Swell Train Spacing – The 100–200 m Gap That Creates Perfect Downwind Runs
You see a forecast for 4-foot waves. You think it will be epic. You get out there, and it is a messy, confused washing machine. You pump your legs until they burn, but you never find the flow.
The problem is not the height. It is the spacing. In wingfoiling, the "wavelength" (distance between crests) dictates your speed.
The Golden Gap (100–200 Meters)
For a wingfoiler on a high-aspect foil, the magic number is a swell period of 8 to 12 seconds.
Physics dictates the wavelength based on period:
- 8 Seconds: ~100 meters spacing.
- 12 Seconds: ~225 meters spacing.
This 100–200 meter gap is the "Glider Zone." It provides a long, gentle slope. You can drop the wing to your side and glide for 20 seconds without pumping.
If the period is too short (5 seconds / 40 meters), the slope is too steep. You crash into the trough. If the period is too long (16 seconds / 400 meters), the wave moves too fast (30 knots) for you to catch it.
Reading the "Corduroy"
When you stand on the beach, look at the horizon. Do not look at the whitecaps (which show wind gusts). Look at the dark lines of the swell.
- Messy Chaos: The lines are broken. The spacing varies. This is local wind swell. It requires constant pumping.
- Clean Corduroy: The lines are parallel and evenly spaced. This is groundswell.
You want the corduroy. The 100–200 meter gap allows you to link turns. You turn down the face to accelerate, then carve up the face to brake. You stay in the power pocket.
The Overtake Speed
To catch a swell, you must match its speed.
- 8s Wave: Travels at ~12 knots. Easy to catch.
- 12s Wave: Travels at ~19 knots. Requires a fast foil and efficient board.
If the wind speed is 20 knots but the swell is traveling at 25 knots (15s period), the waves will pass underneath you. You cannot catch them. You want the wingfoil wind to be slightly faster than the waves.
Summary
Stop obsessing over wave height. A 2-foot wave with a 200-meter gap is a dream downwinder. A 6-foot wave with a 40-meter gap is a nightmare. Check the swell period on your meteogram. Aim for 8–12 seconds.