My 2cyl 20HP Albin diesel will push my 31'6" 6 tons longkeeler at 4.3
knots using one liter per hour at about half max rev in flat water.
That would indicate that you could do the same or better than 3.8x4.3
=
16.3 mil per gallon. 12 galons should give arround 190 nautical miles
if you run the engine at the most economical speed, probably 4-4.5
knots if your bottom and prop are clean.

Peter S/Y Anicula

"Thom Stewart" skrev i en meddelelse
...
Scot,

My 2cylinder Universal (18 hp approx) does 6 knots an hour on a
little
over 1 Quart. At 4/5 knots, if not bucking a tide or a stiff
hedwind,
I'd say you'd need about about 26 quarts or 4 Gals.

What is your motoring range for your boat with the 12 Gal tank?
Should
be in your Sps? I'd say that they gave you a 250 mile cruising range
with power

Ole Thom