VPP's and wave drag...

Discussion in 'Sailboats' started by dionysis, Jan 31, 2003.

  1. dionysis
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    dionysis Senior Member

    Hi all,

    I am in the process of developing a VPP for design purposes, and apart from the Havelock-Castles equations in Norwood's "High Speed Sailing", I can find little information on calculationg wave resistance for monohull sailing boats.

    I like to be as exact as possible, so that changes to hull design are reflected in the vpp's results.

    Am I forced into having to come to terms with partial differential equations, or is there a simpler way?

    Cheers, and thanks in advance, dionysis.
     
  2. nico
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    nico Senior Member

    Hi,

    For the wave resistance you should have a look at the Delft series. It is a regression of the tank testing of around 50 boats and includes effect of (LWL,Cp,LCB,...) . I think it is what you re looking for. it is available in the Chesapeake Sailing Yacht Symposium proceedings and/or Larsson books and several others. If no one is availble to you , a can email you the set of equations and coeficients.

    Nico
     
  3. dionysis
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    dionysis Senior Member

    Thanks nico,

    I have heard so much about this series, but have not been able to get my hands on it. Yes, your email would be much appreciated.
     
  4. Mike D
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    Mike D Senior Member

    Nico

    Like dionysis I too would appreciate a copy of the Delft series.

    Thanking you in advance

    Michael
     
  5. nico
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    nico Senior Member

    Here it is

    It is an excel spreadsheet
     

    Attached Files:

  6. dionysis
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    dionysis Senior Member

    thanks nico

    much appreciated nico, will sit down and make a study of your spreadsheet. Thanks again:)

    dionysis
     
  7. dionysis
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    dionysis Senior Member

    some questions about the spreadsheet

    Hello nico,

    Excellent spreadsheet, just some questions to clarify it's use:

    On the data page:
    for hull data : what does Tc, WA, T and form factor mean?

    On the calc page:
    1. What does Rv mean?, and in say, the formular Rv=Q4*hff, what does hff stand for?
    2. What does the column Rresidual mean? Induced drag of hull, or wave drag?

    Just two more questions:

    I think the data: a0, a1,...a8 have to do with the 9 hull shapes of the delft series, but what do these represent? Do I need to know what they mean?

    cheers dionysis

    :)
     
  8. nico
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    nico Senior Member

    Hi

    Tc canoe body draught
    WA waterplane area ( not wetted area)
    T total draught

    Rv is the viscous resistance ( frictionnal + pressure)
    hff is hull form factor ( account for pressure resistance)
    Rv = Rf * form factor ( Rf = Rfrictionnal)

    You don't need to know what a0,a1... mean, they are the factor of the polynomial regression to get the residuary resistance (=wave resistance)


    Nico
     
  9. dionysis
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    dionysis Senior Member

    excellent!

    thanks nico, I owe you one

    dionysis
     
  10. MGLARRIBA
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    MGLARRIBA New Member

    Residual Resistance

    Hi Nico

    I have some information on the LARSON and ELIASSON formula to calculate residual resistance that i feel mest be wrong.

    I have seen in an Excel sheet that you have offeres within this forum, that the third term, that says a2*LCB, comes with a minus (-) in my formula comes with a plus (+), can you confirm me the right one.

    Also, can you tell me if the LCB dimension shown in the formula it's the position of the Center of Bouyancy as a percentage of the Lenght or it's an absolute value?, is it measured from the fore perpendicular or from the main frame in either of my previous question.
    :?: :?: :?:
     
  11. nico
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    nico Senior Member

    hello,

    In the paper LCB is a % value and = (Lcb/Lwl)-0.5 with absolute value of Lcb and Lwl. In the paper a lcb aft of midship is by convention negative, so i just changed sign to put it positive (to my own convention: lcb aft is positive). (-*-=+)

    Nico
     
  12. MGLARRIBA
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    MGLARRIBA New Member

    Thank you

    Hi Nico:

    Thank you for your comment

    MGLARRIBA
     
  13. grob
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    grob www.windknife.com

    Does anyone know where I can get info on the Gerritsma drag calculation scheme?
     
  14. nico
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    nico Senior Member


  15. dionysis
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    dionysis Senior Member

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