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  1. #1
    Seaman Apprentice
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    Default 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. #2
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    Default 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. #3
    Petty Officer 1st Class
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    Default 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.

  4. #4
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    Default Re: Outboard Gas MIleage

    Quote 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.

  5. #5
    Petty Officer 2nd Class
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    Default 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....

  6. #6
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    Default 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.

  7. #7
    Chief Petty Officer
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    Default Re: Outboard Gas MIleage

    Quote 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.

  8. #8
    Seaman Apprentice
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    Default Re: Outboard Gas MIleage

    Quote 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

  9. #9
    Fleet Admiral Mark42's Avatar
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    Default 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.
    1985 Bayliner 1600 Capri Cuddy, 1965 MFG Niagara Custom. >> MFG Video<<. >> MFG Project<< >>Bayliner Hard Top Project<< >>Bayliner Repower Project<<


  10. #10
    Seaman Apprentice
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    Default 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

  11. #11
    Seaman Apprentice
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    Default Re: Outboard Gas MIleage

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

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