Not All Swells Are Equal
Two swells can both be "3 feet high," but one creates epic glide bumps while the other is unrideable chop. The difference is swell energy—a measure that combines height and period into a single meaningful number.
Energy reveals the true power in a swell.
Swell Energy Formula
Energy (kJ/m) ≈ Height² × Period
Example: 2ft (0.6m) wave at 12s period = 0.36 × 12 = 4.3 kJ/m
A short period wave with the same height has dramatically less energy
Why Energy Matters
High energy swells behave differently than low energy chop:
- Power delivery: High energy = sustained push, easy glide
- Organization: High energy swells line up cleanly
- Travel distance: More energy = further travel without decay
- Downwind worthiness: Need energy to maintain bump connections
Energy Thresholds for Foiling
Different disciplines require different energy levels:
Energy Level Guide
<100 kJ
Poor
Local chop, cluttered, short bumps. Not worth downwinding.
100-200 kJ
Marginal
Usable for experienced riders. Short glide windows. Pump-heavy.
200-500 kJ
Good
Clean lines, good bump connection, proper downwind conditions.
500+ kJ
Epic
Powerful, organized, effortless gliding. Premium downwind.
Reading Forecast Charts
Most forecasts show swell energy as colored bars or numbers. Here's how to use them:
- Look for tall bars: Height on energy chart indicates total power
- Compare multiple swells: Ride the highest energy direction
- Check period breakdown: High energy from long period = good. High energy from short period = messy.
- Track swell age: Energy decreases as swell travels and decays
Energy vs Quality Grid
Low Energy + Short Period
Worst case
Cluttered chop, no glide, skip it
High Energy + Short Period
Mixed bag
Powerful but messy, tight bumps
Low Energy + Long Period
Rideable
Clean but weak, pump required
High Energy + Long Period
Best case
Clean, powerful glide paradise
Summary
Use energy charts, not height alone. Target 200+ kJ for good downwind sessions, 500+ kJ for epic conditions. High energy swells create long, powerful bumps with clean lines. Low energy swells produce cluttered chop.