Two Types of Drag
Every foil fights two forms of resistance. Understanding them helps you choose the right equipment for the conditions.
- Form drag: Resistance from the surface area and shape of your foil. Wider, chunkier foils push more water aside.
- Skin friction: Resistance from water molecules clinging to the foil surface. Even smooth foils create friction.
Drag Comparison
Form Drag
Shape resistance
Increases with foil thickness and surface area
Dominant at low speeds
Skin Friction
Surface resistance
Increases with foil surface roughness
Dominant at high speeds
Why Chop Increases Drag
Chop changes your pitch angle constantly. Every sudden lift or drop increases drag exponentially. When chop hits the nose of your board, the board pushes water aside violently. This creates massive resistance spikes.
In smooth water, your foil cuts through cleanly. In choppy conditions, you're essentially plowing water.
The Speed Formula
Drag increases with the square of your speed. Double your speed, and drag quadruples. This is why slower, thicker foils work better in chop—they let you ride at lower speeds without stalling.
Reducing Drag
Match your foil to the conditions:
- Light wind, flat water: Use thin, high-aspect foils. Minimal drag, maximum glide.
- Strong wind, choppy water: Use thicker, lower-aspect foils. You can ride slower and maintain control.
- Downwind runs: High-aspect foils with sharp leading edges cut through bumps cleanly.
Practical Drag Reduction
Keep foil surfaces clean and smooth
Ride at optimal angle of attack (minimal pitch changes)
Choose foil size based on wind and water state, not just your weight
Summary
Drag increases dramatically in chop and messy swell. Choose a foil that can keep gliding at your target speed without forcing you to fight the water. Clean technique reduces drag more than any equipment choice.