We have a Nordhavn.
This isn't our boat but its same model.
http://youtu.be/Ms7RSaR5Znc
Has a Lugger (John Deere) six cylinder diesel.
Non-turbo non-computer controlled. At 7 kts it burns less then 2 gals an hours. We carry 920 gallons.
at 6knots we can go 3400 NM.
Lots of Nordhavns out your way.