Diesel VS 4 stroke outboard fuel consumption

Discussion in 'Propulsion' started by DennisRB, Jul 20, 2010.

  1. goodwilltoall
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    goodwilltoall Senior Member

    Apex,

    At the beginning of the thread it was mentioned "fuel consumption".

    That's measured by how much fuel you use by lets say "gallons per nautical mile".

    You probably are right when you measure by total lifetime costs but just want to know how much per gallon of diesel vs. per gallon of gasoline you get.
    Old presumptions about so many btu per gallon might not apply as newer 4strokes have definitely improved technology for what is hoped is dramatic fuel savings.
     
  2. CatBuilder

    CatBuilder Previous Member

    Although Apex1 (as usual) makes excellent points, I have owned a few Yanmar inboards and a single Honda 4 stroke outboard. I was amazed at the fuel efficiency of the Honda. It did, indeed rival the Yanmar diesel in GPH.

    I was unaware that gas/petrol was less expensive than diesel around the globe. I thought that reversal was a global trend. Good information to know. I haven't traveled out of the country in several years.

    EDIT: I wanted to add that I'm only talking about auxiliary engines, as I'm a sailing type.
     
  3. jonr
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    jonr Senior Member

    This is a good reference - it also shows how much difference the specific engine can make (a poor diesel can be close to a good gas engine).

    http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

    I second what CDK said about temperature. You can also select props to get an fully open throttle plate at your normal cruise speed (to minimize pumping losses and maximize compression pressure).
     
  4. WestVanHan
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    WestVanHan Not a Senior Member

    So you had a boat with a Yan diesel,got rid of it and mounted a Honda outboard that got the same gph.

    I can see this happening on a small sailboat with a worn out old diesel (reason it was replaced?) with minimal hp then being replaced with a new technology outboard but not on any other vessel.

    Sounds interesting,please elaborate.
     
  5. CDK
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    CDK retired engineer

    First of all, I am not in the habit of repeating statements I came across, but do my own thinking, calculating and estimating.
    Secondly, I phrased it not the way you did.

    (1) Diesel fuel contains more energy than gasoline, both by volume and weight.
    (2) An internal combustion engine works more efficiently when the compression ratio is high and (3) a high operating temperature is allowed.
    (4) Because the yield from a barrel of crude oil is better, diesel fuel/heating oil is cheaper.

    These 4 factors result in covering 30-50% more distance per dollar, pound or euro.

    30-50% is not very accurate, but taxation in various countries makes it difficult to narrow it down. My personal experience when switching from gasoline to heating oil was that fuel costs dropped from 1,50 euro per mile to less than 0,35, so it is better to leave taxation out of the equation.
     
  6. Pierre R
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    Pierre R Senior Member

    The old standby rule was gasolene gives 10hp per gallon per hour and diesel gives 16. Now both have increased a bit but the difference is still about the same. One thing to consider, smaller diesels are not as efficient as larger diesels when it comes to spacific fuel consumption per hp. The difference can but 25% on a small diesel vs a larger diesel. The same is not true for a gasolene engine so outboards are not a bad option against a small diesel.

    One of the biggest things to consider is the real number of hours per year the motor will be used. Diesels do not like to sit nor do they tolerate abuse like a gas engine. If you are not going to use the boat all that much as in local boating vs long distance travel then an outboard can indeed surpass a diesel in overall economy.

    I have seen lots of diesel engines rebuilt or with serious problems with less than 1500 hours on them due to light use in a marine environment. At the same time I have seen outboards go for years on light useage with little or no maintenance.

    Generally speaking if you are going to travel with the boat an inboard diesel is hard to beat. If you only do weekends a couple of hours with the boat then the outboard is likely to win.
     
  7. FAST FRED
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    FAST FRED Senior Member

    And for folks that stop boating when the water gets hard , the Diesel has a long expensive time consuming regime to be mothballed.

    The outboard is 1/ 10 the work or expense..

    FF
     
  8. CatBuilder

    CatBuilder Previous Member

    Another thing I like about outboards as a sailor, is that they retract, allowing greater sailing performance. Also, you can upgrade to the next best greatest fuel source in a very simple way someday.
     
  9. jonr
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    jonr Senior Member

    Suzuki sells some outboards that can run on kerosene. Might be cost effective in some areas.
     
