Hello again windtraveler. I have the Yanmar 4JH2-DTE 75 hp turbo in my Nauticat. It is the mechanics opinion that the turbo (seals etc..) - and lack of use by the previous owner - is the reason for my oil burning. Although turbos are more common than they used to be I'd not have one for your planned useage though. I think the non-turbo version of mine is 56 or so hp which might be fine for you (I'm 18,000lbs) and it Will Push me over hull speed at full throttle.
Wickford/Narragansett Bay RI