Telltales are short pieces of wool or ribbon attached to a sail, one on each side, that show how the air is flowing over it. When both stream back smoothly the sail is trimmed well; when one lifts or droops the sail needs adjusting.
Telltales are light strips of wool, yarn or thin ribbon fixed to a sail to show how the air is flowing over it.
On the jib, telltales are fitted in pairs a short distance behind the luff, one on each side of the sail, usually with two or three pairs at different heights. The sail is thin enough that you can see the far one through the cloth. They are often in two colours, so the windward and leeward ones are easy to tell apart.
What they show:
- Both streaming straight back: the air is flowing smoothly over both sides, and the sail is producing as much drive as it can.
- The windward one lifting or fluttering: the sail is let out too far, or the boat is steering too close to the wind. The wind is striking the luff on its leeward side, and the flow on the windward side has broken away.
- The leeward one drooping or spinning: the sail is pulled in too far, or the boat has turned too far away from the wind. The air on the leeward side has broken away and the sail has stalled.
The mainsail often has telltales on its leech, the back edge, usually at the ends of the batten pockets. When they stream out behind the sail the main is trimmed well. When they keep disappearing round to leeward, the leech is too tight and the top of the sail is stalling: ease the mainsheet or the kicker.
Many boats also have telltales on the shrouds, or a wind indicator at the masthead, which show the apparent wind direction rather than the flow over the sail.
Telltales are most useful from close-hauled to a broad reach. On a dead run, with the sails let right out and the wind pushing on them, the airflow is stalled anyway, and the jib telltales tell you little.
More in the book: Chapter 5, Trimming the sails