Sailboat Heeling Angle Calculator
Estimate a sailboat heeling angle from wind pressure and righting moment.
Understand the stability trade-off for different sail configurations.
A sailboat heels (tilts sideways) when the heeling force from the sails exceeds the boat’s initial righting moment. The angle of heel is a function of wind force on the sails and the boat’s stability characteristics.
Simplified formula: Heel angle ≈ arctan(Heeling Moment / Righting Moment) Heeling Moment = Wind force × Center of Effort height above waterline Righting Moment = Displacement × GM × sin(heel) (for small angles: RM ≈ Δ × GM × heel_rad)
Wind pressure on sails: P = 0.00338 × V² (lbs/ft² where V is apparent wind in knots) Heeling Force = P × Sail Area × sin(apparent wind angle)
Metacentric height (GM): Determines initial stability. Enter GM in feet, the same unit this calculator uses for its stiffness bands:
- Tender (GM under 2 ft): light racing keelboat, quick to heel with smooth motion
- Moderate (GM 2–5 ft): typical cruising-yacht stiffness
- Stiff (GM 5–9 ft): beamy, hard-chined, or heavy-keeled, with quick righting but jerkier motion
Comfort ranges:
- 0–15°: Comfortable, full sail
- 15–25°: Normal sailing angle, the performance sweet spot; loose gear starts to slide
- 25–30°: Pressed, flatten the boat
- 30–40°: Uncomfortable, reef now
- Over 40°: Excessive, round up and reduce sail
Practical note: Modern offshore racing yachts regularly sail at 20–25° heel for speed. Cruising sailors typically prefer 15–20°. More than 30° sustained heel suggests too much sail for conditions.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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