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Outboard Gas MIleage

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  • Outboard Gas MIleage

    Hey guys, I have recently got my boat fixed and only gone out on it twice since. I am trying to get an idea of how far I can go, and safely return without running out of fuel lol. Is there anyway to get a better estimate than just trial and error? Its a 1989 48hp Johnson, #J48ESLCER. I read somewhere online that for most two stroke motors you can just divide the HP by 10 and get a rough estimate of its GPH.


  • #2
    Re: Outboard Gas MIleage

    But it is (@ WOT, anyway). Wait, you said mpg ... no way. It's gph (gallons per hour)!!! and 4.8 gph is about right.
    Jim

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    • #3
      Re: Outboard Gas MIleage

      I think the formula is HP/10 = Gallons in 1 Hour, so a 40hp will burn roughly 4 gallons in 1 hour at wide open throttle. Your weight and hull design will affect this figure too. Lower throttle settings may give better mileage, as long as you are up on plane and the timing at its most advanced position.

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      • #4
        Re: Outboard Gas MIleage

        Originally posted by wilde1j View Post
        But it is (@ WOT, anyway). Wait, you said mpg ... no way. It's gph (gallons per hour)!!! and 4.8 gph is about right.
        lol sorry Jim your absolutely right. GPH! I will edit that now. Thank you both that helps a alot.

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        • #5
          Re: Outboard Gas MIleage

          after you get it figured out best too use a 1/3 fuel rule.Freshwater lakes are not too bad but several years ago I had a 225 on a 22' boat,I went out about 20 miles in gulf , nice calms seas an no rain in forcast.Used about 17 gal. fuel(60 gal tank.A thick fog bank rolled in on us an had too drive at a reduced speed coming back in,couldn't even see the bow of the boat, almost ran out of gas before I got back too the ramp. motors have a sweet spot for the best fuel useage....

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          • #6
            Re: Outboard Gas MIleage

            Yamaha has a site called: Yamaha Outboard Performance Bulletins, you plug in your boat, motor, HP, etc. and it gives you MPG, GPH, MPH on a chart for the rig at all RPM's and speeds. This may help you get an idea about your motor's fuel mileage, performance, best cruise speed/RPM.

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            • #7
              Re: Outboard Gas MIleage

              Originally posted by blimp View Post
              I think the formula is HP/10 = Gallons in 1 Hour, so a 40hp will burn roughly 4 gallons in 1 hour at wide open throttle. Your weight and hull design will affect this figure too. Lower throttle settings may give better mileage, as long as you are up on plane and the timing at its most advanced position.
              Acually, weight and hull design -theoretically, and in my experience - do not affect the GPH at all at WOT. GPH is simply a function of how much gas it takes to produce the horsepower. It will be the same with a slow boat or a fast boat.

              What the load and hull affect is how fast you're going at WOT, and therefore MPG. Although the GPH will be the same, a lighter, more efficient hull will go faster and therefore further for the same amount of gas burned at WOT. MPG, not GPH is better.

              It's always more efficient to go at a planing speed below WOT, but again, for any given RPM's, a more efficient or lighter hull won't give you a better GPH, but will probably give you a better MPG.

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              • #8
                Re: Outboard Gas MIleage

                Originally posted by d.boat View Post
                Acually, weight and hull design -theoretically, and in my experience - do not affect the GPH at all at WOT. GPH is simply a function of how much gas it takes to produce the horsepower. It will be the same with a slow boat or a fast boat.

                What the load and hull affect is how fast you're going at WOT, and therefore MPG. Although the GPH will be the same, a lighter, more efficient hull will go faster and therefore further for the same amount of gas burned at WOT. MPG, not GPH is better.

                It's always more efficient to go at a planing speed below WOT, but again, for any given RPM's, a more efficient or lighter hull won't give you a better GPH, but will probably give you a better MPG.
                Major give away that I'm a new boater, but what the heck is WOT. I have seen it referenced many times! lol

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                • #9
                  Re: Outboard Gas MIleage

                  The 40 Johnson on my 14 ft runabout gets about 7 mpg running at about 20-25 mph. Because I have charts of the area I boat in, its easy to determine distance traveled and fuel consumed.
                  sigpic 1985 Bayliner 1600 Capri Cuddy, 1965 MFG Niagara Custom. >> MFG Video<<. >> MFG Project<< >>Bayliner Hard Top Project<< >>Bayliner Repower Project<<

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                  • #10
                    Re: Outboard Gas MIleage

                    Major give away that I'm a new boater, but what the heck is WOT. I have seen it referenced many times! lol
                    Reply With Quote
                    WOT= Wide Open Throttle

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                    • #11
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                      Re: Outboard Gas MIleage

                      Originally posted by swannytheswan View Post
                      WOT= Wide Open Throttle
                      Thanks so much Swanny!

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