Learning how to use telltales helps you see otherwise invisible wind. You’re sailing along, sails full, and the boat feels fine. But is it fast?
You can’t answer that question by intuition alone. A few strips of yarn will show you which line to adjust and which way to steer.
This guide covers jib telltales, mainsail telltales, and where to place them. You’ll also learn what they indicate at every point of sail. By the end, you’ll read them with ease.
What Are Telltales?
Telltales are short strips of yarn, ribbon, or sailcloth attached to both sides of a sail. As wind flows over the cloth, they either stream aft or flutter.
You can't see the wind, so the yarn shows you how it’s moving. Start at the sail’s two edges. The luff is the forward edge of the sail, and the leech is the trailing edge.
Three sets of telltales per sail: Space them at one quarter, one half, and three quarters of the hoist. The hoist is the sail's height from tack to head.
Twelve inches aft of the luff, minimum: A thick headfoil or padded luff churns the air. Push the front set back to 16 inches.
Away from seams: Yarn snags on stitching and gives you a false reading.
Lowest set in the helmsperson's sightline: The driver steers by that set. It has to be visible from the wheel.
Roller-reefed headsails need one more step. Rolling the sail around the forestay leaves every telltale closer to the new luff. A full vertical row of telltales provides coverage at any reef.
Four Telltale Signals Every Sailor Should Recognize
Four patterns cover nearly every telltale behavior you'll encounter. Each one points to a different airflow problem and a different correction.
Both streaming straight back: Air hugs both sides of the sail. That's attached flow, so leave the sheet alone.
Windward telltale lifts or flutters: The front of the sail is luffing and no longer pulling. Trim toward the fluttering telltale, or bear away a few degrees.
Leeward telltale flutters or droops: Air has separated on the leeward side, and the sail has stalled. Ease the sheet, or bear away until flow reattaches.
Both hanging limp: You've trimmed too hard, and air isn't circulating. Ease out slowly until both wake up.
Here's the shortcut. If the windward telltale flutters, trim toward it or bear away; if the leeward telltale flutters, ease the sheet or head up. Pair that with a check of the draft position, and you'll diagnose most trim problems.
How to Use Telltales on the Jib for Speed and Height
The jib does double duty. Its luff telltales tell the driver where to steer. Its leech telltales tell the trimmer how hard to sheet.
Find the Groove and Steer It
The groove is the narrow band of steering angles where airflow over the jib stays attached on both sides. Keep every telltale streaming aft, and you're in it.
In medium air, ride the high side of that groove. Let the windward telltale lift to about 45 degrees. The boat points closer to the wind and gives up almost nothing in speed.
Let it lift past 45 degrees, and the front of the jib starts luffing. Bear away two degrees, and the jib settles.
Diagnose Your Jib Lead Position
The jib lead car anchors the sheet on deck, and its position governs how the sail twists. Head up slowly and watch which set of telltales lifts first.
Top set lifts first: The lead has crept too far aft. It flattens the foot and opens the head too much.
Bottom set lifts first: The lead has crept too far forward. It closes the top and cuts off airflow at the leech.
Top lifts a beat before the bottom: That's your target. The head opens in puffs and spills breeze before the boat heels too far.
Move the car an inch at a time and test again on both tacks. A one-inch adjustment shows up in the telltales.
Read the Slot at the Jib Leech
Leech telltales check the slot, the narrow space between the jib and the mainsail. Air accelerates through the area, and the telltales indicate whether it escapes without obstruction.
Aim for leech telltales flowing 90 to 100 percent of the time. A telltale that vanishes behind the sail means you've over-trimmed the jib or squeezed the slot shut. A loose halyard can round the leech, making the telltales vanish behind the sail.
In flat water and moderate breeze, trim until the leech telltales start to stall, then ease an inch. If the boat feels sluggish and bound up, ease the jib sheet again.
How to Read Mainsail Telltales for Twist
Twist is the difference in trim angle between the head and foot of the sail. Wind aloft is stronger and comes from a wider angle, so the head opens further.
Most cruisers put telltales only on the mainsail leech, and they're right to do so. Mast turbulence disturbs air at the front of the sail, so body telltales flutter for no reason. Lazyjacks damage body telltales too.
The one worth watching is on the top batten. Sailmakers often use red yarn there so you can spot it against the sky.
On a reach, add boom vang until the top telltale starts to stall, then ease slightly. Too much twist spills drive out of the head. Too little chokes the air leaving the leech and adds drag.
Your battens also govern how much twist you can dial in. Read the tradeoffs between full and partial battens before you touch the vang.
Upwind, you get a choice. Pointing mode trades speed for height, so sheet hard enough that the top telltale stalls now and then. For acceleration out of a tack, keep every leech telltale streaming.
Telltale Trim on Every Point of Sail
The same signals mean different things depending on your point of sail. Here's what to expect on each heading.
Upwind
Keep the windward telltales on the verge of lifting. An occasional lift and a shiver in the luff are fine. They tell you the apparent wind is as far forward as it goes.
Light air calls for a different approach. Skip pointing mode and keep both telltales streaming, since stalling in five-knot winds kills your momentum.
Heavy air flips it again. The feather rises in the puffs, meaning you should tilt your head a few degrees toward the wind. Your heel angle levels out, and you stop fighting the helm.
On a Reach
Reaching asks you to compromise. Wind velocity and angle differ between the masthead and deck level. No setting satisfies the three telltale sets.
Trim the middle set to perfection and accept the rest. The top windward telltale will lift a little. The bottom leeward one may droop and stall, which is normal here.
Downwind
Deep downwind, your sails quit acting as airfoils and catch air like parachutes. Telltales stop streaming and are drawn behind the cloth.
Ignore them here. Set your twist by keeping the top batten parallel to the boom. Check the masthead vane to determine the wind angle.
Put Telltales Into Practice on a Sailing Virgins Course
Reading telltales is a skill that improves with practice. It takes time at the helm, ideally with an instructor guiding you on how to interpret the yarn's behavior.
Our week-long liveaboard monohull courses put you on a keelboat every day. You sleep aboard, so the practice doesn't end when the sun goes down. Trade wind conditions in the British Virgin Islands hand you puffs, lulls, and wind swings in one afternoon.
You'll earn ASA 101, 103, and 104 certifications along the way. That combination qualifies you to bareboat-charter a monohull in many destinations. Beginners need no experience at all, and our instructors match you to the right level.
Those instructors have decades of experience on monohulls. They teach you how to use telltales in shifting breezes. Choose your course, book your week, and come home reading the yarn without a second thought.