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Making CFRP battens

  • 05 May 2012 06:41
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    Reply # 912310 on 911490
    Anonymous member
    Our problem both with Footprints and Tystie was that we didn't really know how big we needed to go. I knew that 2" x 1/8" wall GRP tube was OK for a flattish sail, but these cambered sails seem to develop more power, and need stiffer battens. We pretty soon found out that 50mm x 1.6mm alloy tube wasn't stiff enough. If I'd got a company to make CFRP tubes, I wouldn't have known what diameter and wall thickness to specify. A baked prepreg tube may well have better properties than the tubes I've made, but how much better? There's so little data on big, powerful, cambered sails. Someone has to be first, and struggle with getting things right. 
    65mm x 1.6mm alloy tube has proved to be stiff enough for Footprints, but I still feel concerned about the softness of the tube that's available here. With the benefit of 20/20 hindsight, and knowing now that 65mm tube is the right size, I should have imported some tubes of a better, stronger spec than can be found here.
  • 05 May 2012 06:34
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    Reply # 912307 on 911490
    Anonymous member
    Mea Culpa. I'll start a thread on bamboo battens.
  • 05 May 2012 06:19
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    Reply # 912303 on 911490
    Deleted user
    Wasn't that $NZ 1000 per batten?  :-O
    I think the easiest solution is sleeve a couple alu tubes together (with a wooden dowel) to get your 7m length. (OneSteel here in OZ have 6.5m x 50mm alu tubes)
  • 05 May 2012 06:12
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    Reply # 912300 on 912144
    Anonymous member
    David Tyler wrote:Just to bring this topic back to CFRP, and away from bamboo, I should just add that the cost to make each batten was about $NZ 200. The cost to buy a CFRP tube of the same length, diameter and thickness is about $NZ 1000. The cost of an alloy tube of sufficient strength and stiffness is about $NZ 100.


    I am wondering after your experiences whether the $NZ 1000 pre-fabricated tube now looks rather attractive to you ;-)  As you said elsewhere the need to build your own was not one you readily embraced, but forced on you by circumstance.  Of course you also now have the advantage of battens that you can alter/repair as time progresses, and any flex can be resolved.

    ps apologies for the unintenional thread hijack.  Is it worth moving the bamboo comments to a thread of their own?

    Last modified: 05 May 2012 06:13 | Anonymous member
  • 05 May 2012 00:53
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    Reply # 912144 on 911490
    Anonymous member
    Just to bring this topic back to CFRP, and away from bamboo, I should just add that the cost to make each batten was about $NZ 200. The cost to buy a CFRP tube of the same length, diameter and thickness is about $NZ 1000. The cost of an alloy tube of sufficient strength and stiffness is about $NZ 100.
  • 05 May 2012 00:41
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    Reply # 912136 on 911490
    Anonymous member

    Gary

    The treatment used here in China, and as described in Cutting the Dragons Tail is to soak them in seawater for a long time.  By long I mean 6 months, then store them to dry out.  David Chidell decribes a modified version of this process.... he used a friends swimming pool over the winter months, so I assume that chlorine may have been invovled.  When drying them he strapped them to an RSJ, in the roof of his build shed, to straigthen them.  Seems to have worked rather well.  In China bamboo is used as scaffolding poles on building sites, although only for construction of buildings up to about 10 storey.  Exposed to the elements 24/7 they seem to survive very well.

    Peter
  • 04 May 2012 23:23
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    Reply # 912070 on 912010
    Anonymous member (Administrator)
    Gary Pick wrote: No I haven't Arne, not yet anyway. The only treatment I have done is heat the bamboo to get the oils out of the surface layer, it's the oil that the mold feeds on. Just curious, do you know which species you have growing?


    Species of mildew? Ah, of bamboo  -  no I have no idea. They are not more than finger thick and the distance between the knots is around 15cm. A hungry Panda would finsh them off in 20minutes, i guess

    Arne
  • 04 May 2012 22:15
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    Reply # 912010 on 911670
    Anonymous member
    Arne Kverneland wrote:

                                                                             Stavanger, Friday

    Gary P, have you treated or coated your battens with something?

    I remember when I tried bamboo battens on a JR once and the mildew spread on them just in a few weeks. The wrapped sail bundle can be very moist in my area. Lately I have done a test with varnishing a bamboo stick with two-pot polyurethane varnish and this has held fine for about 3 years. The test I did before that was with one-pot varnish, and it only lasted for one summer. The bamboo stick I am talking about is the one sticking out of the end of Johanna’s yard, carrying little burgee/telltale/ribbon or whatever it is called, so it sits exposed to the elements 24-7. Btw, it is grown in our garden on 59deg North. Stavanger Bamboo, think of that!

    Arne


    No I haven't Arne, not yet anyway. The only treatment I have done is heat the bamboo to get the oils out of the surface layer, it's the oil that the mold feeds on. Just curious, do you know which species you have growing?
  • 04 May 2012 18:32
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    Reply # 911806 on 911490
    Deleted user
    One more too-late-armchair-thought about fabricating tubes, based on something I read about on the internet somewhere.

    Epoxy a door skin veneer into a tube around something. I don't remember if they used foam, PVC pipe, or what....but reported that once the first wood skin was epoxied on, it was very stiff. That might be a better choice than PVC to leave behind if you are going with carbon fiber braid as the next layers.

    One more suggestion: If you want to fair and paint them later--you can also get knitted tubes of fabric to epoxy over the carbon fiber...much easier to make round than troweled on fairing compounds. This is something I actually did (with success), when I was re-finishing Flutterby's carbon fiber masts.
  • 04 May 2012 17:10
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    Reply # 911743 on 911490
    Anonymous member

    Good for cross country skiing poles.  jds
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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