Freeship Discussion Regarding Cross Curves Calculation

Discussion in 'Software' started by EAP, Apr 3, 2007.

  1. EAP
    Joined: Aug 2006
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    EAP Junior Member

    The Freeship Crosscurves Calculation Shows As The Righting Lever: Kn*sin(theta). Two Questions: First, What Is 'n'? Second, If The Intent Is To Express The Righting Lever As Seen Passing Through The Keel (since There Is No Kg) Shouldnt The Expression Read Km*sin(theta)???
     
  2. Martijn_vE
    Joined: Apr 2005
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    Martijn_vE Marine software developer

    KM is only valid at small angles of heel. At larger angles of heel the metacenter shifts and at those angles it is denoted KN rather than KM.
     
  3. marshmat
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    marshmat Senior Member

    On a related note, although I realize this thread is a couple months old....
    In converting Delftship/Freeship cross curves from KN*sin (phi) to the actual righting arm GZ, is it correct to interpret the Delftship/Freeship output as follows: Divide the output value KN*sin(phi) by the sine of the heel angle to get KN, then subtract KG*sin(heel angle) to get GZ? Or am I misreading something....
     
  4. Martijn_vE
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    Martijn_vE Marine software developer

    Stability issues

    Marshmat,

    I hope the attached image clarifies things a bit.

    Martijn
     

    Attached Files:

  5. Victor T
    Joined: Feb 2007
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    Victor T Senior Member

    Hi!
    That is right only for small angles (< 5 degrees )
    The cross curves (pantacarenes) build for big angles theta.
    Formula would be this: l(theta)=Y_theta*cos(theta)+(Zc_theta-X_g)*sin(theta).
    Because X_g unknown -> X_g=0 -> l_conditional=Y_theta*cos(theta)+Zc_theta*sin(theta).
     
  6. marshmat
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    marshmat Senior Member

  7. Martijn_vE
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    Martijn_vE Marine software developer

    If you look carefully you can see that I'm talking about KN, not KM which is indeed only valid for smaller angles. N is the virtual metacenter at larger angles of heel.
     
  8. despatches
    Joined: Jun 2010
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    despatches New Member

    blagger/gaff

    hi,

    i'd very much like to hear from you if the project is still alive , , ,

    even if the project has stalled temporarily or otherwise, i'd love to catch up and find out how far you progressed, perhaps sneak a preview at your research,

    i am now looking to commence restoration with an original hull, very little to go on rig wise,, but hull good basis as a pattern.

    if you were looking to make a fibreclass hull , or a light cold molded hull, maybe we should talk.

    all the best edward
     

  9. conceptia
    Joined: Nov 2009
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    conceptia Naval Architect

    Marshmat you are correct. KN-KGsin(theta) will give you the GZ..
     
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