I would like to be able to install a wired router on the boat and share
the
internet connection among more than one on-board wired computer. This
would
eliminate USB wireless adapters that connect directly to the computer.

Yes, I do this now in our boat. I have a Linksys WRT54GS with the dd-wrt
firmware loaded on it. It's configured for "wifi client mode" and handles
making the connections to shore sources. To that I have a PC wired. I also
have another access point wired to it providing an on-boat Wifi SSID. Our
laptops connect to this. This way the laptops always connect to the same
SSID. I only have to visit a wireless client status page and make a
connection to the on shore SSID. Works pretty well. I'm about to
permanently install some antennae for it, probably some 8db sticks on
ratcheting marine mounts.

-Bill Kearney