The short version
- Sheet
- Sheet in until the boat points well and the jib's leech (back edge) sits just off the spreader or shroud — then stop. Over-sheeting is the commonest jib mistake.
- Lead
- Head up slowly and watch the windward telltales. Top lifts first: move the lead forward. Bottom lifts first: move it aft. All together: it's right.
- Halyard
- Tight enough to take out horizontal wrinkles along the luff. Tighter in a breeze, a little softer in light air.
- Slot
- The gap between jib and main. If the main's luff is bubbling, the jib is probably too tight or the slot too narrow.
A word about "wind" in this guide. Your sails, and every telltale on the boat, respond to the apparent wind — the wind you feel on a moving boat, which is stronger and further forward than the true wind upwind, and moves with every puff and lull. See true wind vs apparent wind.
On a boat with a jib, the jib sets the upwind groove. Its front edge is the first thing the wind meets, its telltales are what the helm steers by, and its back edge shapes the airflow onto the mainsail. Get the jib right and the main is half done. This guide covers upwind trim; the controls are the same on most boats, though the names and the hardware vary.
Sheet tension
The jib sheet sets how far in the sail is pulled. Close-hauled, the aim is to sheet in until the boat points well and is still fast — and no further.
- Use a reference. Most boats have a mark: the leech a set distance off the spreader tip, or the foot just touching the shroud. Mark the sheet at that setting so you can repeat it after every tack.
- Too tight chokes the sail and the slot. The boat points but feels sluggish, heels without accelerating, and the leeward telltales stall.
- Too loose and the windward telltales lift at your normal angle; the boat feels fast but can't point.
- After a tack, don't sheet in fully straight away. Leave the jib a few centimetres eased while the boat accelerates, then trim to the mark as speed builds. See how to tack faster.
Lead position
The jib lead (the car or block the sheet runs through) decides the angle the sheet pulls at. Moving it forward pulls more down on the leech; moving it aft pulls more along the foot.
| Move the lead | Leech | Foot | Twist | Use it for |
|---|---|---|---|---|
| Forward | Tighter | Fuller | Less | Light air and waves — more power |
| Aft | More open | Flatter | More | Strong wind — spill power from the top |
| Outboard, where possible | — | — | — | Footing in waves or a breeze: widens the slot |
| Inboard, where possible | — | — | — | Pointing in flat water |
The telltale test tells you where to start. Sail in the groove, then head up very slowly and watch the three windward telltales:
- All three lift at once — the lead is right for these conditions.
- The top one lifts first — the top is too open. Move the lead forward.
- The bottom one lifts first — the bottom is too closed. Move the lead aft.
Move it a hole or a few centimetres at a time, and re-test. Once you've found the right spot for each wind range, mark it. More on reading telltales in how to use telltales.
Twist
Look up the jib's leech from the foot and the top usually angles further out than the bottom. That's twist. Some is always needed, because the wind higher up is stronger and comes from slightly further aft. Too little and the top stalls; too much and the top flaps and stops driving.
You control jib twist with the lead and the sheet together. Lead forward or sheet harder: less twist. Lead aft or sheet eased: more. In a breeze, deliberately letting the top twist open — the top telltale lifting just before the others — is one of the cleanest ways to depower without losing speed.
The slot with the main
The gap between the jib's leech and the mainsail is the slot. Air leaving the jib flows over the back of the main, and the shapes of the two sails need to match.
- Main's luff bubbling or "backwinding" — a soft bulge behind the mast even with the main sheeted in — usually means the jib is too tight, or its lead too far forward or inboard, so the slot is pinched.
- A little backwinding in a breeze is often normal and doesn't cost much on many boats.
- A big, open slot — jib well eased while the main is hard in — wastes the jib's push on the main. Bring them back into step.
- In practice, trim the jib first and the main to match it, and then fine-tune both together.
Halyard and luff tension
The jib halyard (and on some boats a jib cunningham, or the rig tension itself) sets how tight the front edge of the sail is. That moves the deepest part of the sail forward or aft.
- Horizontal wrinkles running back from the luff: too little tension. Tighten.
- A vertical crease just behind the luff: too much. Ease.
- Light air: a little softer, even with small wrinkles, for a rounder front that's easier to steer.
- Strong wind: tighter, which pulls the depth forward and flattens the back of the sail so it twists open more easily.
On many boats, how much the forestay sags to leeward matters as much as halyard tension: more sag makes a fuller jib with a rounder front. That's set by rig tension and backstay, and belongs to your class tuning guide.
Settings for light, medium and heavy air
| Wind | Sheet | Lead | Halyard | Feel |
|---|---|---|---|---|
| Light | Eased a touch from your mark | Forward a little | Soft — small wrinkles are fine | Steer gently, keep the flow attached |
| Medium | On the mark | Telltales break evenly | Just wrinkle-free | Point; the narrowest groove |
| Heavy | Firm, but eased in gusts if the boat is overpowered | Aft — top opens first | Tight | Keep the boat flat; let the top spill |
| Waves | Eased slightly | Forward and outboard | As for the wind | Bear away a little for speed |
A starting point, not a recipe. Your boat's tuning guide and your own marks beat any general table.
The biggest gain for most crews isn't any one setting but repeating it: marks on the sheet, numbers by the lead track, and a crew who calls "sheet's on the mark" after every tack.
Doing it with Sail Tactician
Sail Tactician can't see your jib, but it can tell you whether a change paid.
Questions
How tight should the jib sheet be upwind?
Tight enough that the boat points well and the windward telltales stream at your normal angle, but not so tight that the leeward telltales stall or the main's luff starts bubbling. Most boats have a reference — the leech a set distance off the spreader — that you can mark on the sheet.
Where should the jib lead be?
Where all three windward telltales lift at the same moment as you head up slowly. If the top lifts first, move the lead forward; if the bottom does, move it aft.
Why is my mainsail backwinding?
Usually because the jib is sheeted too hard or its lead is too far forward or inboard, so air from the jib hits the back of the main. Ease the jib slightly or move the lead aft, and check the main is sheeted in enough.
How much jib halyard tension do I need?
Enough to remove the horizontal wrinkles along the luff — more in strong wind, less in light air. A vertical crease behind the luff means it's too tight.
Sources
Standard jib-trim practice for club racing, in general terms — class and sailmaker tuning guides give exact settings. Sail Tactician behavior from the in-app User Guide and training guide, version 3.2.
What changed
- First published.
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