Sailing Velocity Made Good (VMG) Calculator
Calculate sailing VMG to windward or leeward by boat speed and wind angle.
Find optimal pointing angle and tacking strategy for upwind and downwind legs.
Velocity Made Good (VMG)
VMG is the component of boat speed projected onto the wind axis (or any other target axis). It tells you how fast you’re actually closing on a windward or leeward mark, accounting for the angle you’re sailing at.
The formula: VMG = Boat Speed × cos(Angle to wind)
For upwind: angle is the true wind angle (TWA). For downwind: same formula with TWA over 90°.
Key insight:
- Pointing higher (smaller angle) reduces speed but increases the cosine factor — usually a wash
- Bearing off (larger angle) increases speed but reduces projection
- The optimal angle depends on the boat’s polar curve
Typical optimal upwind angles by boat:
| Boat Type | Optimal TWA Upwind | Optimal TWA Downwind |
|---|---|---|
| Cruiser/racer (40-ft, masthead) | 40-45° | 145-160° |
| Performance racer (J/105, J/111) | 32-40° | 130-150° |
| Modern foiling (IMOCA, AC75) | 25-30° | 110-130° |
| Day sailer (Laser, etc.) | 38-45° | 150-160° |
| Cruising catamaran | 45-55° | 135-150° |
| Multi-hull racer | 35-50° | 130-140° |
Reading polar diagrams: A polar diagram shows boat speed at every wind angle and wind speed combination. The VMG sweet spot is the angle where the polar curve’s tangent is perpendicular to the wind.
Example:
- Boat speed 6 kts at 40° TWA: VMG = 6 × cos(40°) = 4.6 kts to windward
- Boat speed 7 kts at 50° TWA: VMG = 7 × cos(50°) = 4.5 kts to windward
So pointing tighter wins by 0.1 kts even though boat speed is 1 kt slower. This is why competitive sailors point hard upwind.
Lay line strategy:
- Sail toward the lay line on the lifted tack when possible
- Don’t overstand the mark — every meter past the lay line is wasted
- In oscillating wind, tack on headers to stay on the lifted tack
Headers and lifts:
- Header: wind shifts forward (closer to bow) — tack to gain
- Lift: wind shifts aft (further from bow) — stay on this tack and ride it
Apparent vs True wind:
- TWA (True Wind Angle): angle from wind direction — used for VMG calculation
- AWA (Apparent Wind Angle): wind angle felt by the moving boat — what trim is set to
- For close-hauled, AWA is typically 25-35° while TWA is 35-50°
Practical use:
- Watch boat speed and angle on instruments
- Calculate VMG mentally: speed × cos(TWA) for upwind
- Adjust pointing to maximize VMG, not raw speed
- In light air, bear off slightly for boat speed; in heavy air, point higher
Modern instruments (B&G, Garmin, Raymarine) calculate VMG automatically from GPS speed, wind angle, and wind speed. Old-school sailors keep mental models for backup.