I've had good luck with USB adapters, and 1.1 is definitely fast
enough for good WiFi service.

USB 1.1 tops out at 12mbps, that's a good bit slower than the usual 34+mbps
connections I'm getting to shore SSIDs using a WRT54G in client mode. That
and by using a 1.1 device on your port you're crippling any other devices to
that same slow speed. Downloading pictures from a camera at 1.1 speeds is
maddeningly slow...

They are claiming
20 ft of total USB length on the web site, plenty long enough for my
boat.

Sure, depending on the boat and your desired position for the computer the
length may be appropriate. But I've found it's best to have as little as
possible connected to a laptop. The last thing you want is a cable getting
tangled and yanking the laptop off the table.

I've had great success this season using a setup with two WRT54GS routers.
One's up inside the radar arch connected to a single 8db omni antenna. It's
then wired via ethernet to another WRT54GS acting as an access point. The
laptops onboard connect to the "boat" ssid and the arch router then handles
connecting them to shore. No cables to the laptops save for a power cord
when they need recharging. This lets me connection mine, my wife's and
anyone else 'nearby' to the access point and share connectivity. I've tuned
the power level on the access point to provide coverage to a very small
area.

Works great. Certainly faster than USB 1.1 and with the added benefit of
requiring nothing extra to let other computers connect through it.

-Bill Kearney