or more.
- Always use the manufacturers recommendations in the selection of a vang for your particular boat and sailing style, whether racing, cruising or daysailing.
- Fittings should be matched to the vang. There is no sense paying the additional cost of fittings meant for solid vangs if a block and tackle vang is going to be used. Whichever fitting is used on the boom, it must be able to distribute loads over a wide area.
The average-skilled person with minimal tools can install a boom vang.
- Drill and bits
- Fasteners, if a block and tackle vang kit or solid vang is used
- Splicing tool, line, and blocks for non-kit block and tackle vangs