I assume your talking about a stand-alone unit, Not a marine AC system with de-humid control. And your in coastal S C now and summer? Does the water drain out a hose or in a collecting part of the unit? If the factory manual does not offer any guidance, I would start around 70% on a normal day. With bilge hatches closed, See if it can run and cycle for a day or two. IMO, if it cycles, it is working. If it never cycles off, its like setting your AC to 50° when the door are open on a 100° day,, and it will never drain.
I'm on the gulf. I set mine for 65%, and it seems to keep the cabin nice before I go aboard and start the AC.
