Sizing Ketch Standing Rigging

Discussion in 'Sailboats' started by Zaynab, Sep 26, 2003.

  1. Zaynab
    Joined: Apr 2003
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    Zaynab Junior Member

    I am trying to figure out how to size a ketch rig (mast and standing rigging). Larsson explains how to size a single sticker's (sloop) rig, as does Dave Gerr in "The Nature of Boats" (easier to understand but less precise than Larsson). Neither book explains how to size the rig of a ketch.
    Suggestions; links; book titles appreciated.

    Zaynab
     
  2. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Suggestion 1 - Assume that the mizzen is used alone for really heavy weather. Size the rigging as you would for the mainmast, but allowing for 75% of max RM as the criterion. This "assumes" a headsail is using the other 25%.
    Steve
     
  3. mmd
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    mmd Senior Member

    Skene's Elements of Yacht Design addresses this issue.
     
  4. Zaynab
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    Zaynab Junior Member

    Thanks Mmd and Steve for the quick replies. I'll have to order Skene's ... I had hoped to save a little and get more recent data by buying Larsson's book. But anyway, all those design books look really cool :cool: on my bookshelve.

    Steve: I am interested in the following approximate sail areas: genoa 25%, main 40%, mizzen 35% (high roach main and mizzen; swept spreaders, no permanent backstay).

    Zaynab
     
  5. mmd
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    mmd Senior Member

    Zaynab, normally I would feel bad for a person who was forced to buy a moderately expensive book (aren't all books too expensive? ;) ) to answer a single question or two, but I think that you will find so much useful information in Skene's that you will refer to it many, many times in the coming years.
     
  6. Zaynab
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    Zaynab Junior Member

    Skene's Yacht Design

    I just received Skene's 8th edition and you are absolutely right, although the author has some ideas that seem to be outdated. I do not want to start a lengthy discussion about long vs short keels, etc., but boatbuilding fashion clearly has changed, and Larsson's book is more modern in that respect.
     
  7. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Zaynab, it's worth remembering that when it was written, Skene's was pretty dang up-to-date. The first edition is from 1927.
     

  8. MikeJohns
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    MikeJohns Senior Member

    The problem with the ketch mizzen is all that added drag from the second rig.

    To compensate the mizzen should be around 20% of the total sail area (according to Pierre Gutelle it should never be less that 18%).

    That way the drive to drag gain is acceptable. If the Mizzen starts getting too small you just slow your boat down.

    Mizzen masts should be designed with the mizzen staysail in mind. This is the big winner on a ketch rig.
     
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