Roger Long wrote:
There are solid physical reasons why even the most experience sailors
overestimate wave heights by about 100%.

Roger,
It may be true that some overestimate wave heights by this much, but it
is hardly universal. For moderate waves, I am quite confident in my
estimates. It's really quite simple. If you know the height of your
eye above the water as you sit in the cockpit (for instance, mine is
just a hair over 6') then if the wave top is above the horizon while you
are in the trough, it is over 6', if it doesn't, it is under 6'. By
adjusting for how much it appears to be higher/lower than the horizon,
you can then get a very good estimate for waves up to about twice your
base height. Beyond that, it becomes more difficult and the wave
heights become more of a guesstimate than an estimate as it is difficult
to really tell if it is even with the spreaders or how much above/below
them the waves really are.

Note that using this method, you also have to adjust a bit depending on
the amount of heel and whether you are sitting on the high or low side
of the cockpit.

p.s.
Don't forget that all waves have two heights, the one we write down in
the log and the one we tell about at the bar in the story that begins
"No ****, you won't believe....". Could this be the source of your
assertion that most sailors overestimate by 100%?