Aftmast rigs???

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

  1. DennisRB
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    DennisRB Senior Member

    No that's not what they are suggesting at all. That's what Brian and I have been suggesting :)
     
  2. DennisRB
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    DennisRB Senior Member

    I'm not trying to start any war. I like the idea, I was just commenting on the result of that test VS reality.
     
  3. brian eiland
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    brian eiland Senior Member

    Parallel Slot verse Triangular Slot

    Now one of the questions I would like to see answered by a testing program such as was conducted, concerns the the possibilities that might exist with a parallel slot between the leading and trailing sails (the 2 forestays in a parallel arrangement vs terminating to one point)

    I brought this up yet again over on this aerodymanic discussion thread
    Slot considerations with increasing mast height.



    I eventually got one reply to this question I posed above, from a well respected aerodynamist
    Sure would like to see this tested.
     
  4. brian eiland
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    brian eiland Senior Member

    Nice Looking Aftmast Rig

    Hi Dennis & all,
    I'm going to take the liberty of moving this latest rig design contribution from Isvflorin over to this subject thread, as I feel it is now much more a true aftmast rig rather than an A-frame rig concept he started and titled that other subject thread of his with.


    I think some tweaking might be called for, but overall its a viable and nice looking aftmast rig.
     
  5. Skeezix
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    Skeezix Junior Member

    I have been trying to plow through this thread for nearly a month. Finally into the 50s now, so the dock is in sight. But I'll have to go through it again to tie stuff together in my mind, and to go out to some of the links I skipped. Not gonna enjoy the pointless attacks and axegrinding again, but that is the nature of a forum.

    Anyway. Two questions for you Brian ...

    Reasons for your statement above? You think the centering of effort that the mizzen enables is needless on such a short hull? Or that lowering the centers to decrease heel force is needless with the associated short mast(s)? Other reasons? I am considering your concept for a trailerable tri because the mast shortening makes stepping and stowing so much easier, especially singlehanded.

    I have not seen (or I forget) satisfactory discussion of the rotational force the head of your mizzen puts into the mast via that back spar. Less of a concern with a shorter mast on a trailerable, though.

    I will share my more specific ideas with you privately when I feel I have my mind wrapped around a bunch of concepts better.
     
  6. brian eiland
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    brian eiland Senior Member

    First off, thanks for your perseverance in going back thru this subject thread. It really has grown rather lengthy, but I wanted to keep the discussions in one location rather then dividing them out over multiple threads.

    Just a generality concerning ketch rigs as they are almost universally two masted rigs, ....adding complication to small boats.

    There are a number of folks with smaller vessels that have experimented with ever shorter rigs. Just a few,...markstrimaran on page 50, aftmast gaff cutter on page 50.

    My thoughts are that the point of attachment of that aft jumper spar to the mast would be such that it is free to rotate rather than fixed rigidly and thus twisting the mast tube. The backstay going over that jumper spar is under a lot of tension, and constructed of a material that allows almost no stretch. So it wants to assume the shortest distance between its two attached ends,...that is its position as show in the dwg. If it were to 'sway' side to side, it would have to lengthen (stretch).

    If for some reason this solution is not enough, then two stays from the aft end of that spar down to the shroud chainplates should take care of that.
     
  7. markstrimaran
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    markstrimaran Senior Member

    The ice finally melted.

    It's been a long too warm to go ice fishing much winter.
    I have been staying warm, sewing up a couple of smaller self tacking head sails. As the spring sailing season here is 20++ mph winds.
    Have too read up and see if I missed anything important. Only 3234 unread post. Well too busy for all that.
     

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  8. Skeezix
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    Skeezix Junior Member

    Thanks Brian.

    Have you considered implications for climbing up your mast? I don't remember that being discussed.
     
  9. brian eiland
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    brian eiland Senior Member

    Have not really given it a lot of thought,..its not a primary consideration as to the viability of the rig.

    Fold-able mast steps could be added to the mast, and with its forward tilt might even be easier to climb.
     
  10. brian eiland
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    brian eiland Senior Member

    Wanted to add a more visible link to that alternative aftmast rig I posted just above.

    http://www.vizible.co/p/p.html
     
  11. CT249
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    CT249 Senior Member

    Every time I look at that design I wonder how the person in the leeward helm seat will interact with the jibsheet. It looks as though a highly-loaded sheet is going to pass a few inches to windward of the lee seat. What happens when the sheet flogs?

    It would be interesting to see how it will tack under just one or two sails, with the CLE that far aft unless the staysail is up. Some interesting concepts in the design, that's for sure.
     
  12. brian eiland
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    brian eiland Senior Member

    I don't think he has any intentions of seating a helmsman in that leeward seat, and certainly not in any appreciable wind. Agreed I don't are for the location.

    And I don't care for that very low boom on the aft sail. if anything i think a wishbone type might be better suited. I've also raised the question about substituting a MastFoil 'flap' arrangement for the wingmast/aft-sail arrangement.
    http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/sail-aerodynamics-457-53.html#post767724
    I don't imagine there will be any attempt to sail under just the aft sail, and certainly no attempt to tack with it. Otherwise it should be fine with tacking under either headsail, or both.
     
  13. brian eiland
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    brian eiland Senior Member

    Another though on this question as I was looking at the scale model the other day.

    The fwd headstay will be pulling the masthead both forward and to leeward (counterclockwise rotation of the mast tube, seen from overhead), The masthead backstay will be pulling backward with an equal force, and will likely be pulling to leeward just slightly due the the mizzen sail's force on that aft jumper strut. Seen from the overhead it will be producing a clockwise rotation to the mast tube. the 2 rotations will tend to cancel one another.

    Both will be pulling the masthead to leeward, and that will be fought off by the windward shroud,...per normal.
     
  14. markstrimaran
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    markstrimaran Senior Member

    vizible 105 pivoting spirit boom

    This seems like a weak link.
    What benifit is gained with a swinging spirit boom?
     

  15. isvflorin
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    isvflorin Junior Member

    As Brian mentioned, I don't see why someone would want to use the lee helm to steer the boat. There might not be seats at all on the beam, that's a comfort creature that might be missing. There is plenty of room windward on the mainbeam for people to sit on and enjoy the ride. The CLE is not far back at all, it is near the center of the boat, why ? Because of the overlapping headsail. Too much wind ? Plenty of options. Take the headsail and main down and use the staysail only, still perfect helm balance. Want to use the staysail and "main", no problem, the center dagger pivots aft to adjust balance.

    I can also imagine dangerous situations for people in the way of the running rigging and it is the skippers responsibility to station people around and common sense should be present as well. Flogging staysail is certainly less violent here than a flogging main on a sloop rig. Less canvas to flog, less force, and people should mind the running rigging imho, it's a sailboat after all.
    Cheers
     
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