So, are you saying that the speedo/tach/depth finder is not working, or nothing on the whole dash? Does it respond to your DESS key? Start/stop? Switches working? Can you drive the boat, but you just don't see the guage display?
Judging from your comment on the price, it sounds like you are talking about just the dash gauges. That part can be purchased for around $430 online (plus shipping). I doubt water is the reason for the problem--you'd have to get a lot of water on the dash for any to get behind the panel and into the electrics and the chances of that only affecting the gauges and not any of the switches are very remote.
The instrument cluster is #6 in the panel. I'd double-check that fuse, and even temporarily replace it with a new one to be sure. Even if that's not the problem, there are a couple of things you can do before you resign yourself that the whole IC is bad. After you check/replace the fuse, you can see if you are getting power to the fuse block. Check to make sure there's not a short in the wires to the IC.
