Friction at the Surface
Water isn't perfectly smooth. Even small waves create friction against the air moving above them. This friction slows down the wind at the very bottom layer—right where your board sits.
The effect is dramatic: wind speed at the surface can be 30-50% weaker than the wind just a few meters higher.
The Logarithmic Wind Profile
Wind speed increases with height following a logarithmic curve. This is called the "wind gradient" or "wind shear layer." The steepest increase happens in the first 10 meters above the surface.
Formula: Wind speed = Wind₁₀ₘ × (ln(z/z₀) / ln(10/z₀))
The Vertical Difference
As you go higher, friction from the surface disappears. The wind accelerates because there's nothing slowing it down.
At 3 meters above the water (standard wing height when riding), the wind can be 10-20% stronger than at the surface. This vertical difference is the wind gradient.
Wind Speed by Height
0m (Board Level)
Surface friction zone
10 kts
1m (Waist Height)
Moderate friction
11 kts
3m (Wing Height)
Minimal friction
12 kts
Example assumes 10 knots forecast at 10m standard height
Why This Matters for Riding
The wind gradient directly affects your ability to ride:
- Starting from water: Your wing is in the weakest wind layer. Hard to generate power.
- Wing raised high: You access stronger wind 2-3m up. Easier to pump onto foil.
- Once flying: Your whole stance is higher, putting you in stronger average wind.
- Light wind sessions: The gradient difference can mean the difference between foiling and sinking.
Technique Implications
Beginners often let their wing droop near the water where the wind is weakest. To get moving, you must:
- Raise the wing high: Fully extended arms, wing tip above head height
- Reach into clean air: You're escaping the friction layer
- Maintain height while riding: Don't let the wing drop during transitions
- Use the gradient for pumping: Lift wing on upstroke to harvest stronger wind
Practical Wind Gradient Tactics
In light wind (<12 knots), keep wing as high as possible—height = power
When water-starting, extend arms fully before attempting to pump
In lulls, lift wing higher rather than pulling harder
Once foiling, your body is higher—this "bonus" wind helps maintain speed
Summary
Keep your wing high. The wind is 10-20% stronger just a few meters above the surface. Don't let the wing tip drag in the "dead air" near the water. Understanding the wind gradient is especially critical in light wind conditions where every knot counts.