The short version
- What they are
- Short strips of yarn or ribbon on the sails that show how the air is flowing over each side. Streaming aft means the flow is smooth. Lifting, spinning or drooping means it isn't.
- Jib luff telltales
- Windward one lifting: you're too close to the wind — bear away, or sheet in. Leeward one stalling: you're too far off — head up, or ease.
- Main leech telltales
- Show whether the back of the mainsail is too tight or too open. A stalled top telltale usually means ease the sheet or vang a little.
- Steer or trim?
- Steer for a passing gust, wave or flicker. Trim when the same pattern sticks around.
What telltales are and where they go
A telltale is a light strip — wool, nylon ribbon or a cassette-tape-like film — stuck to a sail so it can move freely. When air flows smoothly past it, it streams straight back. When the flow breaks down, it lifts, spins, droops or curls. That's all it does, and it's the most useful few grams on the boat.
- Jib (or genoa) luff telltales sit a hand's width or so back from the front edge of the sail, in pairs — one on each side — usually at three heights. A window in the sail or a translucent cloth lets you see the far one. These are the ones you steer by.
- Mainsail leech telltales are attached to the back edge of the main, usually at the batten pockets. These tell you about mainsail trim, not steering.
- Some mainsails also have luff telltales near the mast. They're harder to read because the mast disturbs the flow, and many sailors ignore them.
What we use on the sails: Davis Instruments Air-Flow Tels — light nylon telltales that react in the lightest air and come with their own adhesive patches. And a useful trick: spray a little McLube Sailkote on the sail where each telltale sits, both sides. It leaves a dry, slippery film, so a telltale that gets wet or static-charged slides free instead of sticking flat to the cloth.
On a boat with only one sail, such as a Laser/ILCA or an Optimist, there's no jib, so the main's luff telltales do the jib's job — see trimming a single-sail boat.
Reading the jib's luff telltales
The windward telltale is on the side of the sail the wind hits first. The leeward one is on the other side, the one you usually see through the window. Sailing close-hauled, there are three patterns to know:
| What you see | What it means | Steer | Or trim |
|---|---|---|---|
| Both streaming aft | Smooth flow on both sides | Hold your course | — |
| Windward lifting or spinning | Too close to the wind (or sail too loose) | Bear away | Sheet in |
| Leeward drooping or curling | Too far off the wind (or sail too tight) — the sail has stalled | Head up | Ease |
| Both misbehaving | Trim is wrong, or the wind is too light to read | — | Check sheet and lead |
On a tiller boat there's a memory aid that works on either tack: push or pull the tiller toward the telltale that's misbehaving. Windward telltale lifting? Tiller toward the windward side, which bears you away. Leeward stalling? Tiller toward leeward, which heads you up. With a wheel it's the other way round: turn the bow away from the misbehaving telltale.
A stalled leeward telltale is the worse of the two. A lifting windward telltale means you're a little high and losing a bit of power; a stalled leeward one means the flow has broken away from the back of the sail and you've lost far more. When in doubt, err on the side of keeping the leeward telltales streaming.
Steer or trim?
Both fixes work, and choosing between them is a matter of time:
- A flicker that comes and goes — a wave knocking the bow, a short gust — is a steering job. Correct it with the helm, then come back.
- A pattern that lasts — the windward telltale lifting every time you sail your normal angle — is a trim job. The wind has changed strength, or the sheet has slipped. Fix the sail so that your fastest angle gives you streaming telltales again.
- Steady but on a new heading — everything streams, but the compass has moved several degrees — is a wind shift. That's a tactics job: see playing the shifts.
Close-hauled, a common setup is to trim the jib for your best angle and then steer to the telltales with the sheet left alone. Many fast sailors like the windward telltale to flick up occasionally — a sign they're right at the top of the groove rather than comfortably below it.
Top, middle and bottom
With three pairs of telltales up the luff, you can also check whether the sail is set evenly. Sail in the groove and head up very slowly, watching which windward telltale lifts first:
- All three lift together: the sail is set evenly from top to bottom. Leave it.
- The top one lifts first: the top of the sail is too open (too much twist). On most boats, move the jib lead forward or sheet a little harder.
- The bottom one lifts first: the bottom is too tight relative to the top. Move the lead aft.
In a breeze, letting the top go first — a little extra twist — is often deliberate, because it spills power from up high where it heels the boat most. The details are in how to trim the jib.
Mainsail leech telltales
Leech telltales stream off the back of the mainsail when air leaves it cleanly. When the back of the sail is pulled too tight, the air can't leave cleanly; the telltale curls round behind the sail and disappears from view. That's a stall.
- The top telltale is the one to watch. In medium air, aim for it to be streaming most of the time and folding behind the sail now and then.
