By Sam Halberstadt · Reviewed by Marina Chen
Editor · USCG-licensed Master 50 GT · Updated May 6, 2026
Quick answer
Both telltales flying smooth and horizontal = perfect trim. Windward (inside) telltale fluttering or lifting = either trim the sheet in OR bear off. Leeward (outside) telltale fluttering or stalling = either ease the sheet OR head up. Top set behaving differently from bottom set = adjust headsail lead or main traveler.
Where to put them
Headsail (jib or genoa): three sets, port and starboard, sewn or stuck through the sail about 12 inches back from the luff. One set near the head, one at mid-luff, one near the foot. Use red yarn on port, green on starboard so you can tell sides instantly.
Mainsail: three to four telltales sewn to the leech (trailing edge) at the batten ends. These tell you about airflow exiting the sail — different information from luff telltales.
Reading the headsail telltales
Both telltales streaming horizontally on both sides = airflow attached on both faces, sail at maximum drive. This is what you're aiming for.
Windward (the side facing the wind) telltale lifting, fluttering, or twirling = the front of the sail is luffing. Either trim the sheet in tighter, or bear off (turn away from the wind) slightly.
Leeward (the side away from the wind) telltale fluttering or hanging limp = airflow has separated on the back of the sail. Either ease the sheet, or head up (turn toward the wind) slightly.
When upwind sailing, you steer to the telltales — small helm adjustments to keep both flying. When reaching, you trim to the telltales — adjust the sheet because course is fixed.
Top vs bottom telltales
If the top telltale luffs before the bottom one, your headsail lead car is too far aft — the sail is twisting too much. Move the lead forward.
If the bottom telltale luffs first, the lead is too far forward — sail not twisting enough. Move it aft. The goal is for top and bottom to break together as you slowly head up.
Mainsail leech telltales
The top leech telltale should stream straight aft 60–80% of the time, with occasional curls behind the sail. Always flowing = sail is too open (too much twist), trim the leech with mainsheet or vang. Always stalled and curled = sail is over-trimmed (closed leech), ease the sheet or drop the traveler down to leeward.
The lower leech telltales are less critical but should generally flow. A stalled lower leech with a flowing top usually means the boom is too far inboard — drop the traveler.
Light air vs heavy air
In under 5 knots, telltales hang limp because there isn't enough flow to lift them. Use a Windex (masthead vane) and watch ripples on the water for direction. Above 5 knots they should always be active — if they aren't, the sail is in serious trouble.
In heavy air, telltales work the same way, but you'll deliberately let the windward ones break occasionally to spill power and reduce heel.
Frequently asked
Sailmakers sell stick-on telltale kits with adhesive backing, or you can sew a 6-inch piece of acrylic yarn or thin spinnaker repair tape through the sail with a single stitch — one piece pierces both sides so they line up. Replace when frayed or matted.