  10. goodwilltoall
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    goodwilltoall Senior Member

    In previous post I made mistake. You can not get same reduction gears, tranny, propeller with inboard 15hp diesel and 15hp gasoline outboard.

    The Honda GX series engines run at 3600rpm and so do the Kubota 15Hp.
    Now if you mounted the Honda inboard you might have a head to head comparison. Wouldnt be the route I would take, but those GX series Honda's have extreme reliability and some have run for over 10,000 hrs, some I know have 5000 hrs.

    Research was made into the Lister 6hp knockoffs built in India for generating electricity. Listers are known to be fuel mizers and very long lived (one was reported to have worked 17 years nonstop), they are very heavy (about 400lbs.) and operate at below 1000rpm and have pleasant sound as they run.
    This engine/generator was compared to a Honda EU2000.

    Both produced the same amount of KWH per gallon with in just fractions.
    Thier are variables involved, but this was done as a quick observation.
     
  11. WestVanHan
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    WestVanHan Not a Senior Member

    So now we're into gensets instead of power? Ok......


    Why not compare it to a modern diesel instead of a knock off of a 90 year old design???????.

    Here's a couple gen sets I'm familiar with cut paste from web site specs:

    Honda 4000:
    MAXIMUM CONTINUOUS AC OUTPUT (WATTS) 2600
    RATED FUEL CONSUMPTION (LITRES / HOUR) 1.68

    Kubota 7000 watt at 1/2 load,so 3250 watts:
    Prime Output (W) 6500
    Fuel Consumption at 1/2 Load L/h 1.7


    So the diesel is putting out 25% (3250/2600) more power for that 1.7 litres an hour AND it's not even running at peak load.

    Kubota no longer makes the smaller ones so consider that this one is operating not as efficiently as it could be.Compare the loading with consumption:
    at Full Load L/h 2.6
    at 3/4 Load L/h 2.1
    at 1/2 Load L/h 1.7

    At 3250 watts it's using 1.7 litres an hour (3250/1700)=1.9 watt/hrs per ml.
    At 6500 watts using 2.6 litres an hour (6500/2600)= 2.5 watt/hrs per ml.
    which is a 31% improvement.

    Taking this to the gas:

    The gas Honda gets 1.5 watt/hrs (2600/1680) per ml of gas.
    The diesel Kubota gets 2.5 watt/hrs per ml of diesel....... 66% more watt/hrs than the GAS Honda.

    Horses for courses,but enough of this silly BS about gas being as or more efficient than diesel.

    Enough.




    http://www.kubotaengine.com/products/gl/gl7000.html
    http://www.honda.ca/HPower/Models/Specifications?Type=Generators&Series=Inverter&Model=EU3000iC&L=E
     
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  12. CDK
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    CDK retired engineer

    Interesting to see that the Honda 4000 puts out 2600 watts, which is equal to 2235 kilocalories. It consumes 1.68 liters of gasoline to do that, which contains approx. 14000 Kcal.

    So the overall efficiency of this popular generator is 16% !!
     
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  13. CatBuilder

    CatBuilder Previous Member

    That's not the popular Honda. The popular one is a Honda eu2000i.
     
  14. CatBuilder

    CatBuilder Previous Member

    According to the link, the eu2000 puts out 1600 watts continuous and does so for 7 hours on a gallon of gas.


    campinglife.com/output.cfm?ID=1112113
     

  15. WestVanHan
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    WestVanHan Not a Senior Member

    Odd.....Honda says quite the opposite on their website:

    AC Output 120V 2000W max. (16.7A) 1600W rated (13.3A)
    APPROXIMATE RUNNING TIME / TANKFUL (HRS.) 4.0**
    RATED FUEL CONSUMPTION (LITRES / HOUR) 0.97**
    **** at max. rated output (continuous) in Watts.

    So doing the arithmetic...
    1600 watts divided by .97 litres (970 ml) an hour equates to 1.65 watts per ml of gas which is slightly better economy (vs 1.5) than the "unpopular" 4000 watt version.

    Which is still substantially worse than the diesel's 2.5 watts per ml.


    Please-no more- I'm tired of this.


    http://www.honda.ca/HPower/Models/Specifications?Type=Generators&Series=Inverter&Model=EU2000iCM&L=E
     
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