Telltales

Lightweight streamers used to show local airflow over a sail or wind direction around a vessel.

Pairs placed on each side of a headsail luff indicate attached or disturbed flow and help adjust sheet trim and steering. Leech telltales show flow leaving a sail, while shroud or masthead telltales can indicate local apparent wind but are affected by rig and sail disturbance.

Their interpretation depends on position, point of sail, sail design and acceleration; one fluttering streamer does not diagnose every trim problem. They can stick when wet or become turbulent in dirty air, so they should be used with sail shape, instruments and vessel response.