Boom Vang / Kicker: Trimming the Boom Purchase

The vang, or kicker, is the purchase that links the boom to the base of the mast, and its whole job is to control boom height and therefore the tension in the mainsail leech, especially once the traveller and mainsheet can no longer hold the boom down for you. Pull it on and you drag the boom downward, close the leech and load the sail with power; ease it and the leech opens, the top of the sail spills wind and the boat depowers and stands upright. Learning to dose it properly changes how your mainsail performs on every point of sail, not just upwind, and it is one of the cheapest, fastest gains available to any cruiser or racer who has never really used it.

What the vang is and how it works

The vang is a purchase system, usually multi-part and sometimes assisted by a gas spring or a rigid strut, tensioned between a low fitting on the mast and a fitting on the underside of the boom a short distance aft of the gooseneck. Because it is anchored low on the mast and pulls on a point close to the mast, it exerts a strong downward and slightly forward pull on the boom regardless of where the boom is swung out to. That single downward pull produces two linked effects that sit at the heart of mainsail trim: it increases the tension along the leech, which is the trailing edge of the mainsail, and it reduces twist, the progressive change in angle between the lower panels of the sail and the upper panels near the head. Everything the vang does for you flows from those two consequences, so it pays to think of the control not as a rope you tension but as a dial for leech tension and twist.

Why the mainsheet is not enough

Upwind, with the boom close to the centreline, the mainsheet pulls the boom almost straight down, so most of your leech control comes from the sheet and the traveller working together. The moment you bear away, though, the geometry changes against you. As the boom swings outboard the mainsheet lead becomes more and more horizontal, so the same amount of sheet tension increasingly pulls the boom inboard rather than down. Past a beam reach the sheet has almost no downward component left at all, and if that were your only control the boom would rise, the leech would fall open and the top of the sail would sag off to leeward and stop working. The vang solves this because its geometry does not change: anchored at the base of the mast, it keeps pulling the boom down whether the boom is on the centreline or squared right out to the shroud. That is the core reason the vang exists, and it is why the control earns its keep off the wind far more than on it.

Leech and twist: what you are actually trimming

To trim the vang with intent rather than by feel alone, it helps to picture the mainsail as a stack of horizontal profiles running from the foot up to the head, each one an aerofoil section presenting itself to the wind. When the boom is free to rise, the upper sections rotate open and spill their wind to leeward, so the head of the sail is working at a much flatter angle than the foot: this is twist. A degree of twist is not a fault to be eliminated, it is a tuning tool. In strong wind and in gusts you actively want some twist so the top of the sail bleeds off pressure, keeps the boat on its feet and reduces the heeling moment high up where it hurts most. In steady medium air, by contrast, too much twist is simply power left on the table, because the head of the sail is feathering when it could be driving. The vang is your primary means of setting how much twist you carry, and reading the leech telltales, especially the top one, tells you whether you have it right.

On versus off, in plain terms

• Vang on: boom pulled low, leech tensioned and closed, little twist, more power and more heel. This is what you want when you are underpowered and hunting for drive, or reaching in flat water.
• Vang off: boom rises, leech opens, twist increases, the sail depowers, the boat sits more upright. This is your fast response to being overpowered, to a building breeze or to a puff that lays the boat over.

The vang never works in isolation. It is one instrument in the wider orchestra of running rigging, alongside the mainsheet, traveller, halyards, outhaul, cunningham and backstay, and every one of those controls changes the shape the vang is acting on. If you want the full picture of how these lines interact and how to choose them for your boat, our guide to choosing running rigging lays out the whole system so the vang settings below make sense in context.

How to trim the vang on each point of sail

There is no single correct vang tension, only the tension that suits the point of sail, the wind strength and the sea state you are in at that moment. The settings below are a framework to work from, and the fastest way to internalise them is to make a change, watch the top leech telltale and feel the helm, then adjust again. What follows walks around the compass from close-hauled to dead downwind, then treats the special case of heavy air where the vang becomes a rapid depowering tool.

