If you cut your speed back to no more than about 1.1 x SQRT(LWL), about
7 kts, you can probably get your consumption well below 1 gph. I have
a 30 ton 49 footer with twin 671s. At 1000 RPM we get 7 kts at about
..7 gph, at 1300 RPM 8.5 kts at 1 gph.