3 min read · Updated 25 June 2026
Telltales are short lengths of yarn or tape on a sail that show how the wind is flowing across it — and they are the simplest, most useful feedback in all of sailing. Learn to read them and you can trim and steer a boat properly; ignore them and you are sailing blind. Best of all, they cost almost nothing and never stop working.
What they are
A telltale is a light strand of wool yarn or ribbon taped to a sail. You will typically find:
- A pair on each side of the headsail, near the front edge (the luff), a little way back from it.
- A set on the mainsail's leech (its trailing edge).
Because a sail works as a wing, the air flowing across it is invisible but crucial. Telltales make that airflow visible: when the flow is smooth and attached, they stream straight aft; when it breaks down, they lift, flutter or droop.
Reading the headsail telltales
The headsail telltales are the ones to watch most. The goal is both streaming straight aft — that means the sail is at the perfect angle to the wind.
- If the windward (inside) telltale lifts or flutters, you are too close to the wind: bear away, or trim the sail in.
- If the leeward (outside) telltale flutters, the sail is stalled: head up, or ease the sail out.
That simple rule — inside lifts, bear away; outside flutters, head up — is the heart of sail trim and upwind steering.
Steering upwind with telltales
Sailing upwind, telltales become your steering guide. The classic technique is to watch the windward jib telltale and steer so it is just on the verge of lifting — dancing on the edge. If it lifts, you are pinching too high; bear away a touch until it streams. If the leeward one stalls, head up. Keeping that windward telltale flickering on the edge keeps the boat sailing as high and fast as it can.
Mainsail leech telltales
The mainsail's leech telltales tell you about twist and leech tension. Ideally the top one streams aft most of the time, stalling behind the sail occasionally. If it is permanently stalled behind the sail, the leech is too tight — ease the mainsheet or add twist. This is a key part of trimming the mainsail.
Why they matter
Telltales are the great equaliser: the same tool that helps a beginner keep the sails full is what a world champion uses to find the last fraction of speed. They give instant, direct feedback on trim and steering, for free, all the time. If you learn one thing about making a boat go, learn to read the telltales — then see how to trim sails to put it to work, and the sailing terms glossary for the rest of the language.
Frequently asked questions
- What are telltales on a sail?
- Telltales are short lengths of light yarn or tape attached to a sail — usually a pair on each side of the headsail near the luff, and a set on the mainsail's leech. They show how the air is flowing across the sail. When the airflow is smooth and attached, the telltales stream straight aft; when it breaks down, they lift, flutter or droop, telling you to adjust your trim or steering.
- How do you read jib telltales?
- You want both the windward and leeward telltales streaming straight aft. If the windward (inside) telltale lifts or flutters, you are too close to the wind — bear away or trim the sail in. If the leeward (outside) telltale flutters, the sail is stalled — head up or ease the sail out. Sailing upwind, you steer so the windward telltale is just on the point of lifting.
- What do mainsail leech telltales tell you?
- The telltales on the mainsail's leech (its back edge) show whether the air is flowing off the sail cleanly. Ideally the top leech telltale streams aft most of the time, stalling behind the sail occasionally. If it is always stalled behind the sail, the leech is too tight — ease the mainsheet or add twist. If it always streams hard, the leech may be too open.
- Why are telltales useful?
- Because they make the invisible visible. You cannot see the airflow over a sail, but telltales reveal it instantly, giving direct feedback on both your sail trim and your steering. They are the simplest and most valuable instruments on the boat — free, always working, and used by beginners and world champions alike.
- How do you use telltales to steer?
- Sailing upwind, watch the windward jib telltale and steer so it is just on the verge of lifting. If it lifts, you are pinching too high — bear away slightly until it streams. If the leeward telltale stalls, you are too low — head up. Keeping the windward telltale dancing on the edge of lifting is the classic way to steer a boat upwind at its best.