Upwind and close-hauled

Sailing to windward the mainsheet and traveller do almost all of the leech work, so the vang should be kept soft, just snug enough to take up the slack without loading the boom. Its role here is mainly insurance: a lightly tensioned vang stops the boom flying dangerously upward if you are caught by an accidental gybe or a sudden broach, but it should not fight the traveller and sheet for control of the leech. If you pull the vang on hard upwind you effectively lock the boom height and rob the mainsheet of its ability to fine-tune twist through the tack, which makes the boat harder to keep in the groove. In lighter airs you may want the vang genuinely slack so the leech can breathe, while as the breeze builds you can pre-tension it a little so that when you bear away at the windward mark the transition is quicker.

Reaching and broad reaching

This is where the vang earns its reputation, because as you crack the sheet and bear away the boom swings out and the mainsheet loses its downward grip almost entirely. Without the vang the leech would fall open, the top of the sail would twist off and the mainsail would lose a surprising amount of drive right when you are trying to make the most of a fast, powered-up point of sail. Pull the vang on to bring the leech back to the tension it had upwind, close down the excess twist and get the whole sail driving again. Aim to set it so the top leech telltale flows most of the time and just occasionally curls behind the sail, which tells you the leech is loaded but not stalled. Of all the points of sail, this is where a correctly tensioned vang makes the single biggest difference to boat speed, and it is also the setting most cruisers forget to make.

Running dead downwind

Running with the wind aft, the mainsheet is fully eased and the boom is squared right out, so the vang is essentially your only control over mainsail twist. Pulling it on flattens the leech profile and, just as usefully, keeps the boom steadier and lower, which reduces the chance of the leech folding forward and triggering a dangerous accidental gybe. There is an important limit, though. In a building sea with the boat rolling, an over-tight vang holds the boom rigidly down, and on a deep roll to leeward the boom end can catch the water, which slams load into the gooseneck and the rig and can round the boat up hard or even trip it. The seamanlike compromise downwind in waves is a vang firm enough to control twist and steady the boom but eased enough that the boom can lift clear if a wave rolls under you. Judge it by watching the boom through a few rolls before you commit to a setting.

Strong wind, gusts and the "gear change"

Heavy air is where the vang shows its second personality, as a fast, one-handed depowering tool. When a gust hits while you are hard on the wind, dumping the vang instantly opens the leech, spills the top third of the sail and stands the boat back onto her feet, all without touching the mainsheet or moving the traveller. Because you can throw it off and grind it back on quickly, experienced crews treat the vang as a gear lever: on for the lulls to keep the sail powered, off for the puffs to shed heel and keep the rudder from stalling. This technique, often called vang sheeting, lets the helm hold a steadier course and a lighter, more balanced tiller through gusty conditions, and it saves an enormous amount of exhausting mainsheet work over a long beat. In really strong wind, sailing with the vang a touch eased as your baseline and using the sheet only for fine trim is a proven, low-effort way to keep control.

Table: what the vang does

Types of vang: purchase, rigid and hydraulic

Not every vang is built the same way, and the type fitted to your boat changes both what the control can do and how you should look after it. Understanding the differences helps you decide whether an upgrade is worth it and how to trim what you already have.

Simple purchase (cascade or block-and-tackle) vang

The classic vang is a straightforward block-and-tackle, often a cascade of two purchases stacked to multiply power, running from a mast fitting to the boom with a tail led to a cam cleat. It is light, cheap, reliable and easy to service, and it does the one job of pulling the boom down extremely well. Its limitation is that it can only pull, never push: when you drop the mainsail the boom is unsupported and will fall into the cockpit unless you rig a topping lift or a boom crutch to hold it up. For many cruising boats that trade-off is perfectly acceptable, and a well-specified purchase vang with a generous mechanical advantage gives you all the leech control you need at a fraction of the cost of the alternatives.

