Aftmast rigs???

Discussion in 'Sailboats' started by jdardozzi, May 28, 2002.

  1. brian eiland
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    brian eiland Senior Member

    Not sure of what you speak?

    This tri in the photo is most likely not sailing downwind judging from most indicators, particularly the closeness of that headsail sheeting and the small amount of twist in that fat-headed main
     
  2. brian eiland
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    brian eiland Senior Member

    Yes, and I stuck to the conventional method of centers of the areas just as a conventional rig. I don't claim my individual sails to 'different' from ordinary 'proven' sails.
     
  3. Alik
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    Alik Senior Member

    The aerodynamic CE of sail is not at its geometric center.
     
  4. brian eiland
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    brian eiland Senior Member

    I will have similar problems tacking that an ordinary cutter rigged vessel will have....getting that genoa around the 'babystay'.

    Note that both my mizzen and staysail (mainstaysail) are both self-tacking. The genoa is probably best left alone (allowed to backwind against the staysail) until the tack is completed, and then hauled around....somewhat std operating procedure in cruising vessels with a big headsail.
     
  5. brian eiland
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    brian eiland Senior Member

    I think we all realize that...it is usually forward of the geometric center. But MOST designers for YEARS have continued to use this geometric center rule to happy results.
     
  6. Alik
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    Alik Senior Member

    The CE of sails is moving during tacking motion and resulting aerodynamic force will try to push the boat back on original track once genoa is luffed.

    On conventional rig, this force is balanced by mainsail, but in Your rig mainsail is rudimentary.

    Forget about geometric CE - this does not work in Your case.
     
  7. Alik
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    Alik Senior Member

    ... with conventional rigs where they have plenty of statistical data for this empirical method.
     
  8. brian eiland
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    brian eiland Senior Member

    And I agree with you here.
     
  9. brian eiland
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    brian eiland Senior Member

    On a multihull vessel there are times when guys have had to unsheet the tight mainsail to prevent the vessel from going into irons. The mainsail does not help the tacking situation, but rather may hinder it!!.

    Most important in tacking a multhull is to 'turn' the boat into the tack, and not stall it by throwing the rudders over to quickly. Second it pays to have a nice 'pivot point'. For that reason I MUCH PREFER daggerboards or centerboards to long shallow keels.

    Get the bow just thru the wind, and that genoa will immediately backwind and push the vessel thru the tack.
     
  10. brian eiland
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    brian eiland Senior Member

    That is the first thing I say to a person who is inquiring to my rig....and it is likely the reason it has been so hard to attract clients for this rig. And when I tell them it needs some good engineering work on the final staying arrangement(s) most sailors aren't willing to spend for that extra analysis.

    I don't have any doubts as to the performance of this rig. I do have serious concerns about rigging it properly and substantially. And I have not tried to hide this from potential clients. See "Backstay Tensions" in posting #98 above.
     
  11. Alik
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    Alik Senior Member

    This is guesswork form Your side unless supported by sea trials.
     
  12. brian eiland
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    brian eiland Senior Member

    A-Frame Rig on Kolika

    Did you see this website Stefano...lots of photos and a write up on an A-frame masted vessel:
    http://www.sail-works.com/KOLIKA/index.html
     
  13. brian eiland
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    brian eiland Senior Member

    This is NOT guesswork, it comes from multiple years of sailing multihull vessels, both small and big.

    Have you ever tried tacking a Hobie 14 catamaran??....mainsail only design, and no 'board' to pivot about.
     
  14. Alik
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    Alik Senior Member

    Brian, I sailed/raced B-class cat for many years, plus other bigger cats. Besides, I did a Ph.D. on subject of sailing craft manueverability where did computer simulations of tacking motion as part of research, including tank tests and GPS measurements of trajectories.

    The things You're taking about is Your guesswork, because they are not supported by engineering calculations and/or sea trials. So we want to see prototype boat with Your rig built and tested before can contunue this discussion.
     

  15. Fanie
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    Fanie Fanie

    Alik,

    The recent trip the Vaal dam with the little trimarang with it's aft mast sail had similar responses from some hardened sailors there.

    This one guy told me he saw those aft mast sail setups before... on Kenya lake (the philamons in Africa are years ahead of us) and they can only sail downwind.

    So there you go. Aft mast setups come from Kenya, the philamons have been using it for YEARS there and they have trade winds they sail downwind in only.

    The dumb f idiot at the Vaal never saw me sail in and out of his marina the three days we were there. The wind blew us out and back in so our timing must have been good coming in and going out.

    It was rather a matter of him being very PO because he was trying to catch us in his big mono, and he never even came close. Beat him to wind too. He must have been an inexperienced sailor.

    If I was you I'd stick with what you was tought in the phd. This sailing setup will not work for you. It requires a bit different thinking and as I said before there is a few tricks to it you miss.

    Now you know why nobody sails them ;)
     
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