Cal,

Besides your other calculations, I would think about the useful life of
the diesel (or at least the time to a rebuild). An early rebuild will
cost a lot more than the likely fuel savings based on engine choice.
Modern turbocharged high-RPM lightweight diesels share little in common
with traditional shipboard engines (except the fuel).

Look at the following link to David Pascoe's Boat Survey site (this
whole site is a pretty depressing commentary on boat quality these days
- you might want to have a few drinks before visiting). I understand
that some surveyors believe his opinions are overly alarmist and
negative.

http://www.yachtsurvey.com/GasNdiesel.htm

One of his opinions is that you ideally want a diesel that has a CUI/HP
(CubicInchDisplacement divided by HorsePower ) of less than 0.7. A
ratio over 1.0 is not good.

He agrees with some others posters that you can get dangerous carbon
buildup if you don't run your diesel at high enough RPM's. It can
lead to catastrophic engine failure (that sounds like fun!)

Also, make sure you get to HEAR your engine at harbor speed and
cruising speed before making a decision. I find some turbochargers
sound like a dentist's drill - others have a less grating pitch. It
also seems some engines are just plain quieter - although it's hard
to compensate for the quality of the engine room insulation.

Carl