Rigid (solid) vang with strut or spring

A rigid vang, sometimes called a solid or boom kicker, replaces the lower part of the tackle with a telescopic strut containing a gas spring or a coil spring. It still pulls the boom down under load exactly like a purchase vang, but because it is rigid and sprung it also holds the boom up when the sail is lowered or reefed, which does away with the topping lift entirely and makes reefing and sail stowage far tidier. The spring supports the weight of the boom and mainsail so the sail flakes cleanly onto the boom, and there is no flapping topping lift to chafe the leech. The trade-offs are more weight aloft, higher cost and a few more moving parts to maintain, but for a shorthanded cruiser the convenience of never rigging a topping lift again is often decisive.

Hydraulic vang

On larger yachts and performance boats the vang may be hydraulic, driven by a pump so the crew can apply and release very high loads precisely and repeatably. Hydraulics give fine, powerful control and hold their setting rock solid, but they are heavier, more expensive and demand proper maintenance of seals and fluid. Most owners of production cruisers and small racers will never need one, and the choice between a purchase vang and a rigid vang is the practical decision that matters for the majority of boats.

Rigging and hardware: making the purchase work

A vang is only as good as the hardware it runs on, and a control that is too stiff to adjust under load is a control you will simply stop using. The purchase ratio is the first thing to get right: the vang works at a shallow angle to the boom, which is mechanically inefficient, so it needs a high purchase, commonly around eight-to-one or more on a mid-size cruiser, to let one person tension it while the sail is loaded up. Beyond the ratio, the quality and free-running of the blocks matters enormously, and this is where low-friction hardware pays off. Modern low-friction rings and good-quality sheaves reduce the drag inside the cascade so more of the effort you put in actually reaches the boom, making the whole system quicker and lighter to trim. The line itself should be a low-stretch, hard-wearing cover that grips a cam cleat well and is kind to your hands, and the lead to the cleat should be fair so the tail releases cleanly when you dump it in a gust.

Where the loads go

It is worth remembering that the vang imposes significant compression on the boom and a strong downward and forward load on the mast fitting, so both the boom and its fittings need to be strong enough for the purchase you fit. On boats where the vang is used aggressively as a primary control, the gooseneck and the vang tang see real cyclic loading, which is one more reason to inspect these fittings regularly rather than assuming a mainsail control is a low-stress part of the rig.

Common mistakes and how to avoid them

The most frequent error, by a wide margin, is simply never touching the vang at all off the wind, leaving the leech to fall open on every reach and run and quietly giving away speed the whole time. The opposite fault is over-tensioning: too much vang upwind hooks the leech to windward, which stalls the top of the sail, adds weather helm and actually slows the boat, while too much vang running in a seaway invites the boom to catch the water on a roll. A third mistake is forgetting to ease the vang before you gybe or before you drop the main, because a hard-loaded vang makes the boom swing violently through a gybe and leaves the boom pinned down when you want it supported for stowage. The cure for all three is the same simple habit: treat the vang as an active control you adjust every time the point of sail or the wind strength changes, watch the top leech telltale as your feedback, and always know which way you last set it. Building that habit, together with tidy sail handling systems such as well-set lazy jacks, turns the vang from a rope you ignore into one of the most useful controls on the boat.

Maintaining the purchase

An effective vang has to run freely, because a purchase that binds under load will not let you make the quick, decisive adjustments that make the control worth having in the first place. Keep the blocks clean and rinsed of salt, check the line for chafe and glazing where it turns through the sheaves, and confirm that the cam cleat still grips without slipping and releases cleanly under load. If you find the vang has become hard to pull, resist the temptation to blame the wind strength and instead inspect the sheaves for a seized bearing, the line for swelling or a hard spot, and the lead for a fouled turn, because a stiff purchase almost always has a mechanical cause you can fix. On a rigid or hydraulic vang, follow the maker's schedule for the gas strut or the seals and fluid, since a spring that has lost its gas will no longer support the boom and a leaking hydraulic ram will not hold its setting. A few minutes of attention each season keeps the vang doing its job quietly and reliably for years.

