Do these fuel burn numbers sound right for a 454 powered 89 3100 open?

[rose_surfer]

I'm prepping for a long trip and want to plan fuel usage. I had thought I should be getting around 1 mpg at cruise. However I think I'm getting far less.

The boat has a very old analog floscan on one of the engines. It reads about 3-4 gph at 6 kts - basically hull speed just above idle, and about 18 gph at 22kts (about 31-3200 rpm). Doubling that for the two engines, that means I'm only getting about 0.7 stature mpg, and dropping down to hull speed seems to, if anything, make it worse.

Do these numbers sound right for carb'd 454's or is it likely my floscan is reading high?

[ReelMagic]

Sounds about right..... I had a 1997 31' Open w/454 Crusaders and burned about 32 GPH @ 3300 (23 knots).... That's about .7 MPG. I now own a 2003 38' Open w/450hp Cummins and its much better.... Burn is approx. 28 GPH @ 24 knots (.85 MPG) for a boat that is significantly larger......... Happy w/38' OPen

[YOLO]

I agree, sound about right. Those gassers are thirsty!

[Lured Away]

I had a 1988 with big block crusaders and had installed a Twinscan. If I recall the secondaries opened up right above 3250rpm (you can hear it when they open) and it would jump up to 15-16 GPH  per motor.  If you can keep out of the secondaries around 3200rpm it burned 11-13 GPH and ran 21-22kts.  I tracked the fuel burn over the years and was pretty consistent.  

[rose_surfer]

Interesting that's about what I hoped for. But I'm reading about 17-18gph on the port motor at 3100 rpm and 21 kts (it's an older analog floscan only on one engine). I also hear my secondaries open earlier - maybe 2900 or so. I wonder if I need a carb adjustment.

[rkaufman]

I have a 1995 and the dash gas gauges are pretty worthless. Interestingly, there are gauges on the top of each tank that are spot on.