Our continuing saga in the quest for more speed leads us to the center of the boat to an often-known, but sometimes under-utilized little guy: The Boom Vang. I’ll break our discussion into two parts. First, the pieces-parts of the vang system, second, the use of the vang. Once again our focus is to make sailing the boat easier. This usually means making the rigging easier or more convenient to adjust. By making the vang one of these easy systems we can gain boat speed upwind in heavy air and downwind in all conditions.
The easiest way to get the crew to use the vang is to make it accessible. A worn-out plastic clam cleat on top of the thwart is not an easily adjusted system. A 360° swivel with a cam cleat on the trunk or a double-ended system led up to the side decks or the coaming are two accessible layouts. My personal preference is the 360° swivel on the trunk. This location allows adjustment from any position in the boat. The cleat follows the user. I have the middle crew adjust the vang upwind and either the forward crew or I adjust it downwind depending on the wind conditions. I recommend a 12 to 1 system to start. You can increase or decrease the power ratio depending on the primary user on your boat. You want the vang to be powerful enough to bend the mast in heavy air, but not so powerful that an over-anxious crew snaps the boom in two.
As shown in the main figure, two Harken single Bullet blocks are rigged in a cascade arrangement between the wooden stanchions and the boom. The upper block is located about two feet from the boom on a 1/8″ wire strop (or a piece of 1/4″ Spectra line). Make sure to check the wire strop for broken strands before every regatta. Use a very low stretch line (Spectra) in at least these two cascades from the boom (these have the highest loads). A Harken swivel Bullet block with a becket is mounted on the port stanchion with a through-bolted bail. The other end of the line from the first block passes through a hole (minimum 2″ from the edge) in the starboard stanchion and is knotted with a double overhand stopper knot. The line from the 360° swivel turns through a cheek block screwed to the trunk directly beneath the swivel and goes forward to a single Bullet block with a becket, then back to another cheek under the thwart then back to the becket. Make sure to leave enough lines in this last part so that the Bullet w/ becket can travel the entire distance between the cheek block on the trunk and the block on the stanchion. This is to ensure plenty of travel for the vang. We don’t want to be able to say “if only the vang had a little more slack” after the capsize.
The detailed figure shows a possible double-ended system led to both side decks. With this system, the goal is to keep most of the working pulleys (the power ratio portion of the system) either in between the stanchions and the boom or between the bow and the boom. If you have two identical 3-to-1 systems under each deck pulling on one 4 to 1 system at the stanchions you run the risk of bottoming out one of the individual 3-to-1s before you have the vang set as tight as you want it. The opposite can happen with almost any double-ended system. You must have long enough tails on the lines to ensure that you don’t run out of line trying to ease the vang in a wicked puff. If the pulling and cleating portion of the line (the part you play with while sailing) is continuous from one side to the other, these limits can be widened. My only real gripe with the double-ended vangs is that it is a hassle to ease and trim them when sitting down in the cockpit.
Regardless of how you decide to rig your vang, make sure to use low stretch line, at least Bullet-sized blocks, beefy bails on the boom and the stanchions, and through-bolt everything you can.
Using the vang is not one of the lost rituals of any jungle sailor tribes. It is simply knowing when and how much to use.
The cardinal rule of vanging is to keep the upper batten on the main parallel to the boom. You have probably heard this a zillion times. If you follow only this rule you’ll be set 99% of the time. To set the upper batten parallel, look up at the top batten while sitting directly under the boom. The batten should be in line with the boom. This will ensure that the top of the sail is working the way it should. Play with the vang while you watch the batten. See what happens when you crank it on in light air (it points windward as the leech stands up) or release it completely in a blow (it will fall way off as the leech twists off to leeward). This is mostly used while reaching or running when the mainsheet isn’t pulling down on the boom anymore. For upwind work, the vang is used to de-power the main by bending the mast and flattening the main when you can’t keep the boat flat with just the traveler. Ideally, you can get enough vang tension so that the boom won’t rise if you ease the mainsheet in a big-stinkin’ puff. This is called vang-sheeting. Still, don’t pull so hard that the upper batten points too windward. The vang should not be a set-it-and-forget-it control. The more you use it, the more you’ll gain.
I hope this covered the basics. The last rule: 1) Be careful with wooden booms and masts. They will break if you wail on the vang. 2) Make sure you ease the vang before you round the windward mark. Even aluminum booms and masts can break. Good luck!