Delft Series

Discussion in 'Sailboats' started by DavidG, Jan 10, 2002.

  1. Stephen Ditmore
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    Stephen Ditmore Senior Member

  2. DavidG
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    DavidG Junior Member

    I had another look at Delft recently and set up the spreadsheet as per the 14th Chesapeake paper including a flag indicating if I was outside the tested hull parameters (this was not detailed in the Modern Yacht paper) this now returns more sensible values, though maybe not as sensitive as the Delft 1 & 2 series.
     
  3. ibi
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    ibi Junior Member

    Excellent

    But is there any formula for optimizing LCF position versus Fn? - like the Cp and LCB from Larsson? I am very interested in this.
    And another problem. What about waterplane coefficient? In my opinion in might be as importand as LCF. But it is often neglected.

    Any opinions?
     
  4. DavidG
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    DavidG Junior Member

    ibi,

    Firstly, I agree that LCF "separation" from LCB is important, the only way to analyse this (cost effectively) is to set up a Delft Series spreadsheet and input different LCF locations whilst fixing LCB and Cp, you should then be able to observe the trend.

    I am now coming to the view that Delft 1 & 2 (as in Larsson) is best for fixing Cp and LCB, and that the recent versions of Delft are good for LCF (using the Cp and LCB values from 1 & 2).

    My analysis is that the greater LCF/LCB separation reduces residual drag at hull speed (Fn @ 0.35 - 0.40), however you need to observe the boundaries set up by the parent models.

    Assuming that you are not going for an immersed transom, the LCF position will probably be limited by the practical constraints of creating a fair waterline.

    I think that your comment about waterplane co-efficient, is pretty well determined by all the other factors, i.e. if your section area curve, cp, lcb and lcf are right and you have a fair hull, the additional variable may be one too many to consider, especially when also having to consider the hull when heeled and in a wide range of loading conditions!
     
  5. Stephen Ditmore
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    Stephen Ditmore Senior Member

  6. Miles Turner
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    Miles Turner New Member

    Maybe it's worth adding that in 1993 and earlier, all the Delft models were tested with a standard keel and rudder, which were included in the residuary resistance polynomial. The more recent formulations include separate expressions for appendage residuary resistance.

    This is perhaps important because the Delft standard keel and rudder are not very representative of recent practice. Moreover, for light displacement hulls, the contribution of the appendages to the total residuary resistance is pretty significant, as much as 30% for one of the earlier Delft models that I looked at.

    So I concluded that the more recent polynomials should be prefered, unless your keel is like the Delft standard one, or the displacement is so large that the appendage residuary resistance is negligible.
     
  7. ibi
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    ibi Junior Member

    I have no access to the recent Delft series polynomial coefficients. Could anyone send them to me?
    I think, that they are public domain - they were presented in public. So there should be no problems with the copyright.

    Thank You!
     
  8. Fco.Lopez
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    Fco.Lopez Junior Member

    Better, post recent Delf Series here...

    ;)
     
  9. Jonny88
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    Jonny88 Junior Member

    Sorry to dig this thread up again but could someone tell me please, what exactly has changed with regards to the actual formulas used to calculate residuary resistance?? I understand that earlier models were tested with a keel and rudder and these were factored into the polynomials. When exactly did this change and can anyone tell me where I might find all the different polynomials used and when they were used??

    Thanks.
    J.
     
  10. Paul Kotzebue

    Paul Kotzebue Previous Member


  11. Jonny88
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    Jonny88 Junior Member

    Thanks a lot for that Paul, they're really useful!

    J
     
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