How to Use Telltales to Trim Your Sails
Telltales are the cheapest and most useful sail-trim instruments on any boat. A few short strands of yarn or ribbon show you exactly how the air is flowing over your sails, so you can see when a sail is stalled, when it is luffing, and when you are steering too high or too low. Once you learn to read them, your boat will point higher, sail faster and feel more balanced.
Quick answer: when both jib telltales stream straight back, the jib is trimmed correctly. If the windward (inside) telltale lifts or flutters, you are too close to the wind or the sail is too loose: bear away or sheet in. If the leeward (outside) telltale flutters or droops, you are too far off the wind or the sail is over-sheeted: head up or ease the sheet. Two simple memory aids: push the tiller toward the fluttering telltale, or trim the sail toward the fluttering telltale.
What Are Telltales?
Telltales (also written tell-tales or tell tales) are light strips of wool, nylon ribbon or tape attached to a sail. Air flowing smoothly over the sail makes them stream straight back. When the flow separates from the surface, the telltale on that side lifts, spins or droops. Because you can see both sides of the jib through the sailcloth or a small window, telltales give you instant feedback on angle of attack, which is the key to sailing upwind efficiently. For the theory behind this, see how sailing works and how a boat sails upwind.
Don’t confuse sail telltales with a masthead wind indicator or the ribbons tied to the shrouds. Shroud telltales show the apparent wind direction; sail telltales show airflow over the sail itself.
Where Telltales Go on the Jib and Mainsail
Jib or genoa
- Usually three pairs, spaced evenly up the luff at roughly one quarter, one half and three quarters of the luff length.
- Each pair has one telltale on each side of the sail, placed about 6 to 18 inches (15 to 45 cm) back from the luff. Larger sails take them further aft.
- Set them slightly offset in height (or use a different color on each side) so you can tell which is which when you look through the sail.
- Avoid placing them too close to the luff, where they become oversensitive, or right next to a seam where they can snag.
Mainsail
- Leech telltales: short ribbons sewn to the trailing edge at each batten pocket. These are the most useful main telltales.
- Luff telltales (optional): some mains, especially on fractional rigs, have a pair or two near the luff. They are often disturbed by the mast and the jib, so most sailors rely on the leech telltales.
Reading Jib Telltales: Inside vs Outside Streaming
| What you see | What it means | Fix by steering | Fix by trimming |
|---|---|---|---|
| Both sides streaming back | Good flow on both sides | Hold your course | No change |
| Windward (inside) telltale lifting or spinning | Angle of attack too small: sail is starting to luff | Bear away (turn away from the wind) | Sheet in |
| Leeward (outside) telltale drooping or fluttering | Angle of attack too large: flow has stalled on the back of the sail | Head up (turn toward the wind) | Ease the sheet |
| Both sides fluttering | Sail far too eased or luffing | Bear away | Sheet in a lot |
On a tiller boat, the rule “push the tiller toward the fluttering telltale” always gives the right correction: tiller to windward makes the boat bear away, tiller to leeward makes it head up. On a wheel boat, turn the wheel away from the fluttering telltale instead. Many sailors simply learn: inside lifting, bear away; outside drooping, head up.
Steering Upwind by Telltales
When sailing close-hauled, the sheet is usually set and you steer by the telltales:
- Trim the jib for close-hauled sailing and hold the sheet there.
- Head up slowly until the windward telltales just begin to lift.
- Bear away slightly until they stream again. This is the edge where you point highest while keeping speed.
- Keep making small adjustments. A good helmsman watches the middle or lower windward telltale and lets it flick up occasionally.
- In waves or light air, sail a little lower (both telltales streaming, or even letting the leeward one droop slightly) to keep the boat moving. In flat water and moderate wind, you can point higher.
If you are new to the different angles to the wind, read points of sail explained first.
Top vs Bottom Telltales: Twist and Jib Lead Position
Ideally, all three windward telltales lift at about the same time as you head up. If they don’t, the jib has the wrong twist, and the jib sheet lead (car) is usually the cause.
| What happens first | Problem | Fix |
|---|---|---|
| Top windward telltale lifts first | Too much twist: the top of the sail is open | Move the jib car forward to pull the leech down (in strong winds a little extra twist is fine) |
| Bottom windward telltale lifts first | Too little twist: the top is closed and the foot is loose | Move the jib car aft |
| All lift together | Twist is about right | Leave the car where it is |
Remember to move the car forward as you roll in a furling genoa; otherwise the top of the sail twists off too much. Our guide to jib vs genoa explains why overlapping sails behave differently.
Using Mainsail Leech Telltales
The main leech telltales tell you whether air is leaving the back of the sail cleanly or stalling.
- All streaming aft: air is leaving the leech cleanly. Good when reaching, but upwind it usually means the main is too eased or twisted, so you lose pointing.
- Top telltale streaming most of the time and hiding behind the leech part of the time: the classic upwind target. Many sailmakers suggest the top telltale should stall roughly half the time when close-hauled.
- Most or all hidden behind the sail: the main is over-sheeted and the leech is stalled. Ease the mainsheet (and the vang, if it is pulling the boom down hard) until they start streaming again.
- Light air: ease the mainsheet to add twist and pull the traveler up to windward to keep the boom near the centerline; aim for the top telltale streaming.
Mainsheet tension, traveler, vang and backstay all change the leech, so leech telltales are the best way to check those controls (see mainsail controls explained). See names of sails on a sailboat if any of the terms are new.
Diagnosing Trim Problems by Telltale Pattern
| Symptom | Likely cause | Try this |
|---|---|---|
| Can’t get the windward jib telltales to stream without falling off a lot | Jib over-eased or lead too far aft | Sheet in; move the car forward |
| Leeward jib telltales stall even when sailing low | Jib over-sheeted | Ease the sheet a little |
| Boat points well but feels slow | Sails too flat or over-sheeted for the conditions | Ease the sheets slightly, sail a few degrees lower |
| Main leech telltales always hidden and heavy weather helm | Main over-sheeted or too full | Ease the mainsheet, drop the traveler, flatten the sail |
| Telltales stuck to the sail | Wet or static | Replace wool with nylon or coated telltales |
Telltales Off the Wind
On a beam reach, the jib telltales still work: trim the sheet until both sides stream. On a broad reach and run, the flow becomes less regular and telltales are less useful; trim by easing the sail until it just begins to luff, then pull in a little. Spinnaker and gennaker trimmers rely on the luff curl rather than telltales.
Installing or Replacing Telltales
- Use light, water-shedding material. Nylon ripstop strips or ready-made sail telltales are better than wool, which absorbs water and sticks to the sail.
- Make them about 6 to 10 inches (15 to 25 cm) long.
- Attach with self-adhesive sail-repair patches or small sailmaker’s tape circles on each side, or thread them through the sail with a needle and knot each end.
- Use different colors for port and starboard (for example red on port, green on starboard) so you can tell them apart through the sail.
- Check them every season. Faded, torn or missing telltales are easy and cheap to replace.
Telltales and Boat Balance
Well-trimmed sails also affect how the boat steers. An over-sheeted main increases heel and weather helm, while a stalled jib reduces drive. If the boat still feels overpowered even with good telltale trim, it is usually time to reef.
Sail Telltales: Summary
Put three pairs of telltales on your jib about 6 to 18 inches back from the luff and ribbons on the main leech. Upwind, hold the sheet and steer: inside telltale lifting, bear away; outside telltale drooping, head up. Use the top and bottom telltales to set the jib car, and the main leech telltales to set mainsheet and twist. A few minutes of practice watching them will make every point of sail faster and easier.
