Hi Paul, welcome aboard
I'm not too knowledgeable (bottom end of the learning curve) but we have a 30' Sundowner Tug as well, so I'll give you what information I have.
The previous owner (PO), who wasn't very diligent updating his maintenance log as his health deteriorated, put in a 100hp Yanmar 4JH2-UTE engine with a Yanmar/Hurth KM4A transmission...not sure of the gear ratio...will check next time down at the boat. The propeller is three blade 17x15.
We normally cruise at about 7 knots at 2700rpm, or a bit past where the turbo kicks in. Crunching the numbers after our first year showed we burned 1.2 gallons an hour overall.
The PO took good notes on a trip from Vancouver to Kitimat, running between 2900 and 3050rpm, and wrote that Badger used 2.2 gallons an hour overall.
Let me know if you need more clarification or have any other questions,