Sailing boats' Stability, STIX and Old Ratios

Discussion in 'Stability' started by Guillermo, Sep 3, 2006.

  1. Trif
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    Trif Junior Member

    Can somebody estimate the STIX for the 30 ft. cutter designed by George Whisstock?

    I think this boat might be much seaworthy than many modern day sailing boats, and I'm intrigued by its designated B category, not A. Maybe somebody has a clue for this.

    Best regards!
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Seems to be the centerboard version so it's obviously bit "worse" considering STIX values..
     
  3. Trif
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    Trif Junior Member

    I am not interested in centerboard version, but the deep fin keel.
     
  4. TeddyDiver
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    TeddyDiver Gollywobbler

    Sorry but the data on the page you linked was for the centerboard.. click "Design Data" below the plan prizes to see GZ curves for both versions, and to me it seems that the deepkeel version might be in A category. To know for sure ask from the designer..
    BR Teddy
     
  5. Trif
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    Trif Junior Member

    Well, the designer says it's the size involved in the category given. Anyway, the boat seems sound for me.
     
  6. Crag Cay
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    Crag Cay Senior Member

    There is a size and displacement quotient in the STIX calculation, with lengths less than about 32ft and displacements less than 3.5 tons both being deemed 'undesirable' for an CAT A vessel and therefore heavily penalised. There are some boats that do manage CAT A despite being under 30ft LOA, such as the Fisher 25 and Vancouver 28, but they have extremely high displacements.

    The heightened significance of this 'size quotient' in categorising boats under 32 feet, make the use of the RCD a poor indicated of 'seaworthiness' on sailing boats of this size. Therefore you need to look at all it's qualities and make up your own mind.
     
  7. Trif
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    Trif Junior Member

    I have noticed that Hallberg Rassy 31 has pretty similar dimensions and GZ curve, and it is an A category. At more than 4.25 t, 067 design is quite heavy.

    It is said that Multichine 28 (Roberto Barros) could fit A cat, and is much lighter, has more beam and little lest.

    Maybe adding a bulb, about 200 kg, to its keel could improve a bit. I think will definitely improve its stability. Anyway, the ballast is 39 % of its displacement, not something you could find on modern boat.

    Best regards!
     
  8. TeddyDiver
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    TeddyDiver Gollywobbler

    That's more or less where it is.. there's a lot more difference in the D/L ratio..
     
  9. cduck
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    cduck New Member

    Selection 37

    Alfredoc ---

    I've got a lot of info on this boat (IMS certificates, have done both keel and rig changes). Please feel free to contact me for details.
     
  10. Alfredoc
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    Alfredoc Junior Member

    Cduck

    I've send you an e-Mail

    Ciao

    Alfredo
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Friend Konstantin, from Russia, brings my attention to a bug in the FKR formula at the spreadsheet to calculate the STIX I had uploaded to this thread.

    It was written:
    FKR = 0,875+0,0883*Fr (If Fr >=1,5)
    But it should be:
    FKR = 0,875+0,0833*Fr (If Fr >=1,5)

    I attach here the corrected spreadsheet,

    Thanks a lot Konstantin! :)
     

    Attached Files:

  12. Alfredoc
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    Alfredoc Junior Member

    Ciao Gullielmo, when you can you remember my Stix and my Avs?

    Thanks too much

    Alfredo
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    Ciao Alfredoc,
    you are right and I must apologize. I have been losing my time, efforts and patience at other thread of these forums. Let's come back to work where it worths while. I'll do the numbers for you within this next weekend. (Promised! :) )
    Cheers.
     
  14. Alfredoc
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    Alfredoc Junior Member


  15. Guillermo
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    Guillermo Ingeniero Naval

    Alfredoc,
    I have been working your numbers, for a height of mast over DWL of 16,11 m aprox (as per the drawings) and I get an approximate STIX well under 23, so the boat cannot reach more than the C category. For sure I'm wrong....:confused:

    I'll revise everything tomorrow. Now going for dinner with wife and friends :)

    Cheers.
     
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