Apparent Wind Vector Math – Printable Charts for 10–50 km/h Speeds
We often talk about "generating our own wind." This is not a feeling. It is physics. It is Apparent Wind.
Understanding the vector math allows you to trust your gear. You can ride in light wind (8 knots) because you know that your board speed will multiply that force into a rideable 15–25 knots.
The Vector Triangle
Three forces are at play:
- True Wind (TW): The wingfoil wind measured by a stationary buoy.
- Boat Speed (BS): Your speed over the ground.
- Apparent Wind (AW): The vector sum of TW and BS. This is what hits your wing.
When you ride perpendicular to the wind (beam reach), you create a right-angled triangle. The Apparent Wind is the hypotenuse.
AW^2 = TW^2 + BS^2
The Multiplier Effect
Let's look at the math for a typical light wind day. The forecast says 10 knots (18 km/h). You pump your board to 15 knots (28 km/h).
- True Wind: 10 knots
- Rider Speed: 15 knots
- Apparent Wind: 18 knots
You have nearly doubled the power in your hands. This is why you can foil when whitecaps are barely forming. You are not riding the forecast; you are riding your own speed.
The Printable Reference Chart
Below is a reference table for a standard Beam Reach (90° to wind).
| True Wind (Knots) | Rider Speed (km/h) | Rider Speed (Knots) | Apparent Wind You Feel (Knots) |
|---|---|---|---|
| 8 kts (Light) | 20 km/h | 11 kts | 13.6 kts |
| 10 kts (Base) | 30 km/h | 16 kts | 18.8 kts |
| 12 kts (Good) | 40 km/h | 22 kts | 25.0 kts |
| 15 kts (Sweet) | 50 km/h | 27 kts | 30.8 kts |
Note: 1 Knot = 1.85 km/h
The "Mystery" Angle
As you speed up, the wind direction feels like it shifts forward. This is the "Apparent Wind Angle" (AWA).
At high speeds, the apparent wind moves closer to your nose. Even if the True Wind is hitting you from the side (90°), at 40 km/h it will feel like it is coming from 45° in front of you.
This is why you must sheet in (pull the wing tight) as you accelerate. You are chasing the vector.
Summary
Do not look at a 10-knot forecast and think "too light." Look at the chart. If you can generate 30 km/h of board speed, you are riding in 19 knots. Trust the vectors. Pump hard to start the math equation, and the physics will keep you flying.