Boyd, again, no oil expert here, but oil weight aside, I've seen a lot of people on the boat forums expressing concern over the lowering of zinc additives in many of the oils traditionally popular in the boats. This is something that has happened in the last few years. For folks with flat tappet cams like you and me, the consensus is that it is something we don't want to go without. Many have mentioned Chevron Delo, Royal Purple or Valvoline VR1 as brands that have maintained acceptable ZDDP levels for our motors. I know there are others, but I can't call them up right now. If straight 30 weight oil works for you, great. But check those ZDDP levels, too.
Previous: 1993 Prostar 205
Red 1998 Ski Nautique, PCM GT40, 310 hp, , Acme 4 blade, Perfect Pass SG/Zbox.
Be kind. Have fun.