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A tied hybrid system for junk rigs -- can it work?

  • 24 Jun 2015 12:56
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    Reply # 3402019 on 3399298
    Anonymous member

    Hi, 


    I was wondering if anyone had tried making a sail out of individual curved panels,  lashed as tightly as possible to the batten...leaving no gaps but an easily made cambered sail?

    Would this need a bolt rope stitched on perhaps?



    regards

    Martin
  • 24 Jun 2015 08:32
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    Reply # 3401631 on 3401472
    Anonymous member
    Darren Bos wrote:... I'm just concerned that the gaps between the panels are likely to obscure much that could be learned. 
    That's a definite possibility.

    I need to take another look at Joddy Chapman's PhD thesis and see what testing methods he worked out. If I do get any results it would be good if they were comparable with his. And he may have some good tips for model building and testing. I have some thoughts about measuring forces to get a handle on the drag caused by gaps.

    It would also be fun to figure out how to generate a nice thin stream of smoke and see where the air is going over the sails.  Then we might be able to see the vortices, and especially turbulence around the gaps.

    More things to do while sailing. Even with the autopilot on and a course set I never seem to run out.
  • 24 Jun 2015 03:49
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    Reply # 3401472 on 3399298
    Deleted user

    Wow Richard, your idea has definitely gathered a lot of attention.  I spent a pleasant hour looking through the JRA back issues and couldn't find the article Paul mentioned and my Google Image search for Thai Junks didn't reveal any boats that had individual sail panels lashed to their battens with the attending gaps between the cloth and the batten.  However, Paul's and my comments aren't necessarily contradictory.  I don't doubt there were boats that used this system and it was likely good enough for what they wanted to do and worked for the materials they had on hand.  Hopefully someone can elaborate on these boats.  

    I'm convinced the gaps will cause a significant loss in efficiency to windward (downwind the gaps might actually help), but I'd also be happy to be proven wrong.  You might also consider whether you will be able to extrapolate from this sail to other sails.  The ideal camber for a sail with slots between each panel is likely to be different than one that doesn't have gaps between the cloth and battens.  I agree that one of the major weaknesses in Junk Rig development is the lack of comparison between identical boats with the only difference being the sails (a racing fleet would be ideal) (yes, I realize this is a pipe dream). I think your idea of being able to manipulate the camber on a single rig is a good alternative, I'm just concerned that the gaps between the panels are likely to obscure much that could be learned. 

    Last modified: 24 Jun 2015 06:47 | Deleted user
  • 23 Jun 2015 13:52
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    Reply # 3400492 on 3400481
    Anonymous member
    Gary King wrote:

    I can see the hassle of making a smooth curve tying all that lacing, as Arne says. How about loose foot and loose head panels?  Much like  mains on some Bermudas boats, only need to  adjust the tension then. 


    I did think about that, having trimmed loose footed Bermudan sails quite a bit.  They rely on the cut of the sail and high tension to get a good aerofoil sail shape, with the belly fairly far forward. You can adjust its position with the kicker and the outhaul. I'm not certain that a long rectangle attached at the corners will form a good aerofoil with the belly forward, but I can certainly try things like that out.
  • 23 Jun 2015 13:48
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    Reply # 3400490 on 3400468
    Anonymous member
    Arne Kverneland wrote: PS: Could it be an idea to make one full size test panel first and take it out for a dry-sail on the beach or somewhere first, to see that it looks ok?
    I was thinking about a test panel last night.  I can knock up something with some non-stretchy fabric, string, and broom handles just to see what sort of shapes I can get.  If it looks promising, I can make a single pair of battens and a single panel that I can attach to Tammy Norie, probably by rolling up ("upward reefing") hersail and lashing it below. That would at least give some clues.

    I'm just about to start building a Hebridean wind vane -- more of a priority -- so this might take a while.

    Last modified: 23 Jun 2015 13:53 | Anonymous member
  • 23 Jun 2015 13:20
    Quote
    Reply # 3400481 on 3399298
    Deleted user

    I can see the hassle of making a smooth curve tying all that lacing, as Arne says. How about loose foot and loose head panels?  Much like  mains on some Bermudas boats, only need to  adjust the tension then. 
  • 23 Jun 2015 13:05
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    Reply # 3400468 on 3399298
    Anonymous member (Administrator)

    Richard,

    I agree 100% with David; try it! Even we, who have made a few sails, cannot foresee in detail from our armchair how your suggested sail will work. Technically it is close to Roger Taylor’s sail, but with the additional freedom to adjust the camber in harbour, and then settle on what is enough and what is too much camber for your boat (..much discussed here, over the years...). The lacings will finally describe a similar curve to what the “round” does on my cambered panels.

    Two points:

    1.      Be prepared for a lot of work to tie up all those individual lacings to get a smooth curve. I guess I would use a system with rolling hitches, which can easily be adjusted in small steps. I suggest you tie up the sail indoors, first time and then bring the whole bundle on board.

    2.      The grommets in the four corners of each panel will see much higher loads than the others. I suggest you at least replace these grommets with stout hoops from webbing.

    Good luck!

    Arne

    PS: Could it be an idea to make one full size test panel first and take it out for a dry-sail on the beach or somewhere first, to see that it looks ok?

     

    Last modified: 23 Jun 2015 15:34 | Anonymous member (Administrator)
  • 23 Jun 2015 08:29
    Quote
    Reply # 3400299 on 3400147
    Anonymous member
    David Tyler wrote:

    An experimental rig for messing around with to find out what works and what doesn't? Go for it, Richard! That's what I've been doing for the last 30 years.


    Ah, but I should stand on your shoulders, not your toes!
  • 23 Jun 2015 06:13
    Quote
    Reply # 3400147 on 3399298
    Anonymous member

    An experimental rig for messing around with to find out what works and what doesn't? Go for it, Richard! That's what I've been doing for the last 30 years.
  • 23 Jun 2015 01:40
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    Reply # 3399999 on 3399298
    Anonymous member

    I suppose I ought to point out that one of my big motivations is experimentation.

    I've seen debates on these forums about whether 10% camber is too much, or whether split rigs are any good offshore, and so on. The things is it's very hard to draw any real scientific conclusions, given that it takes a lot of effort to build a rig.

    So I suppose I'm trying to think of a way of building a "test rig" that I can mess around with, where I can sail with different camber or sail plans on the same day in the same conditions with the same boat.

    There more to this than I've explained in my post, too. I have ideas for easily changed sheeting systems, for example. Adjustable mast rake I've mentioned before. I'd like to carry a set of same-length "universal" battens that I can try out with different shaped panels, even if they end up sticking out a bit with some plans.

    What I might end up with is the worst of everything, but it might be interesting nonetheless.
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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