Biplane rig, differential thrust for self steering?

Discussion in 'Boat Design' started by dustman, Dec 26, 2022.

  1. dustman
    Joined: Jun 2019
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    Location: Tucson, AZ

    dustman Senior Member

    Can you self steer a biplane rigged catamaran by trimming one or the other sail to balance the boat and hold a course relative to the wind?
     
  2. HJS
    Joined: Nov 2008
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    Location: 59 45 51 N 019 02 15 E

    HJS Member

    It is easier and more efficient to trim the centerboards slightly differently to achieve perfect balance. I refer to personal experience from my own catamaran.

    upload_2022-12-27_12-8-1.jpeg
     
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  3. dustman
    Joined: Jun 2019
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    Location: Tucson, AZ

    dustman Senior Member

    Thanks for the input. I am pretty set on using deep vee hulls for leeway prevention(like a wharram) rather than keels, or boards, so will have nothing to adjust in that regard.

    Since I have your attention, would you be willing to share your experience with the biplane rig? Is blanketing really much of an issue?
     
  4. HJS
    Joined: Nov 2008
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    Location: 59 45 51 N 019 02 15 E

    HJS Member

    If the sails are trimmed and sheeted correctly, there is never any "blanketing". Everything can be calculated according to the biplane theory.
    Deep vee hulls are the absolute worst option in every respect. Sorry.
    Don't guess, calculate!
    JS
     
  5. dustman
    Joined: Jun 2019
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    Location: Tucson, AZ

    dustman Senior Member

    Can you point me to good educational material on this subject? Hopefully not too math heavy.

    I would argue that deep vee has a few advantages: less things to break, less things to manage, and has a lower draft relative to keels or boards down. All things I see as being quite valuable. I aim to be able to sail in very shallow water. From my simplistic calculations the deep vee may wind up with 15-20% more wetted surface than an optimal hull shape with optimal underwater lift devices. Though I'm not sure how much it would affect the windward ability, but if it's only a few degrees I think I can live with that.
     

  6. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    It will be more than a few degrees. You'll be able to get up wind, but it would be more like a close reach than a tack. I read a book written by someone who built and owned two Warham type catamarans. The two deep"V" hulls work like two very long, shallow keels and give similar windward performance. Plus you get the extra whetted area penalty.

    But these boats sail downwind exceptionally fast.
     
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