Thomas, you've already been given some good advice and the fresh water one is one that I can attest too. On my new boat, an Ocean Alexander Classico 50, I had the waterline raised to 3" above the waterline with all tanks full. This didn't include the many pounds of stuff that typically finds it way on the boat, but I assumed that the 3" would take care of "stuff" and also am banking on my tanks seldom being full. After owning the boat for the better part of the year, I believe my estimate was the right one. I did see someone say they set their's 8" above the waterline, which seems extreme to me. With that said I believe it's better to err on the high side. BTW, the only reason to push the waterline closer to the real waterline is aesthetics. If you can live with seeing a little extra bottom paint, then don't be too conservative. Gil