Reading TellTails

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How to read jib telltales for beginners?

Reading jib telltales is one of the simplest yet most effective ways to trim your sails properly — especially on the River Thames, where the wind changes more often than a British forecast. Here’s a beginner’s guide to make sense of those little ribbons:

What Are Telltales?

Telltales are small strips of wool, yarn, or ribbon (often red and green) attached to the luff of the jib (the front edge). They show the airflow over the sail.

You’ll usually have two telltales on each side of the jib — one windward side (facing the wind) and one leeward side (away from the wind). On the RS Toura we have three sets, one low, one set halfway up the sail and one near the top of the sail.

Which set do you watch - all of them.

We also have telltales on the edge of the mainsail. Paul pointed them out to me. I hadn't noticed them.

Basic Setup

When sailing upwind or on a reach:

✅ Good Trim = Both telltales streaming horizontally, flowing backwards.
❌ Bad Trim = One or both telltales flapping, lifting, or dancing.

How to Read Them

Telltale Behaviour	What It Means	What To Do
✅ Both streaming backward	Perfect airflow – hold your course!	Do nothing (for 5 seconds anyway)
🔼 Windward telltale lifting	You're pointing too high into wind	Bear away (turn slightly away)
🔽 Leeward telltale lifting	You're too far off the wind	Head up (turn slightly into wind)
🎯 Both fluttering/flapping	Sail not trimmed or stalled	Trim sail in / adjust heading

A good rule of thumb that works for both tacks is – if one telltale is flapping then move the sail towards the flapping telltale.

Top Tips

Small adjustments: Tiny tiller movements or a few inches of sheet change make all the difference.
Keep watching: Check every 5–10 seconds — on a river like the Thames, the wind changes constantly.
Don’t chase perfection: You’ll go mad. Aim for "mostly right, most of the time".