Does your setup let you identify and select from shore points, or do
you have to somehow first configure the arch unit?

When I get to where I need wifi it's a simple matter of surfing to the arch
unit's web configuration page, selecting a site survey and picking an SSID.
Works pretty well.

And, if you tuned the power, what power is available in these units?

Turned down the radio's transmission mW setting until it just barely covers
more than the cockpit region of the boat. Ended up being about 9mW.

And, speaking of power, how did you power them? Are they in the same
place, or is the bridge in the arch and the AP somewhere below?

One unit's in the arch, the other's in a cabinet belowdecks. Both are
powered off the boat's 12vdc. They're on the same breaker so I can cut
power to them when they're not needed. I just ran 14ga wire directly to
them instead of screwing around with power-over-ethernet.

So, back to the story, while it's a great deal more expensive than a
simple USB dongle, if you *really* want wifi at anchor or in the
marina, do it as Bill has done. Get a bridge, connected to a high-gain
antenna, weatherproof-enclose it, mount it as high as you can get it (a
sailboat mast is pretty high!). The ethernet connection out of that
bridge is your gateway to the internet. Connect it to an access point
instead of to your computer, and you can use yours, and your mates,
theirs, wirelessly.

An important point is to keep the radio that's talking to the shore as close
as possible to the antenna. There's no sense in having this sort of setup
if you're going to just go and lose gain by running a long length of coax.
I've got about 30" of cabling total from the antenna to the router mounted
inside the arch. Then I run wired ethernet to the second router belowdecks.
Wired ethernet can run upward of 100 meters, a much better deal than RF coax
dB loss.

The only downside is if you're really close to the shore antenna the signal
can fluctuate with boat rocking motion. The further you're away from the
shore the 'spread' from the antenna will cover a larger area and be less
affected by wave motion. Think of it as a donut shape radiating outward,
with a vertical angle of typically around 15 degrees. Close in that pattern
is "too tight" with something like only 7 feet of vertical coverage. But
get a bit further out and the end coverage area spans a much taller
distance.

The single biggest advantage to this is all the admiral has to do is fire up
her laptop and use the 'boat' ssid. No extra config hassles on her machine.
This alone is worth the effort. Sure, I have to manually select the shore
ssid but that's a trivial process.

-Bill Kearney