Schooner Mainsail Area And Total C.o.e.

Discussion in 'Stability' started by mcm, Jun 25, 2011.

  1. mcm
    Joined: Sep 2006
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    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Larson and Eliasson, in the 'Principles of Yacht Design', state that only 50% of a ketch's mizzen sail area is used to locate total center of effort.

    Then what about a schooner's mainsail area?

    And, if the mainsail is identical to the foresail in area, and is stepped aft of the midship station, is it then considered not a schooner's mainsail, but rather the mizzen of a ketch?

    Why doesn't David Gerr, in the 'Nature of Boats' say to only use 50% of mizzen sail area when locating total center of effort?
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    I was about to answer something yesterday, but found a bit contradicting statements in the Larsson&Eliasson.. So IMO.. Either you make the reduction of the mizzen sail area or have the Ce balanced as a ketch with greater lead compared to sloops, not both of them.
    What comes to schooners it's not in my knowledge..
     
  3. Tad
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    Tad Boat Designer

    Geometric "balancing" is only useful to compare like with like, everybody has different methods and thus results (and their usefulness) vary.....

    Gerr illustrates one method, L&E show another, I use another method. My system is that which was used at the Davidson Laboratory of Stevens Institute of Technology, and it's outlined by Tony Marchaj in Sailing Theory and Practice(1964). This method was used at Bruce King Yacht Design for 30+ years.

    The DL-CE method loads the fore triangle 1.7 times the 100% area (I * J / 2) * 1.7......The mainsail (or foresail in a schooner) is taken at 1 (or 100%), and the mizzen (schooner main) at .5.......The mizzen (whatever the rig) is taken at this reduced area due to interference for spars and sails ahead of it, plus it's own mast. Using this method the DL-CE should fall somewhere between 28 and 38% of waterline length back from the stem.

    Rigbalance.jpg

    All that being said the CE in a schooner becomes far less critical due to more opportunities (over a typical sloop) to change the balance with sail trim.
     

  4. mcm
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    mcm Senior Member

    Thanks Ted and Tad; your info helps.

    Tad, 28%-38% measured from the stem not from station 0 on the waterline?
     
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