:party-smiley-004:

I appreciate your effort into figuring out how much I burn. I stated that I burned a little over a 1/4 of a tank (perhaps I should have been more specific, as it read on my guage), I actually don't recall how many gallons it took the next time I filled up (I fill up everytime). I have two 72 gallon tanks, and I can guarantee I did not exceed 35 gallons a side (I'm being generous). I'm not saying that my boat is a Prius. My point was the calculation is incorrect. According to the calculation link, My old 18,500lb cruiser would burn the same amount of fuel as my AT.

The numbers on the link provided are very accurate. A 496/502 HO burns about 20-21 GPH at 4000 rpm and 33-35 GPH at wide-open. Mags will burn slightly less.

Soooo....you're saying a 2000lbs 23' boat with a single 496 will burn the same amount of fuel (per engine) as a 9000lb 38' with twin 496's. That makes no sense. If that were true, than, in the auto world, a mustang with a 302 would burn the same amount as an F-150 with the same motor.....

To the OP.

In June I ran my single 502 272 from Orange Beach AL to Destin FL and back on +/- 60 gallons. I believe this trip is around 165-180 miles. Cruising between 3500-4000, 45-50 MPH. The math shows right at 2.75 MGP.

My gauge moves much quicker on the "second half" of the tank. So it's kinda a guess (these are round numbers) that 2/3 of a tank on the gauge equals 60 gallons. 90 gallon tank. I didn't log actual mileage either, but you get the idea.

To a certain extent yes they will burn the same, as boats don't have transmissions, axle ratios, tire sizes, etc.

In a small boat the load would be far less if they were "geared" the same. But, obviously they aren't as we prop our boats to be in the desired rpm range. A 2000 lb boat is going to have a much bigger prop on it. So, a 2000 lb boat with a 30 pitch prop will have a similar load as 9000 lb boat with twins running 22 pitch props(I'm just throwing pitch examples out there). Which means they will burn similar fuel amounts. The difference will be in the speeds.

ok yesterday I had the boat out with a full tank (stopped when I hear gurgling from the vent) ran 24.9 miles and fill the boat back up to till I heard gurgling i took 13.86 gallons of fuel. I ran the boat from 4000 rpm to wot (5000 rpm) a few times for minute each (4) So with a 65 gallon tank I can go 116.77 miles approximately

There you go! That's the best way to figure it out for sure. You could probably stretch it another 40 miles or so(if you had to) by cruising at 3500 rpms. It's just not nearly as fun! :)

Who TF runs a 38' boat with 22" props? Or a 23' boat with a 30" prop? Just give in and admit that this makes no sense....

Did you not read my disclaimer that I just through those pitches out as examples? My point was a smaller, lighter boat will be "geared" differently with a larger prop and therefore experience a similar load compared to a larger boat with smaller props, and in turn burn similar amounts of fuel. The difference will be in the speeds. Or in an example of small single vs big twin, even if they have similar props the load is being split between the two engines on the twin. There will be minor differences in gph because of hull efficiencies but nothing major.

Why don't you give in and admit that you're full of chit. I usually leave posts like this alone as I don't really care. But when someone claims their twin 500hp boat gets 8mpg it's so ridiculous that I feel I have to so no one believes him. Then they correct themselves and state they may have been off but they know the burned 70 gallons max on a 280 mile trip. Still full of chit. You seriously expect people to believe that your engines burn less than 9 gph and your boat gets 4 mpg at 4000 rpm?

I was worried about hijacking this thread but the OP put up his own numbers. Which, by the way, add up mathematically.