Wing Size vs Air Density Tables – Summer Tropical vs Winter Polar Corrections
You have a favorite 5m wing. In the winter, it feels powerful in 15 knots. In the summer, in the same 15 knots, it feels gutless. You aren't crazy. The air changed weight.
Air density ($\rho$) changes with temperature. Cold air is dense (packed with molecules). Warm air is thin. The power in the wingfoil wind is directly proportional to this density.
The Physics of Density
The formula for wind power is $P = 0.5 \cdot \rho \cdot V^3$.
- $\rho$ (Density) drops by about 10% when temperature rises from 5°C to 30°C.
- This means 15 knots in the Tropics has 10–15% less torque than 15 knots in the Arctic.
The Correction Tables
Use these tables to adjust your forecast expectations.
Baseline: 80kg Rider, Standard 5m Wing.
| Temperature | Air Density | Real Feel of 15 Knots | Recommended Wing |
|---|---|---|---|
| 0°C (Winter) | 1.29 kg/m³ | 17 Knots | 4.5m |
| 15°C (Spring) | 1.22 kg/m³ | 15 Knots | 5.0m |
| 30°C (Summer) | 1.16 kg/m³ | 13 Knots | 6.0m |
Impact on the "Low End"
This effect is most critical in light wind. If the forecast predicts 10 knots on a hot day (30°C), the air is too thin to support you. It will feel like 8 knots. You need a 7m wing. If the meteogram predicts 10 knots on a freezing day (0°C), the dense air will punch harder. You might get away with a 5.5m.
Thermal Wind Density
Note that thermal wind (sea breeze) is usually cooler than the land air, but often warmer than a gradient winter wind. A sea breeze at 20 knots in the Caribbean is "soft." It is easy to handle. A Gradient wind at 20 knots in Scotland is "heavy." It hits the wing with more mass.
Summary
Stop looking at knots as the only number. Look at the temperature.
- Hot Day: Rig bigger (+1 size).
- Cold Day: Rig smaller (-0.5 size).
- Travel: If you go to the equator, bring your big light-wind gear. The thin air will rob your power.