VMG, Polars and Wind Angles: Sailing Performance Metrics Explained

OpenWater Guides · Updated July 31, 2026

Why the fastest heading isn't the best heading

Point straight at an upwind mark and you stop — you can't sail into the wind. Bear off for speed and you're fast in the wrong direction. Between those extremes is an optimum: the angle where progress toward the mark peaks even though raw speed doesn't. That's your VMG angle, and it's usually tighter than feels fast. The same logic applies downwind: on most craft, especially foils, a series of hot angles and gybes beats sailing dead downwind.

Reading a polar curve

Imagine standing at the center of a compass with the wind blowing from the top. Your polar curve traces how fast you go at each heading: zero in the no-go zone near the wind, swelling through the beam reaches (usually the fastest raw speed), and narrowing again dead downwind. Two tangent points matter:

• Upwind VMG angle — where the curve's vertical (upwind) component peaks, commonly 40–55° off the true wind for foiling craft.
• Downwind VMG angle — the same idea mirrored, often 135–160° depending on the craft.

Your polar is personal: it reflects your gear, your weight and your technique. Which is exactly why recording it is useful.

Tacking and gybing angles

Your tacking angle is the direction change between one upwind tack and the other — a direct, honest measure of upwind efficiency. Wing foilers typically tack through 90–110°; wider than ~120° means you're giving away height. The gybing angle tells the equivalent story downwind. Comparing port and starboard reveals asymmetries almost everyone has and almost no one knows about.

Getting wind direction without a wind sensor

You don't need instruments to compute any of this. Because an out-and-back session sweeps many headings, the wind direction can be inferred from the track itself — the axis of symmetry of your speeds and headings. OpenWater works out the wind direction from your own track with no weather service and no internet, then computes your polar curve, VMG upwind and downwind, tacking and gybing angles, and a port-versus-starboard comparison for every session.

Using the numbers to get faster

1. Find your current VMG angles from a few recorded sessions.
2. Test one change at a time — footstrap position, wing size, stance — and compare polars, not feelings.
3. Attack your weak side. The port/starboard split typically shows a 5–15% asymmetry; closing it is free speed.
4. Watch the trend, not the session. Wind varies; medians across sessions tell the truth.