Reading waves: height is only half the story
Two numbers describe every sea state on Blue Wake: height (feet) and period(seconds). The same 3 ft of water can be an easy cruise or a teeth-rattler — the period is what decides which.
The two numbers
How tall the waves are, trough to crest. Buoys report significant wave height — the average of the biggest third of the waves — which is about what an experienced eye calls the sea. Expect occasional sets noticeably bigger than the number.
The seconds between one crest and the next passing a fixed point. It sets how much room each wave has: longer period = longer, more stretched-out waves; short period = waves crowded close together.
Why short period feels so much worse
Picture 3 ft waves. On a 9-second period they're long, rolling ramps a hundred-plus feet apart — the bow rises and settles, and it reads as a gentle swell. Squeeze those same 3 ft into a 4-second period and each wave is a short, steep wall arriving right after the last: the hull can't finish one before it hits the next. That's Great Lakes chop — it pounds, throws spray, and slows you down.
The physics is steepness: for the same height, a wave's length shrinks with the squareof the period, so halving the period makes the ride roughly four times steeper. That's why our labels (and the score) come from the height-and-period pair, never from either number alone.
How the pair maps to our labels
This grid is generated from the exact rule the app uses, so the tiles and this page always agree. Down the left is wave height; across the top is period. Notice the two diagonals: short period pushes toward chop, long period (8 s+) with easy height reads as swell— and under a foot of water it's simply calm, whatever the period.
| ft \ s | 2s | 3s | 4s | 5s | 6s | 7s | 8s | 10s |
|---|---|---|---|---|---|---|---|---|
| 0.5 ft | calm | calm | calm | calm | calm | calm | calm | calm |
| 1 ft | light chop | light chop | light chop | light chop | light chop | light chop | rolling swell | rolling swell |
| 1.5 ft | steep chop | steep chop | light chop | light chop | light chop | light chop | rolling swell | rolling swell |
| 2 ft | steep chop | steep chop | steep chop | light chop | light chop | light chop | rolling swell | rolling swell |
| 3 ft | steep chop | steep chop | steep chop | steep chop | moderate chop | moderate chop | rolling swell | rolling swell |
| 4 ft | rough | rough | rough | rough | rough | rough | big rolling swell | big rolling swell |
| 6 ft | rough | rough | rough | rough | rough | rough | big rolling swell | big rolling swell |
"Swell" needs both a long period (8 s+) and gentle steepness; a 4 ft+ sea that isn't gentle swell reads as rough no matter the period.
How it feeds the Blue Wake Score
The score uses the same height ÷ period² steepness behind this grid: steep, short-period water costs points that long-period water of the same height keeps.
The height thresholds flex with the boat you pick — 2 ft of short chop rattles a runabout and barely registers on a 40-footer.
At 4 ft seas or 22 kt sustained wind — the Great Lakes Small Craft Advisory criteria — the score is capped into Blown Out regardless of everything else.
The full scoring model — wind, gusts, direction, hazards, and the five tiers — is on How the Score works.