Mainsail controls
1The lesson in plain words
Use the mainsail controls to set its angle, twist and depth. Change one control at a time and watch the sail.
Mainsheet and traveller
The mainsheet pulls the boom in and down. Upwind it mainly sets leech tension and twist. The traveller is a car on a track across the boat that the mainsheet runs to. It moves the boom towards or away from the centreline without changing twist much. Upwind, set twist with the sheet, then the angle with the traveller.
Kicker or vang
The kicker (UK) or vang (US) pulls the boom down. When the mainsheet is eased on a reach or run, the boom lifts and the top of the sail twists away. The kicker holds the boom down and controls twist. Upwind, the mainsheet does most of this job. Never leave the kicker so tight that the boom end can dip into the sea when rolling.
Outhaul
The outhaul pulls the clew along the boom. Tighter, it flattens the lower part of the sail, for strong wind or flat water upwind. Eased, it makes the lower part deeper, for power in light wind, in waves or off the wind. A small adjustment makes a visible change.
Cunningham
The cunningham pulls the luff down near the tack (lower forward corner), like extra halyard tension. It moves the draft forward. As the wind rises, the sail's cloth stretches and the draft moves aft; the cunningham pulls it back. Ease it in light wind; small horizontal wrinkles along the luff are acceptable then.
Backstay
On rigs designed for it, tightening the backstay bends the mast forward, flattening the main and opening its upper leech. These include many fractional rigs, where the forestay meets the mast below its top. It can also increase forestay tension; the effect depends on the rig. More backstay can therefore depower the sails. Follow the rig maker's limits: too much can damage the mast.
2Key data
- Mainsheet (upwind)
- Leech tension and twist
- Traveller
- Boom angle, with little change to twist
- Kicker / vang
- Holds the boom down; controls twist off the wind
- Outhaul
- Tight: flat lower sail. Eased: deeper, more power
- Cunningham
- Pulls the draft forward
- Backstay (bendy rig)
- Bends mast, flattens main; may reduce forestay sag
3Key points
- 1
Mainsheet sets leech tension; traveller sets the boom's angle.
- 2
Off the wind, the kicker holds the boom down and controls twist.
- 3
Outhaul tight flattens the lower sail; eased gives power.
- 4
Cunningham pulls the draft forward as the wind rises.
- 5
On a suitable bendy rig, backstay tension flattens the main and may reduce forestay sag.
4Frequent mistakes
Wrong: On a reach, ease the mainsheet and forget the kicker.
Right: Without the kicker the boom rises and the top twists away, spilling power and making the boat roll.
Wrong: Bring the boom to windward by pulling the mainsheet harder.
Right: That mostly closes the leech. Use the traveller to move the boom without over-tightening the leech.
5Practice case & exam keys
Close-hauled in 8 knots and flat water, on a rig whose mast bends under backstay tension, your mainsail is pulled very flat: outhaul hard, cunningham tight, backstay on. The boat feels sluggish after a tack.
Show the answer
The sail is too flat for light wind. Ease the outhaul to add depth in the lower sail. Ease the cunningham so the draft can move back, accepting small luff wrinkles. Ease the backstay to straighten the mast and add depth. Bring the traveller towards the centreline without over-sheeting. Keep the top leech telltale streaming most of the time while speed rebuilds; reassess trim once settled.
Exam keys
- Mainsheet: leech tension and twist; traveller: boom angle.
- Kicker/vang: holds the boom down off the wind.
- Outhaul: lower depth. Cunningham: draft position.
- Backstay on a suitable bendy rig: flattens the main and may reduce forestay sag.
Finish this unit
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