Resistance Prediction Methods Help!!

Discussion in 'Hydrodynamics and Aerodynamics' started by GeorgeMarEng, May 10, 2012.

  1. GeorgeMarEng
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    GeorgeMarEng Junior Member

    I was just wondering if anyone could give me and idea of (in nutshell) the limitations and appropriate vessel types for the following resistance prediction algorithms, as i do not have access to the relevant references to find out these things
    Gerritsma et al 1981

    Gerritsma et al 1996

    Savitsky AND Brown (already have a general idea about the standalone savitsky method..i think!!)

    Many Thanks
     
  2. Alik
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    Alik Senior Member

    Molland A. 'Ship Resistance and Propulsion: Practical Estimation of Ship Propulsive Power'
     
  3. ldigas
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    ldigas Senior Member

    Quite expensive!

    Is there anything worthwhile inside or is it just the usual boilerplate text found in any other book dealing with hull resistance?

    Judging from the TOC on Amazon, only the last chapters seem they could contain some newer findings.
     
  4. daiquiri
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    daiquiri Engineering and Design

  5. GeorgeMarEng
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    GeorgeMarEng Junior Member

    Thanks for the book reference, but unfortunately i dont have access to a library or that kind of cash at the moment! Are there any internet links with reliable info on just the basics of these methods, or someone that can breifly state the limitations (Fr, Cb, LBT, etc) and hull forms appropriate.

    Thanks
     
  6. GeorgeMarEng
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    GeorgeMarEng Junior Member

    Thats excellent! Thanks so much, and just on the off chance do you know if savitsky and 'savitsky and brown' method are very similar?

    Cheers
     
  7. daiquiri
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    daiquiri Engineering and Design

    Here is the 1992 paper by Gerritsma et al.: http://www.hiswasymposium.com/asset...17th - 2002/Gerritsma@hiswasymposium-2002.pdf
     
  8. daiquiri
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    daiquiri Engineering and Design

    Savitsky & Brown work is an extension of the original Savitsky's work (which was for prismatic hulls in calm water) to prismatic and warped hulls in seaway, together with a description of a Mercier-Savitsky method for evaluation of resistance in the pre-planing range. The paper can be found here: http://www.boatdesign.net/Forums/at...638152-savitskys-papers-savitsky_brown_76.pdf
    Cheers
     
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  9. GeorgeMarEng
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    GeorgeMarEng Junior Member

    Thats fantastic thanks a bunch!
     
  10. ldigas
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    ldigas Senior Member

    I did my thesis on methods of small craft resistance and their verification. Just to note - from what I recall (going from memory here, so give me some rope) of that Brown paper - one should be careful with those terms dealing with flaps, and right somewhere near the end - terms for vertical accelerations.

    Don't remember what exactly was weird with the flap equations, but the acceleration terms were giving some weird values. Too big, if memory serves.

    Has anyone else done any comparisons of the above, that they could put here to put me wrong?
     
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  11. Alik
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    Alik Senior Member

    Knowledge is not expensive... Book is quite good; it presents coefficients for many methods so is usable.
     
  12. daiquiri
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    daiquiri Engineering and Design

    I'm sorry, can't help you there. Perhaps someone else will jump in and give an answer...
     
  13. J Feenstra
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    J Feenstra Junior Member

    hello all!
    The problems with the accelerations method were that it was derived from an statistical study, by Fridsma at the Davidson, long long LONG time ago. Fridsma had to do the study in two parts, I think it was because his first assumption regarding the test were wrong. Doesn’t really matter for this topic I believe.
    Savitsky and Brown derived a set of easy to use formula’s for the prediction of acceleration, based upon the test results of Fridsma. So the limitations were that of the scope of the test characteristics of Fridsma. In the study of Savitsky and Brown, they claim a error margin of 0,2g, that is if the design was to lay within the set boundaries.
    I hope this is a suitable answer for youre question regarding Accelerations, don’t know the weirdness of the flap predication.
    l
     

  14. khabiran
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    khabiran Junior Member

    Hi every body

    Also it's noticeable that could find last method during ITTC2008 and 2011...in Rio..
    BR
     
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