estimate the fuel use in early design stage

Discussion in 'Powerboats' started by ikh_one86, Sep 22, 2010.

  1. ikh_one86
    Joined: Aug 2010
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    ikh_one86 New Member

    can i estimate the use of fuel if im only given the power of the ship, the cruising speed, the displacement and type of ship. i have been introduced to the navcad software, but i dont have the software. just want to approach through calculation method.

    tq.
     
  2. WestVanHan
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    WestVanHan Not a Senior Member

    IF you know the hp required at a certain speed and IF you know the rpm and IF it's loaded properly and IF you have the exact engine graphs you can look up the gph and efficiency at that rpm and get an idea.
     
  3. FAST FRED
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    FAST FRED Senior Member

    IF you are just doing the early Mental ************ on a new design, a few rules of thumb will speed the process.

    Any old gas car engine or most outboards will get 10 hp from a gallon of fuel, go computer fuel injection and super modern and proper setup perhaps 14 hp/gph.


    Most old diesels will crank 16 hp , but with enough tech , expense and computers 22hp is advertised by some engine builders. Over 20 running is RARE!

    FF
     
  4. apex1

    apex1 Guest

    You are talking "ship", so I guess we are in the commercial world here.

    Yes you can estimate the consumption roughly.
    The engine will operate at about 85% rated power output at cruising speed, just because thats standard in the merchant fleet and the engines are designed for it.
    Now you need the engines specific consumption from the data sheets. The bigger Diesels come with 190 gram kW/h and less, going up with decreasing swept cyl. volume.

    West,

    we don´t have gph in the maritime world. It is either gram kW/h, or metric tonnes per day. (specific/absolute)
    Because we don´t have any fuel by volume, just by weight.
    Making Freds assumptions moot as well.

    Regards
    Richard
     
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    The 190 kWg/h that Apex quotes are for bigger engines, ie very big! (Bigger than your house)

    The medium to high speed engines are generally in the 200~220gkW/h

    Fuel consumption is simply this:

    (g/kW/h) x MCR/850 = litres per hour

    MCR = max continuous rating of Engine.

    Then divide into amount of litres onboard to give you 'hours', then multiply by the speed = range in nm.
     
  6. apex1

    apex1 Guest

    Thats what I meant, ships, real ships!
     
  7. WestVanHan
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    WestVanHan Not a Senior Member

    Apex thanks I know....I'm assuming when he says "ship" he's not building a huge ship.

    190 gram kW/h with the grenaa........is this at all rpms??
     
  8. yipster
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    yipster designer

    for power boats my understanding was its still common to give gallons a mile
     
  9. apex1

    apex1 Guest

    No,

    this was unfortunately not for the Grenaa, but for the 60.000hp monsters and upwards.

    The Grenaa is about 203 g/kW/h

    And I assume we have one of the many requests from a Malaysian student here, hence my comment on ships, not boats.

    Yipster,
    yes on forums and in marina bars. The professional world does not even know what that would mean.

    Regards
    Richard
     
  10. jehardiman
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    jehardiman Senior Member

    The other thing needed to calculate an overall bunkerage requirement (which is the only reason to estimate fuel use) is the voyage profile.

    Most modern transoceanic ships use multiple distilates. One for nearshore and one for offshore. And then there are the generator and lube oil (which drives a LSD total oil consumption up to ~210+ gm/kW-hr) requirements and the economic considerations of where and when to bunker. So a voyage profile needs to be developed so that all bunkerages can be considered.
     
  11. yipster
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    yipster designer

    so "schoolgirls" learn a thing or two and i see some proffesionals that do know what that means, be reasonable and see were not all talking "ships" here
     

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  12. apex1

    apex1 Guest

    Is there a chance not to be contradicted by you?

    Our business, as all others too, has a crisp clear terminology, worldwide agreed and used by all professionals!

    Consumption is measured by Gram kW/hr, or metric tonnes per day (the latter only in the merchant fleet).

    No miles per gallon, no gallon per mile or whatsoever. Mpg is impossible to measure btw., one can only estimate that under one certain condition, which is never constant.

    Journalists tend to ignore the right terminology and to mix it up with terms used on the road, to make their drivel better consumable by Joe Sixpack. That does not make it valid.

    Regards
    Richard
     
  13. yipster
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    yipster designer

    ok fair enough and you'r rite apex but dont call everybody joe sixpack, schoolgirl or dude when they are not a 62.000hp NA or have other views plz
     
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  14. WestVanHan
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    WestVanHan Not a Senior Member

    Someone needs to chill out....
     

  15. apex1

    apex1 Guest

    You turn nasty mate!
    I did not call anyone here a schoolgirl or Joe sixpack! Nor did I refer to 60.000hp or commercial shipping. And I did not attack anyone for having different views.
    Our maritime world has a clear terminology, no matter talking boats or ships.
    Amateurs may drivel in their terms, they don´t know better, but here we should not talk like backyard car tuners when boats are the subject.

    Thats all, back to topic.
     
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