Resistance prediction methods/series for catamarans

Discussion in 'Multihulls' started by Roni, Jul 8, 2020.

  1. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    There are just rows and columns of numbers. So it means nothing..could be a simple typo, who knows???
    Where is the baseline input data and how it is translated into THOSE numbers in your spreadsheet?
     
  2. guzzis3
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    guzzis3 Senior Member

    No. I haven't got all the information it requires, and remember I am blind so finding that stuff is a nightmare. Sorry.
     
  3. Bureau Naval
    Joined: Oct 2021
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    Bureau Naval Junior Member

    Here there is a new version of my former spreadsheet. Sorry for the lack of information, but I belived as it was not protected, anyone can follow the results. Anyway, a shor explanation is, the input data is the dead rise in midship section (16 degrees), the angle of the transom wedge (8) and the L/LBH ratio (11.5). The calculation, for simplicity, was in the followings columns (P, Q, R...) for the volumetrics froude. Down each column is the summa of the values and the Residuary drag-weight ratio, from this vaue, it is assumed that the Resistance can be calculated. Sorry for the delay in the reply, bus I was trying to finish other delayed project..
     

    Attached Files:

  4. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Thanks.
    But, again, it is just series of numbers and reference to where the numbers/data is coming from to provide any meaningful commentary.
    You are being blinded by the numbers and not focusing on the objective.
     
  5. Bureau Naval
    Joined: Oct 2021
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    Location: Argentina

    Bureau Naval Junior Member

    Dear Ad Hoc, thanks for your interest...
    I'm going to try to explain again what I was trying to do.
    First, a simple check of the Muller-Graf method with a minimum of data taken from his own work.
    What do I need to calculate the resistance? Only three figures, the angle of the dead rise in midship, the angle of the transom wedge and the L/B ratio. I took those 3 figures from the work and make a simple spread sheet, and I had a great surprise when I got negative values of the Residuary/Weight ratio coefficient...
    It's as simple as that. Do not try to do an in-depth study, for that is the next stage once the accuracy of the method has been verified. I copied the coefficients from the work, replaced them in the formula, and.... Get negative figures
    Second. I always try to start from the simplest to the most complex and seeing partial results. So, if there is a problem, it is easier to find and solve.
    Third. In this particular case, I can't get pass over the first part. I took the values directly from the work, to save time, I looked in different places to see if there are published works using this method to calculate the resistance, but unfortunately I could not find any. That's why my post in the forum, perhaps, someone who works with this method, using my data could check my results, I din't try to make any speculation. My spreadsheet is open to anyone who wants to see and review it. The only thing I ask in return, if you find an error, to make it notice me
    Fourth and last. My goal is to calculate the resistance of a catamaran with chines, I don't know how precise the application of other methods will be. This seemed to me the optimal one, since it was developed for that type of forms.
    And thanks again for trying to help me (sorry for the extension of reply)
     

  6. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    My point is this:

    upload_2021-12-13_9-8-38.png

    No one can follow how you arrive at those numbers.

    You have just 3 cells for input....so, ask yourself this question.
    How do you - manually - calculate volumetric Froude number...and then where is that procedure in your spread sheet?

    How can you have a Fn(v) = 0 too?
     
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