When under sail, one of the most important important control mechanisms we have to help trim the mainsail is the vang or kicking strap (kicker).
We tend to call a line/pulley based mechanism a kicker or kicking strap and a rod or hydraulic system a vang, but the names tend to be fairly interchangeable in the sailing world, even amongst crew on the same boat!
To understand the purpose of the vang, we’ll first look at the way we adjust the mainsail. The most common trim options used by most sailors are the main sheet and the traveller. Both will adjust the angle of attack, but the main sheet is also used to change the shape of the sail. Easing the main sheet allows the boom to be let out (changing the angle of attack) and also allows it to rise in the process, thus inducing twist at the leech.
When sailing ‘off the wind’ (in other words, deeper than a beam reach), we might wish to ease the main sheet in order to ease out the sail and better present it to the wind, but if we did this without applying any vang we would see that the boom would rise and induce a huge amount of twist in the sail, depowering it.
To stop this happening, as we ease the main sheet we make sure to keep the vang firmly tight. This has the effect of keeping the boom down and retaining leach tension as the boom is eased out.
It’s important to be aware that if the vang is on too tight, for example if you’ve been beating to windward, as you bear away you should make sure to adjust the vang as necessary to avoid over tensioning the vang. There can be a lot of loads involved here and not monitoring and adjusting can cause breakages.
It’s also worth remembering that when there is significant tension on the vang, releasing it if it is running through a jammer or clutch will not be an easy process. If the weight of the vang is on a jammer, you’re going to need to transfer load to the winch first, using a winch handle.
Given that the primary reason you would want to release the vang is in order to quickly depower the mainsail, it would always be prudent to have the weight of the vang on a winch with the jammer open when sailing on a reach or deeper. Many skippers will position a crew member near the vang in such conditions on ‘vang watch’. This allows for a swift dumping of the vang in the event of a broach or round up if the helm turns to far upwind when the yacht is carrying too much sail area for that point of sail.
When sailing upwind, the vang should be ‘snugged up’ by hand and if the boat is being raced and is close to being overpowered, the vang should, once more, be kept on a winch with a crew member ready to ‘dump it’ if necessary.
Releasing the vang or tensioning up an adjustable backstay will each have a significant effect on the yacht’s handling and boat speed and will depower the sail plan, especially the mainsail.
When you are adjusting the height of the boom, for example whilst reefing, easing the vang is an important part of the process. Failing to do so will inhibit your ability to depower the main during the reefing process and will also stop the boom from rising, as it will naturally as the reefing line is tensioned.