Last Sunday, during the Annapolis Yacht Club Frostbite series, I watched nearly a dozen boats wipe out on the reach to the finish because they didn’t play the vang!   In a moment of hyperbole, I said to my team – “the vang is probably the most important sail control on the boat.”  OK OK OK – that might have been a bit aggressive, but I don’t think it would be too much of a stretch to say it is the most important sail control most racers rarely think about.

The vang is a sail control that was originally used to keep the boom from rising up on runs and reaches.  Through purchase, it pulls down on the boom and therefore controls leech tension or twist.  There are loads of different vang systems, but good ones are powerful and quick to adjust.  It is equally important to generate the power required to adjust highly loaded sails and to quickly ease the system to depower.  The vang needs to be in a place where it can easily be adjusted.

What do you want, when do you want it?  The vang is most often thought of as a reaching and downwind control, but it useful on all points of sail.  Downwind it is the primary twist control for the mainsail.

With the mainsheet well eased (when in doubt…) there is nothing pulling down on the boom and therefore nothing controlling the leech tension of the mainsail.  Application of vang tension creates the force needed to get the twist where we want it.  So what are we looking for?

Downwind – reaching and running – we generally shoot to create a twist profile that makes the upper batten parallel to the boom.  In other words, we have a similar angle of attack at the top of the sail that we do at the bottom.  Good indicators of this are when the top telltale is just on the verge of stalling behind the leech of the mainsail, but still flowing 90% of the time.  Vang to hard, the leech straightens out and the top telltale stalls, weather helm load increases.  Too little vang, and the top of the mainsail will begin luffing long before the bottom – making the boat underpowered, unbalanced and “wobbly.”

In light air, the boom itself often has enough “weight” to close the leech.  Because of this, we install rigid rods or springs that actually push the boom UP.  While there are very few linear relationships in sailing wind speed to vang tension is pretty close.  In light winds we generally want little or no vang tension (some boats have a rigid rod that actually pushes UP on the boom) and in heavy winds we generally want lots of vang tension.  This isn’t universally true, but a good rule of thumb.  For instance on high performance planning boats we often ease the vang in an effort of inducing twist both upwind and downwind in certain conditions.

Upwind the vang is a powerful sail trimming tool too.  On boats with bendable masts sections vang tension can have a flattening effect on the mainsail by bending the mast and therefore flattening the main.  Upwind, when you pull on the vang, the load pushes the gooseneck into the mast, and the mast bends forward.  On Lasers, J/22’s and J/24’s this is a huge depower control.  Two weeks ago at the J/Fest Southwest in Houston, Texas I watched the winning J/22 pull on enough vang to make the boom look like a banana.  The conditions were rambunctious and the rounded the first top mark of a two mile beat more than two minutes ahead of those boats that sailed with less or little vang tension.

In heavy winds, upwind we often pull on a fair amount of vang tension.  This tension limits the amount of twist that the sail can generate.  Now, on some boats (like the J/80) we want twist in the mainsail in these conditions, but we don’t want too much which can make the sail too full or quickly UNDERPOWER the mainsail when a puff hits.  Therefore vang tension allows us to ease the mainsheet and open the entire sail plan, without over-twisting the sail.

The vang receives a lot of abuse.  It is highly loaded and prone to failure.  This failure will inevitably have an impact on your performance – but could also be dangerous.  Always check the vang and its integrity before you go racing.

Try it yourself.  On the next windy day, sail upwind and when the puff hits pull on the vang and see how your boat reacts.  As the puff passes, ease the vang.  Pay special attention to the helm load and the boats heel.  On a tight reach, do the same.  Learning and remembering to play your vang in all conditions, will make you much faster.