Sailboat Heeling Angle Calculator

A sailboat heels (tilts sideways) because the sails push it over and the hull and keel push it back. It comes to rest at the angle where those two efforts balance, and that angle is what this calculator estimates.

Where the formula comes from

As the boat heels, the sail presents less of itself square to the wind, so the heeling moment falls off with cos(θ). Meanwhile the righting moment grows with sin(θ), because the keel’s lever arm opens up. Set the two equal:

Heeling Moment × cos(θ) = Displacement × GM (metacentric height) × sin(θ)

Divide through and the heel angle drops out on its own:

tan(θ) = Heeling Moment ÷ (Displacement × GM)

which is the line this calculator actually solves. Heeling Moment is the sail force times the height of the centre of effort above the waterline.

Wind pressure on sails: P = 0.00338 × V² (lb/ft², V in knots apparent) Heeling Force = P × Sail Area

That pressure constant is the standard dynamic-pressure figure converted from miles per hour to knots. The calculator assumes the wind is on the beam, which is the worst case: sailing closer to head to wind reduces the side force roughly with the sine of the apparent wind angle, so a close-hauled boat in the same breeze heels less than this figure suggests. Flat-plate pressure also understates a well-trimmed sail, which generates lift rather than simply blocking air, so treat the answer as a floor.

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.