S-W-ATH maxsurf model problem

Discussion in 'Software' started by zeroname, May 25, 2012.

  1. zeroname
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    zeroname Naval Architect

    Hi,

    i am trying to build a model with rhino + maxsurf, but i dont understand why i am getting Cp and Cb of this model above 1. anyone can please correct me?

    Regards.


    Edit: had to remove attachment
     
    Last edited: May 28, 2012
  2. TANSL
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    TANSL Senior Member

    May attached figure give you a valid answer?
     

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  3. zeroname
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    zeroname Naval Architect

    yes.. so you want to say in the software they did mistake calculation? because in maxsurf i dont need to define breadth size, they take it automatically... or you can tell me in maxsurf what should i change ?
     
  4. TANSL
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    TANSL Senior Member

    The Cb or Cp, as used in normal calculations, are intended for single hull vessels. So we are surprised that a Cb can be greater than 1. But a value greater than 1, for multihulls, is not a bug. Maxsurf, in my opinion, is calculating correctly.
    I do not remember exactly but is possible that Maxsurf lets you choose how it has to measure the beam.
     
  5. zeroname
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    zeroname Naval Architect

    Yes , there is option for selecting is it monohull or multihull. and also symmetric or not ... i was worried because of getting similar Swath reference data having Cb , cp below 1
     
  6. bhnautika
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    bhnautika Senior Member

    Zeroname have a look at the equations for Cp and Cb and the relationship between LWL and area and volume.
     
  7. zeroname
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    zeroname Naval Architect

    In the attachment you can see , the calculation forumla resulting values below 1. but when i set the hull type as :catamaran in maxsurf, it goes above 1 . and i am even not sure the formula they used for Cb , Cp is will be correct.

    Because TANSL's picture formula will result Cb around .712 which is more logical.
     

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  8. bhnautika
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    bhnautika Senior Member

    Zeroname are you trying to calculate for one hull or both. The figures for Beam at wl is across the whole rather than just one and the same for the max cross section. For the Cb wouldn’t the max beam of a hull be better than the WLBeam (of one hull) as at that point its not a very good representation of the width of that hull . I did a quick calculation based on hull width and got a Cb in the 60’s. The Cp looks reasonable given the hull shape.
     
  9. zeroname
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    zeroname Naval Architect

    I set in maxsurf as Both the hull is symmetric. and Vessel type : Catamaran , putting the centre distance of demihull : 11m .
    can you just tell me what things i should change in maxsurf?
    is your result .60's comes using maxsurf or other tools?
     
  10. TANSL
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    TANSL Senior Member

    You can use the beam that you want but, depending on what calculations, you need to use one or another value for Cb, always thinking about for what are you using this value. If, for example, you need a power-speed prediction you should use a Cb>1.
    See attache what is in HydroMax Manual
     

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  11. smartbight
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    smartbight Naval Architect

    Cp and Cb of this model < 1

    Take a look at Delftship output.
     

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  12. zeroname
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    zeroname Naval Architect

    SmartBight, can u check my model with Delftship ? i am not good at that tools. at DWL =6
     
  13. smartbight
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    smartbight Naval Architect

    Delftship does not read your Maxsurf, ***.msd directly. If you can export your .msd to an IGES format, ****.igs or ***.iges and post it; we could give it a try.
     
  14. bhnautika
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    bhnautika Senior Member

    Zeroname if you look at the output supplied by smartbight the Cb is close to what you got even with a different design. This is I believe because both programmes are using the same BWL position. Look at the three examples, all fit the equation in the calculation sheet (V/L*maxb*maxd). The first one is the one being used in your calculations based on the figures. It comes down to, does the trad ional fit the unusual.
     

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  15. smartbight
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    smartbight Naval Architect

    Ran it on GHS. No time to check output.
    Check it yourself !
     

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