Resistance prediction for a large B/T

Discussion in 'Boat Design' started by pavel915, Sep 26, 2010.

  1. Leo Lazauskas
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    Leo Lazauskas Senior Member

    For the non-English speakers here...

    "Michell" is not pronounced like the French "Michelle". The first syllable rhymes with "rich".

    "Froude" rhymes with "dude", not with "crowd".

    Don't make these simple mistakes, or people will laugh behind your back at hydrodynamics parties. :)

    Leo.
     
  2. baeckmo
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    baeckmo Hydrodynamics

    The referrence posted by Olaf is the one I had in mind, and yes, the limit of application is 1<Fnd<2. At Fnd=1, the writers mention an average difference measured/calculated of 6.0 %, and increasing in the low Fnd range.

    Extrapolating down to Fnd=0.8 is questionable, of course. If that is your only way, however, then you should plot the coefficients (A1 to A27) versus Fnd. Then apply a curve-fitting function to each and see if they change smoothly in the low Fnd range. If so, they may be extrapolated down to Fnd=0.8. Of course this is increasing the the mean fault range, but if no other way is available, you have to use whatever information you can get, and be aware of the risk level. That is the essence of engineering, irl!

    Recalculating for another size is of course conducted "as usual"; separate the friction area and its friction losses from the rest of the losses, recalculate for a new Reynolds no, with a new friction coefficient. The recalculate friction with the new wetted surface and speed and recombine with the residual resistance. In this range though, the real Cf-values are quite flat and the major influence comes from the relative "unsmoothness" of the surface, but that should be simple piece of cake for a NA.
     
  3. pavel915
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    pavel915 Senior Member

    Baeckmo,
    Model no 4668 is of which series? How can i find information regarding this? I need any model test data which is close to my boat, then I will have a smell that what should be the characteristic of the resistance curve of my boat.
     
  4. baeckmo
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    baeckmo Hydrodynamics

    "Resistance tests of a systematic series of planing hull forms",

    E.P. Clement, D. L. Blount, SNAME 1963.
     

  5. pavel915
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    pavel915 Senior Member

    Baeckmo,
    I googled a lot,,,but did not get that paper.
    It is not available free?
     
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