We first used Badger (30' Sundowner Tug) in early March this year and filled up the tanks yesterday, so I decided to crunch the numbers.
We put 178 hours on Badger's 100hp 4JH2-UTE Yanmar engine, and after yesterdays fill up to put the tanks back to full we used 1022 litres, or 268 gallons of diesel. So the way I figure it (always a mathematically shaky proposition) we averaged 1.5 gallons per hour overall. This includes farting around after crab traps, anchoring, docking, and our 7 knot or so cruising speed.
The PO installed a third smaller fuel tank, so we can hold 140 gallons. Yesterdays fill up was our largest at 92 gallons, which left 1/3 in the tanks. After a bit of head scratching, I figure that gives us a range of about 425 miles on 2/3 of the tanks.
Good to know