Frequently asked questions

What is the difference between a vang and a kicker?

There is no difference of substance between the two. "Vang", or more fully "boom vang", is the term used most in North America, while "kicker", short for "kicking strap", is the traditional British and European name for exactly the same piece of equipment. Both words describe the purchase that pulls the boom downward to control leech tension and twist. If a crew talks about the kicker and another about the vang, they are talking about the identical control, and the trimming advice for one applies word for word to the other.

Is the vang only useful for racing?

Not at all, and the belief that it is racing-only is exactly why so many cruisers underuse it. On a cruising boat a well-set vang gives you noticeably better performance on every reach and run, which shortens passages, and it gives you a fast, low-effort way to depower in a gust, which makes the boat safer and more comfortable when the breeze pipes up. It also steadies the boom downwind, reducing the risk of a violent accidental gybe. For the effort of learning one control, the vang is one of the best returns on a cruising boat, and it is genuinely among the most useful and least-used lines aboard.

Rigid vang or simple purchase: which should I choose?

It depends on how you sail and what you value. A simple purchase vang is lighter, cheaper and easier to maintain, and it controls the leech every bit as well as a rigid vang, but it cannot hold the boom up when the sail is down, so you still need a topping lift or a boom crutch. A rigid vang with a strut or gas spring does everything the purchase vang does and also supports the boom when you reef or lower the main, which removes the topping lift and makes shorthanded sail handling much tidier, at the cost of more weight aloft and a higher price. For a performance-minded owner who is happy with a topping lift, a good purchase vang is fine; for a cruiser who prizes easy reefing and stowage, the rigid vang usually wins.

Can I use the vang instead of the mainsheet?

No, because they are complementary controls rather than substitutes, and the boat needs both. Upwind the mainsheet is in charge of the leech and the vang stays soft; as you bear away and the sheet loses its downward pull, the vang takes over leech and twist control. The mainsheet also controls the boom's angle to the centreline, which the vang cannot do at all. The right mental model is that the mainsheet and vang share responsibility for the same leech, handing off to each other as the point of sail changes, so you trim them as a pair rather than choosing one over the other.

How tight should the vang be upwind?

Upwind you want the vang only just snug, taking up the slack without loading the boom, so that the mainsheet and traveller retain full control of leech tension and twist through the tack. In light air you can leave it genuinely soft so the leech breathes and the top telltale flows freely; as the wind builds you can pre-tension it a little so the transition is quicker when you bear away. The key is to avoid pulling it on hard on the wind, because a heavily loaded vang upwind hooks the leech, stalls the head of the sail and adds weather helm, all of which slow the boat rather than speed it up.

Why does easing the vang help in a gust?

Easing the vang in a gust works because it instantly opens the leech and lets the upper part of the mainsail twist off and spill wind. Since the top of the sail generates a large share of the heeling force, high up where it has the most leverage, dumping that pressure stands the boat back upright, lightens the helm and stops the rudder from stalling, all without touching the mainsheet or the traveller. Because you can release and re-tension the vang quickly, crews use it as a gear change through gusty conditions, easing for the puffs and pulling back on for the lulls, which keeps the boat balanced and the course steady with far less effort than working the mainsheet for every gust.

Bringing it together

The vang rewards a simple shift in mindset: stop thinking of it as a rope that lives in a cleat and start treating it as a live dial for leech tension and twist that you adjust every time the point of sail or the wind changes. Keep it soft upwind and let the mainsheet lead, pull it on as you bear away so the reach and run stay powered, ease it in the gusts to depower fast, and mind the boom in a downwind seaway so it never dips the water. Back that trimming habit with free-running blocks, a sensible purchase ratio and a bit of seasonal maintenance, and the vang becomes one of the most rewarding controls on the boat. If you are setting up or refining your deck systems, it is worth reading it alongside our wider guides to running rigging and looking at how quality hardware such as the Olli Flex block range can make every control on board quicker, lighter and more precise to use.