Pulling the mainsheet in tighter feels like it should always add power, the sail pulled taut and flat against the wind, but past a certain point that tighter trim doesn’t produce more speed at all — it pushes the airflow over the sail into a stall, the same way an overtrimmed wing loses lift.

Why Overtrimming Approaches a Stalled Airflow Angle

The mechanism: pulling-a-sail-in-past-its-optimal-angle-disrupts-the-smooth-airflow-across-its-surface-in-a-way-that-mirrors-an-aircraft-wing-stalling-at-too-steep-an-angle (pulling a sail in past its specific optimal angle disrupting the smooth, attached airflow across its curved surface in a way that closely mirrors an aircraft wing stalling at too steep an angle of attack, per the sailing-basics-terminology-guide logic — pulling-a-sail-in-past-its-specific-optimal-angle-disrupting-the-smooth-attached-airflow-across-its-curved-surface-in-a-way-that-closely-mirrors-an-aircraft-wing-stalling-at-too-steep-an-angle), and the reframe (more tension producing turbulence instead of more lift past a threshold)).

Why That Stall Isn’t Obvious From the Deck

The concealment: a-stalled-sail-still-looks-full-and-taut-from-the-cockpit-giving-no-visual-signal-that-airflow-has-actually-separated-from-its-surface (a stalled sail still looking entirely full and taut from the cockpit, giving a sailor no clear visual signal at all that airflow has actually separated from its surface and stopped generating usable forward power, per the sailing-fitness-guide logic — a-stalled-sail-still-looking-entirely-full-and-taut-from-the-cockpit-giving-no-clear-visual-signal-that-airflow-has-actually-separated-from-its-surface-and-stopped-generating-usable-forward-power), and the frame (the visual cue people rely on being unable to detect the actual problem)).

How to Ease Out Gradually to Find the Actual Power Point

The adjustment: ease-the-sail-out-slowly-until-a-slight-luff-appears-at-the-front-edge-then-trim-back-in-just-until-it-disappears-to-locate-the-true-maximum-power-angle (easing the sail out slowly until a slight luff, or flutter, appears right at its front edge, then trimming back in just until that flutter disappears, as a way to actually locate the true maximum-power angle rather than guessing at it, per the what-to-expect-your-first-time-sailing-guide logic — easing-the-sail-out-slowly-until-a-slight-luff-appears-right-at-its-front-edge-then-trimming-back-in-just-until-that-flutter-disappears-to-actually-locate-the-true-maximum-power-angle), and the frame (using a visible edge signal instead of a feel-based guess)).

Pulling a sail in past its optimal angle disrupts the smooth airflow across its surface in a way that mirrors a wing stalling at too steep an angle, yet a stalled sail still looks entirely full and taut from the cockpit, giving no visual sign that it has actually stopped generating usable power. Easing the sail out slowly until a slight luff appears at its front edge, then trimming back in just until that flutter disappears, locates the true maximum-power angle using a visible signal instead of a guess.