Hi,
As mentioned by RC John, Conformal Coating is perhaps the best way to go if you want to actually protect the PCB. The board should be liberally coated - particularly the ICs - if water gets under the legs it can cause mayhem.
I wonder, though, if this is a bit OTT. I suggest that you splash-proof the case - silicone seal around the edges and the connectors. This should IMHO be OK unless you sink the boat. In that case, get the power off ASAP. If you use proper silicone rather than acrylic sealer, keep it well away from the electronics - the sealant gives off acetic acid which will rot the connections.
Soaked PCBs can be cleaned up quite easily - wash the board thoroughly in clean tap water - liberally rinse it. place the board vertically in a warm place and let it dry naturally. If there is significant residue, use an aqueous board cleanser followed by a suitable rinse agent (try RS or Farnell). Relays are, in my opinion,? probably better replaced as the effects on the contacts, particularly if power has been on them while submersed can be damaging.
Wombat