FreeShip Hydrostatics and Cross Curves

Discussion in 'Stability' started by terrnz, Jun 11, 2017.

  1. terrnz
    Joined: Mar 2014
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    Location: NZ

    terrnz Junior Member

    Any users?
    It could be my concept or my maths.
    The Cross curves function in calculations gives KNsin values

    Does not

    KNsin = GZ

    therefore
    KNsin-KGsin=RM ?

    where KG is centre of gravity?

    I am using this as a design tool evaluating a concept/design brief.
    It does not need to be accurate to the nth degree +/- 5% would be fine.

    Any practical help would be appreciated.
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    GZ.gif
    In any hydrostatic program the user must manually enter the value of the KG because the software, although it could make an estimate, could also be very wrong.
     
  3. terrnz
    Joined: Mar 2014
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    terrnz Junior Member

    So if we are talking 1 degree, ie RM1 KNsin1*m= RM1 is a rough guide

    where m = displacement

    so m=4200kg
    KNsin1=.035

    RM1=147KgM

    then if we use the Nordic approximation RM30=29*RM1
    we can use a figure of 147*29=4263KgM for emphirical rig dimensioning
     

  4. TANSL
    Joined: Sep 2011
    Posts: 6,004
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    Location: Spain

    TANSL Senior Member

    According to this formula, the KN value is 2.005
    Although perhaps "sin1" means sine of one radian. In that case, KN = 0.04159
    In any case how did you calculate the value of KN?
    See attached file, please.
     

    Attached Files:

    Last edited: Jun 11, 2017
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