power estimation

Discussion in 'Propulsion' started by sobo, Oct 30, 2010.

  1. sobo
    Joined: Oct 2010
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    Location: malaysia

    sobo Junior Member

    hi there

    I got a question to ask regarding my project. i need to determine speed of a boat where the total resistance and the type of engine used are known. This boat is using the outboard engine which the detail as in the link below

    http://www.mercurymarine.com/engines/engine-tests/boat-house-bulletin/?ID=437&96251.72120954655

    For your information, the only detail that i have currently is the RPM of the engine that they used during voyage. i need to find the speed of that boat at that particular RPM.

    Once i obtain the effective power of that boat, i can determine the require speed in the maxsurf software.

    my question is,
    1) how can i obtain the effective power when i don't even know the efficiency of the shaft,brake,etc..?
    2) as stated in the engine specification, the horsepower is 50. Does that mean 50 hp is engine power?or brake power?

    I do hope anyone can help me with this kind of problem. Thank you.
    will appreciate your kindness
     
  2. terhohalme
    Joined: Jun 2003
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    terhohalme BEng Boat Technology

    In estimations, you can use 50 % of installed power as an effective power.
     
  3. sobo
    Joined: Oct 2010
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    sobo Junior Member

  4. sobo
    Joined: Oct 2010
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    sobo Junior Member

    and 1 more thing
    from the equation P = R x V
    effective power means the maximum speed that the boat can run for that specific power right?

    how can i determine the speed that they used at certain RPM of the engine which is specified?
     
  5. terhohalme
    Joined: Jun 2003
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    terhohalme BEng Boat Technology

    Effective power is what is needed to tow the boat at specific speed. Resistance will also chance by speed. How do you know the total resistance? Savitsky?

    For the Power/RPM you need the engine curves.

    Somehow your thinking is too complicated for me and my English...
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Outboards are rated at propeller HP. You don't need to do any calculations for transmission loss, etc.
     
  7. sobo
    Joined: Oct 2010
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    sobo Junior Member

    thanks for the info sir
    really appreciate your help..

    thank you
     
  8. Booker
    Joined: Jun 2007
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    Booker Naval Architect

    I'm interested in the reference you have for this statement.

    Thanks,

    MPB
     

  9. sobo
    Joined: Oct 2010
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    Location: malaysia

    sobo Junior Member

    Thanks for your advise.really appreciate it.
     
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