We've now seen this chart posted approximately 10-12 times in just the
past week for some reason, and seen at least 13 reasons why it's so
generalized that it's of limited applicability. Isn't it sort like the way
the military does business: Measure it with a laser, mark it with a spray
pain can, and cut it with an axe? All the precision in the world doesn't
change the basic fact that on a given day you'll see average-weight people
enjoying sail sizes ranging over a meter or even two meters difference,
and all of them feel they're rigged about right on the average. Given
that, reading whitecaps is close enough. By the time we take into account
personal preference, rider weight and ability, number of cams, sail sizing
technique and accuracy, sail quality and design, sail tuning, wind
quality, water conditions, sailing style (straight-line reaching or
power-robbing maneuvering), what's downwind of you (if it's a 100-foot
drop over an unprotected spillway or another continent, you'd better rig
big enough to sail upwind in the lightest lulls), board and fin size, the
wind out on the water versus the wind in your hand-held meter on shore,
whether the wind should build or decay, and your very reason for being out
there (racing for cash and glory or just having fun), these painstakingly
developed charts are primarily academic exercises.
By the time a sailor is experienced enough to minimize the variation from
even half of these confusion factors, s/he's also experienced enough to
mentally integrate whitecaps to calculate his or own ballpark sail size.
The theoretical 155-pound good sailor can generally throw on a 7.something
if there are no whitecaps, a 6.something if there are a few whitecaps, a
5.something if there are plenty of caps, a 4.something if there are a
whole lot of hefty caps, and a 3.something if the wind is blowing spray
off most of the caps. And if a person is even considering going out in
that much wind, s/he already knows all this.
Given that modern sails work fine over a 2-meter range at the large end
and nearly a 1-meter range at the small end (at least a 20% room for
error), caps are usually close enough for government work.
The charts are nice, and took someone a lot of effort, but we don't sail
on paper; we sail on water, in gusty wind, with a big sheet of plastic in
our hands and a little piece of plastic under our back foot. Don't get
paralyzed by selecting sail size; it costs you too much time where it
counts: out there. Park your van and keep glancing at the water as you get
your wetsuit and board out, find your harness, rub on some sunscreen, fill
the dog's water bowl, shove down some more carbos and water, dig out your
mast and boom and mast base, say hi to your buds, ask seven of them what
size sail they're on, and ignore their answers unless you know how your
sail size usually compares to theirs. By that time your 10 glances at the
water have already told you what to rig anyway, and probably much more
accurately than any chart. Get your ass on the water and hang on to what
you rigged for a while. You'll know within one or two gust/lull cycles if
you're rigged right.
Besides, the wind's gonna change by a meter within 20 minutes. Twice.
KISS (Keep It Simple, Sailor)
Never Leave Wind To Find Wind