54 percent calm and 46 percent rough. That comes from our own survey of 643 crossings reported by 348 travellers, and the 95 percent confidence interval on the rough figure runs from 42 to 50 percent, which is tight enough to publish. The mean rating was 4.86 out of 10 on a Drake Lake to Drake Shake scale, with a median of 5.
The dataset splits by direction too. Southbound came back rough 41 percent of the time and northbound 50 percent, so the return leg runs somewhat harder.
Two caveats we'd rather state than hide. The percentages divide by the 635 crossings travellers labelled Lake or Shake, and the mean rating divides by the 641 they scored, because some people left a leg blank. And the data does not support any month-by-month ranking. The months are unevenly sampled and their intervals overlap, so November looking rougher than December isn't an established difference.
This is first-party data collected from travellers rather than an operator estimate, which is why we're willing to put numbers on it.