Air battens on Junk rig?

Discussion in 'Boat Design' started by Diamond Cutter, Oct 11, 2011.

  1. Diamond Cutter
    Joined: Apr 2011
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    Location: Snowy Mountains, Australia

    Diamond Cutter Junior Member

    Has anyone any experience with, or comments on, the use of inflatable air battens with a junk rig, to replace the usual timber, bamboo, aluminium or whatever, that is generally used.

    I'm wondering if the ability to control the pressure and thus stiffness of an air batten would help with controlling the fullness of the sail, rather than just accepting the wind pressure as the main controlling factor - which works exactly opposite to what is desired, of course.

    So far as I know, none of the mechanical approaches to this problem - hinged battens and so forth - have been particularly successful.

    Any thoughts, anyone? Or preferably, any experience or know of experiments?
     
  2. Barnian
    Joined: Jul 2011
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    Location: New Plymouth, NZ.

    Barnian Junior Member

    Barnian

    I think you are on to something DC. Kites have an inflatableleading edge and ribs and if they are pumped up tight they can become incredibly stiff. No reason to not make sail battens like that, except that the junk rig battens rub on the mast and how long will they do that before springing a leak? This is my first post so I'm just feeling my way here. I'll click the submit button and see what happens.
     
  3. Diamond Cutter
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    Location: Snowy Mountains, Australia

    Diamond Cutter Junior Member

    Pneumatic control of sail shape

    Hi Barnian; that was my first post too, so I suppose we can feel our way through this together!

    I'll be using this rig on a proa, so the sail needs to be controllable right through from curved one way to curved the other way. I've seen pneumatic control arms that use an air tube with expandable ribs along one side, so that when the tube is pressurised, it expands more along the ribbed side, so bends away from the ribs.

    I plan to put pairs of these along each side of the sail, so that increasing pressure in in one of the pairs will curve the sail one way, and pressure in the opposite side batten will curve the sail the opposite way.

    I'll make the tubes from polypropylene, and sleeve the whole mast with polypropylene too, so the rubbing friction will be very low. Also, the battens (being like long sausages each side of the sail) will hold the sail away from the mast, to a large degree, when on the opposite tack (or shunt, in a proa).

    I'm going to use "Sunbrella Plus" heavy awning cloth for the sails, 340gsm. It's very heavy, but the strength loss from extended UV exposure is zero! Another worry dispensed with.
     
  4. Squidly-Diddly
    Joined: Sep 2007
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    Location: SF bay

    Squidly-Diddly Senior Member

    just add Wear Strips on each member where they touch.

    could you give us some drawings?
     
  5. Barnian
    Joined: Jul 2011
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    Location: New Plymouth, NZ.

    Barnian Junior Member

    Wow a proa!

    Hello DC, Wow what a spooky stroke of coincidence, I am building a proa too, well not started yet but will an a few weeks. Am in the process of making the vacuum infusion table at the moment. I will be infusing the mast, rudders, rudder mounting brackets, beams and bulkheads and other flat panels. I have toyed with the idea of a junk rig for years but have decided to go with a balestron type boom and a wing mast. The carbon fiber tow for the masts shear web is on its way from the US as we speak. It sounds like you too have done a fair amount of research on making high tech sails out of cheap materials. The Snowy Mountains are quite a way from the sea so where do you plan to sail?

    Ian
     
  6. Diamond Cutter
    Joined: Apr 2011
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    Location: Snowy Mountains, Australia

    Diamond Cutter Junior Member

    Pneumatic control links

    @ Squiddly-Diddly:
    I suppose you're asking mainly about the pneumatic control of sail batten shape? I have no pictures, sorry, but here are some links to the sort of device I have in mind. I won't need anywhere near the range of control that's shown, but the principle is the same.

    6-minute video here: physicsbuzz.physicscentral.com/2010/12/pneumatic-pachyderm-other-bionic.html (not a live link; cut and paste into browser)

    Couple of other references to the same device here:

    http://www.designnews.com/document.asp?doc_id=229892

    http://www.hydraulicspneumatics.com/200/TechZone/Cylinders/Article/False/86387/TechZone-Cylinders (first article on page)

    @ Barnian:
    Good taste in vessel type, mate, and isn't coincidence intriguing? Mine will have two masts, and is loosely based on Rob Denneys "Harry Proa" (thanks, Rob!). As for where I'm going to sail it, I plan to launch it in the Hume reservoir for "sea" trials (about 70km from where I live), and then transport it down to Lakes Entrance, and live aboard while sailing around the coast. The beauty of the design - amongst many other attributes - is that the hulls and deck split apart, becoming three sections each within the trucking size limit.
     
  7. Barnian
    Joined: Jul 2011
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    Location: New Plymouth, NZ.

    Barnian Junior Member

    Hi DC, Yeah mine also loosely based on Harryproa configuration but with Farrier style folding system so the long skinny LW hull folds in under the bridgedeck. 11m LW hull 7m WW hull x 4.5m beam and folds up to 2.4m beam so it can be trailered without special permit.

    Good idea to go schooner junk on a proa. I've made two RC models and tried several sail configurations but not that one. If you can get some camber in the sails it should work good. IMO

    Cheers Ian

    ___________________________________
    Even if you are on the right track you'll get run over if you just sit there!
     
  8. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    I was thinking you meant just hi-pressure inflated tubes

    instead of the normal junk-rig 'battens', thus the sail wouldn't have any non-foldable parts.

    Then you could stow extra(different purpose) sails and just inflate the battens, and hope they all hold air.
     

  9. Diamond Cutter
    Joined: Apr 2011
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    Location: Snowy Mountains, Australia

    Diamond Cutter Junior Member

    Thanks for the comments

    @ Barnian;

    Thanks mate, I'm hoping it'll work out the way it looks in my head. I confess, the first sight of a schooner junk rig was enough to sell me on the concept, and as I looked into it further, it got better and better! Short masts, and low aspect 22-square-metre sails giving little heeling moment which lets me use low-tech construction. I get a degree of self-steering with the sails. It's not a racer, but a civilised cruiser. Should be good. If I find my way across the Tasman, I'll let you know! Final ocean launch around October 2012, all being well.

    @ Squidly-Diddly;

    I'm using cloth (Nolans Sunbrella Plus - Captain Navy) that isn't affected by UV, mould, rot, salt water, or anything else, so there is no need to fold and cover or stow the sails. Reefing is achieved by simply dropping the sail into the lazyjacks, as on a traditional junk. I also plan to have the masts hinged at the partners and easily lowered towards each other (using water-filled 200-litre drums as counterweights). When down, they each rest in a fork at the opposite partners, and the sail is pulled over the deck as an awning, with 2 metres headroom. The battens should be rigid enough to hold up for this use, and their greater-than-usual bulk won't be in the way.

    Thanks for the comments, guys;

    Cheers, Don
     
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