curved battens in a junk rig to create a "wing"

Discussion in 'Boat Design' started by peterchech, Nov 7, 2011.

  1. peterchech
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    peterchech Senior Member

    This is for a shunting pacific proa rig I will be building this winter. I already have the hull, just need to modify it for shunting and build the rig for it. Junk rigs are popular for homebuilders, but require cambered panels to get some shape. They also are top heavy, somewhat complicated and not known for having good windward performance or a high top speed.

    I want to build a high aspect ratio symmetrical junk rig. Is it possible to give a symmetrical airfoil shape to the battens? (not the teardrop shape, rather think wright brothers symmetrical shape). I would laminate the battens into an airfoil shape using 1/8" thick fir strips, then insert them into the batten pockets of the sail.

    Essentially, this would be a "wing" that can be reefed. The concept could only really work on a shunting boat. The disadvantage would be that it is difficult to feather out in a gust I suppose, and twist may be a problem as well. I am a little concerned with getting a clean leading edge too... But shunting would be so much easier than with the traditional lateen type, and windward performance could potentially be stellar.

    Thoughts? Comments?
     
  2. frasco
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    frasco Junior Member

  3. eyschulman
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    eyschulman Senior Member

    Are you familiar with the Berig camber spar rig? It works on high speed multis as a jib but I think something like it could be adopted to main sails with the potential to increse mast bend proportional to wind with a unstayed carbon spar. I used it with a full batten jib for several years . great with winds 8k and above. Below 8K not enough force to shape sail well. google it see what you think.
     
  4. MastMonkey
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    MastMonkey Junior Member

    I wouldn't discount the typical junk sail so readily. Didn't you already build a Wa'Apa? Gary tried a junk rig and stated he saw no difference in performance between it and the other rigs he has tried. Junk rigs have also been successful on proas. Here is an example that won the New Zealand proa contest.

    http://www.youtube.com/watch?v=h_ILYfWTEbk
     
  5. peterchech
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    peterchech Senior Member

    I plan on putting this rig on my Wa'apa, modified somewhat for shunting.

    Right now I have a balanced lug sloop tacking rig. The problem with the lug is that it is a powerful sail, creating lots of heeling moment but not so much speed. I got it up to about 9.3 knots with crew, flying the ama, but no faster than that and I was constantly feathering to keep from capsizing.

    I fear that a junk rig will have a similar speed limitation, since it is very similar to a balanced lug and essentially is a square rig... a higher aspect cambered lug may be faster. But if I'm wrong, then let me know!
     
  6. Easy Rider
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    Easy Rider Senior Member

    By sewing the sail for camber and installing flexible plastic like battens in pockets in the sail like hang gliders do I think this is possible. Go to a place where they fly hang gliders and look at their sails. See how the battens are held in w small bungies. Some of the battens are or could be modified to work both ways as required for a boat sail. You may learn other things too and even have a good time watching.
     
  7. peterchech
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    peterchech Senior Member

    Interesting...

    I was thinking something similar to maltese falcon, with permanently cambered "yards". Except mine would not be attached to a rotating mast, but instead hanging down like a junk rig.
     
  8. MastMonkey
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    MastMonkey Junior Member

    The junk rig association had the opportunity to compare two of the same model boats one with the manufacturers standard marconi rig and one with a junk rig. The bermudan rigged boat did seem to point higher, but as both boats came off the wind the junk rig had greater speed. Performance varies considerably depending on the type of sail and the point of sail. There are trade offs to consider. If you are already using a lug rig, then I think you are right that you will not see an improvement in performance with the junk. It would be easier to handle though. At some point you will reach a limitation in speed. The junk rigged Wa'Apa Gary built achieved 8.5 knots in light winds and only 100 square feet of sail. Again he didn't see a difference in performance. Most of the boats in his blog seem to average 9-10 knots so you are right in the expected performance. It doesn't take much to make these boats move, but if you are overpowering looking for that last little bit of speed you will have the performance problems you describe.

    I like you idea though. I am sure among the many experiments based on the junk rig you could find something comparable, including the shunting junk rig shown in the link I posted earlier. The "Swing Wing" design uses cambered battens.
     
  9. brian eiland
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    brian eiland Senior Member

    How are you progressing on your experiment?

    Did you happen to see the videos of the shutting proas over on the Maltese Falcon subject thread?

    ...also the other subject threads on 'square rig variations', and 'square rig pointing'.

    I've been away from this 'alternative dynarig' subject for awhile, but a recent inquiry from a gentleman has me looking at the subject again. I had hoped to attract a client interested in going forward with such research, but the world's yacht economy is not that promising at the moment.
     
  10. peterAustralia
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    peterAustralia Senior Member

    Hi Peter

    There are some sketches that I did in the files section of the yahoo proa_file group, Exact same idea. I am at work now, however give me some time and I can drag it out for you. Idea was that the space between the 2 battens allows a ring to go in there. The ring can then pivot around a circular mast.

    Yes how to feather the sail is going to be difficult.

    Additionally, how do you get good luff tension, whilst retaining smooth flow over the rest of the sail. Reefing is difficult too.

    Harry Proas are not for me, I will admit though that the balestron rig he uses does appear to work well. The same rig could be placed on the lee hull.

    There was that Hawaiian proa with two junk sails, schooner rig. Though that had problems with weather healm.
     

  11. brian eiland
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    brian eiland Senior Member

    Dynarig proas....videos
     
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