which hull produce lower fuel consumption?

Discussion in 'Outboards' started by sobo, Mar 27, 2011.

  1. sobo
    Joined: Oct 2010
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    sobo Junior Member

    Hi everyone

    I have a situation here. Can someone share with me on how can i calculate fuel consumption of a boat?.

    I have designing two different boats' hull form which using the same outboard engine. how can i calculate its fuel consumption at design speed so that I can compare which hull produce lower fuel consumption.

    Thank you for your kindness
     
  2. PAR
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    PAR Yacht Designer/Builder

    And you say you've "designed" these two hulls, but can't tell which might be more efficient under power? So, how far along in the design process are you?
     
  3. sobo
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    sobo Junior Member

    sorry for misunderstanding
    actually, i am investigating a boat which currently operated. From my naked eyes, I found that the hull design produced a lot of resistance. Therefore, i am designing a new hull form.
    My problem would be how can I measure the fuel consumption of the new boat so that I can make a comparison on how much fuel can the owner saved by using my hull design.
     
  4. sobo
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    sobo Junior Member

    after modelling both design in Maxsurf, i can clearly said that the new hull form produced lower resistance at design speed.

    for now, i want to know the VALUE of fuel consumption that the owner can saved.

    maybe by some calculation or anything.

    thanks
     
  5. michael pierzga
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    michael pierzga Senior Member

  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    It depends on the design parameters. For example, a planing hull will have less fuel consumption at slightly above planing speed than slightly below. You are not providing enough information for a relevant answer.
     
  7. War Whoop
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    War Whoop Senior Member

    Fuel consumption?? A properly designed cat is what you are looking for.
     
  8. sobo
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    sobo Junior Member

    thanks for your answer
    both designs are catamaran type which have the same Volume Displaced, LOA, Breadth. It only differ by hull shape.

    hope that the info is enough. feel free to ask me if i did not provide enough info.

    thanks
     
  9. sobo
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    sobo Junior Member

    hi,
    thanks for answering my question. but, could you elaborate more on your answer. i can't understand what you mean by properly designed cat
     
  10. daiquiri
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    daiquiri Engineering and Design

    Well, to be honest I don't see any useful info until now. We only know by now that both boats are catamarans, that they are powered by an outboard and that one will consume more than the other. Period.

    Anyways, if you have calculated the drag and effective power required by the two boats (for a desired cruise or max speed), one way of calculating their fuel consumption is to make a calculation (actually to estimate, and sometimes even to guesstimate) of power efficiencies of the whole propulsion chain - starting from the propeller (corrected for the wake effects), through the shaft, bearings, gears, all the way to the motor.
    In this way you'll obtain the engine break power (Pb) necessary to obtain the required effective power (Pe). Then you have to divide the Pb by the thermal efficiency of your engine (which will depend on the engine type), in order to get the power input by the fuel. then divide this last number by the specific energy content of the fuel used (http://en.wikipedia.org/wiki/Fuel_efficiency#Energy_content_of_fuel) and you will get the required fuel flow.

    Or use the engine performance data supplied by the manufacturer.

    And don't forget to always use consistent units!

    Cheers
     
  11. sobo
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    sobo Junior Member

    thanks daiquiri for your answer

    that would be the answer i am looking for.thank you very much.
    sorry for not providing good enough information.

    fyi,actually,i am already obtained the effective power of my boat.

    thank mate!
     
  12. BATAAN
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    BATAAN Senior Member

    Long, skinny, shallow, light with lots of power.
     
  13. daiquiri
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    daiquiri Engineering and Design

    Why lots of power?
     
  14. BATAAN
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    BATAAN Senior Member

    Enough power to overcome resistance of hull and weather and give designed performance under all conditions. Also, is good if 70% throttle gives cruising speed as engine is not so stressed. Of course everything is a trade-off and soon becomes all engine and tanks and gets too heavy if not careful. WW2 S-Boote is great example of a very fast highly powered design with useful load and all-weather use. 40+ knots.
     

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  15. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Ah, ok then.
    So not "a lots of power" but just the power sufficient to ensure the desired seaworthiness and performance in a seaway. ;)

    Cheers
     
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