Mainsail telltales are light-weight streamers attached to the back edge of the mainsail. They show whether the wind is flowing cleanly off the sail or whether the flow is stalled, shown by the telltale disappearing behind the sail.  The top telltale stalls first because the sail is narrowest at the top; therefore, the trimmer should concentrate on the top telltale when tightening the mainsheet. Telltales come standard on all UK Sailmakers mainsails.  

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