What is VMG (velocity made good) in sailing?
VMG is your speed towards the wind or the mark, not your speed through the water. How it is calculated, why sailing slower can be faster, what it does not tell you, and how to read it after a session.
By the Waterspeed team
VMG, velocity made good, is how fast you are getting closer to where you want to go: upwind to the windward mark, or downwind away from it. It is your boat speed multiplied by the cosine of the angle between your course and that direction. Sailing slightly slower at a tighter angle often gives a better VMG than sailing fast and wide.
How is VMG calculated?
VMG = boat speed × cos(angle between your course and the target direction).
Upwind, the target direction is straight into the wind, so the angle is your true wind angle (TWA). Downwind it is straight away from the wind, so the angle is 180° minus your TWA.
Why can sailing slower be faster?
Three upwind examples:
| Boat speed | True wind angle | VMG upwind |
|---|---|---|
| 5.5 knots | 40° | 4.21 knots |
| 6.0 knots | 45° | 4.24 knots |
| 6.5 knots | 50° | 4.18 knots |
The fastest boat (6.5 knots) has the worst VMG because it sails 10° wider. Here the best VMG is at 45°.
Downwind it works the other way:
| Boat speed | True wind angle | VMG downwind |
|---|---|---|
| 8 knots | 140° | 6.13 knots |
| 9 knots | 135° | 6.36 knots |
| 10 knots | 120° | 5.00 knots |
Heating up to 135° pays; going much higher adds speed but loses VMG. Foiling boards and fast boats move the best angle, which is why your own numbers matter more than rules of thumb.
What doesn’t VMG tell you?
- Current and tide. GPS measures speed over ground, so VMG includes the current’s push or drag.
- Wind shifts. VMG depends on the wind direction you use. If the wind shifts and the reference doesn’t, VMG drifts too.
- Tactics. The best VMG on one tack isn’t always the best race: shifts, pressure and traffic decide where to go.
How does Waterspeed show VMG?
Waterspeed Ultra calculates VMG from your GPS track and the session’s wind direction, downloaded from the forecast or set by you. It splits the session into upwind and downwind legs and the runs between manoeuvres, stars your best leg by average VMG, shows the VMG change through each tack and gybe, and draws a polar chart of your own speed at each wind angle. It works for sailing, windsurfing, kitesurfing, kitefoil, wingfoil and windfoil.
Two limits to know: it uses one average wind direction for the whole session, not the shifts during it; and the polar chart is built from your own track, so it is your polar, not a class polar. Advanced Analyses in the help centre
What is a good VMG?
There’s no single number; it depends on the boat and the wind. Compare your legs with each other: Waterspeed colours a leg green within 10% of your best, orange at 10–20% and red beyond 20%. Most boats sail their best upwind VMG somewhere around 40° to 50° true wind angle and downwind around 130° to 150°.
Next: Upwind angles and VMG in a dinghy and Sailing performance metrics.