- It never streams: the leech is too tight. Ease the mainsheet a little, or the vang (kicker) if you have one.
- It streams all the time and the boat feels underpowered: the leech may be too open. Sheet in a little.
- In strong wind, having it stream all the time is fine — you're deliberately opening the top to depower.
Telltales on the shrouds and stays
The telltales on the sail show how the air is flowing over it. A short piece of yarn tied to a shroud, the forestay or the bridle shows something simpler: which way the wind is blowing across the boat, before it reaches the sail. Many sailors — especially on small boats — find themselves steering by these more than by the compass, and for steering that's a good instinct: they react instantly, they're at eye level, and you can see them without looking down.
Rigging them
What we use: SailZing StayTales. Graham races with them on an MC Scow. They're made for exactly this job: each one fits around the shroud and spins freely on it, so it doesn't wrap itself round the wire the way a tied-on yarn does, and they come off easily for trailering. A pack of six costs about $15 and they're sized by shroud diameter, from Melges 15 to Etchells — choose the size that matches your shrouds. They're sold by SailZing rather than on Amazon, and our link to them doesn't pay us anything.
If you'd rather make your own:
- Tie a short length of wool, or a strip of old cassette tape, to each shroud at about eye height when you're sitting where you steer, and one to the forestay or bow if you can see it. Light material reacts to the lightest air.
- Keep them clear of the sail and of anything they can wrap around. A yarn that's caught round the shroud tells you nothing.
- A masthead wind indicator does the same job higher up, in cleaner air. Boats without shrouds can use a yarn on the bridle or bow.
Steering by them
- Upwind, learn the angle your yarns sit at when the boat is in the groove, and steer to keep it there. If the yarns swing further aft, you've room to head up; if they swing forward toward the bow, bear away before the jib's windward telltales start to lift.
- In a puff, the yarns swing aft for a moment — head up and use it. In a lull they swing forward — bear away a touch to keep the boat moving. That's apparent wind at work (see true wind vs apparent wind).
- On a run, watch the yarns for the wind coming round to the side the boom is on. If they start blowing across from the leeward side, you're sailing by the lee and an accidental gybe is close — head up a few degrees.
What they can't tell you
Because they show the apparent wind, stay yarns move with every puff and lull as well as with real shifts. A lull swings them forward exactly as a header would. So use them to steer, and use your compass heading — or an app tracking the true wind — to decide whether the wind has really shifted and it's time to tack.
When telltales mislead you
- Wet or stuck telltales cling to the sail and look stalled when they aren't. Light nylon ribbon dries and frees itself better than wool, and a light spray of McLube Sailkote on the sail where each telltale sits stops them sticking in the first place.
- Spider webs and debris. A boat left on a mooring or a trailer collects spider webs, and a single strand is enough to hold a telltale or a stay yarn still. Before you leave the dock, check every telltale on the sails and the stays moves freely — none caught in a web, stuck to the cloth, wrapped round a shroud or missing.
- In very light air they hang limp whatever you do. Steer by feel, heel and other boats instead.
- Downwind the jib's luff telltales stop telling you much once you're on a run, where the sails are stalled by design.
- Telltales only describe the sail. Both can be streaming beautifully on a heading that takes you away from the mark. They say you're sailing efficiently, not that you're sailing the right way.
Doing it with Sail Tactician
Telltales tell you about the airflow; Sail Tactician tells you whether it's paying. Set the wind and your boat class first — see finding the groove.
Questions
What are the telltales on the shrouds for?
Yarns tied to the shrouds or stays show which way the apparent wind is blowing across the boat. They react instantly and sit at eye level, so many sailors steer by them; but because they move with puffs and lulls too, check your compass before deciding the wind has shifted.
What does it mean when the windward telltale lifts?
You're sailing too close to the wind, or the sail is eased too far. Bear away slightly or sheet in until it streams again.
What does it mean when the leeward telltale flutters?
The airflow on the back of the sail has stalled: you're too far off the wind or the sail is sheeted too hard. Head up slightly or ease the sheet.
Which way do you steer to the telltales?
On a tiller boat, move the tiller toward the telltale that's misbehaving. With a wheel, turn the bow away from it.
Where should telltales go on a jib?
Usually in pairs, one on each side, about 15–30 cm (6–12 in) back from the luff, at roughly a quarter, half and three-quarters of the way up. Your sailmaker's marks are the best guide.
What do leech telltales on a mainsail tell you?
Whether the back edge of the main is too tight. If the top telltale keeps disappearing behind the sail, ease the mainsheet or vang slightly.
Sources
Standard sail-trim practice as taught in club and youth racing programs. Sail Tactician behavior from the in-app User Guide and training guide, version 3.2.
What changed
- First published.
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