Composite battens and epoxy choice

  • 26 Jul 2015 03:34
    Reply # 3449354 on 3449247
    Deleted user
    Jim Creighton wrote:

    This tread is about composite battens and epoxy. I have introduced wood where it doesn't belong. On the other hand, maybe there is a way to combine wood and unidirectional carbon fibres, incorporated in a multi-layered structure. Or, two halves of multi-layered wood/Resorcinol partly hollowed with a router before assembly, with solid sections at intervals, like nodes on bamboo. Am I getting out in left field?

    What I am trying to get here, is a lighter than usual wooden batten that will not fail because we are using Resorcinol rather than epoxy.


    On my previous flat sail I built the battens from cedar which normally would not be suitable as batten material as that timber is well down in density compared with recommended timbers for battens. I chose cedar because it is very light weight and it was the only timber I could get in the necessary long lengths, (6 meters), without having to scarf the battens. To overcome the bendiness of the timber I put a layer of unidirectional fiberglass (not carbon), on each side of the battens, set in epoxy. These battens were very successful on that sail and gave me comparatively light weight timber battens with the necessary strength and stiffness. I doubt that hollow timber battens would be successful, just as hollow timber yards have not been very successful. If one was to try and go down that route it would be more worthwhile to build hollow carbon tube battens from unidirectional carbon sleeves, such as I currently have on 'Footprints'. They probably would be no more effort to build, probably would not cost much more, and would be a lot lighter and stronger.

    For most sails though good alloy tube battens are probably still hard to beat in terms of availability of the material, cost, and ease of construction. Where a lot of people go wrong with alloy tube battens is by using smaller diameter, heavier wall thickness thinking that this is going to make a strong stiff batten, whereas it is better to go to a much larger diameter tube with thinner wall. Even T5 alloy tube battens can be successful going this way. Had I known then what I know now I would not have made that set of battens from cedar, but would have used larger diameter alloy tube with timber extensions to make up the extra length I needed, it would have been a lot less work.

    Last modified: 26 Jul 2015 05:07 | Deleted user
  • 26 Jul 2015 03:20
    Reply # 3449349 on 3449242
    Deleted user
    Jim Creighton wrote:

    Has anyone considered using Resorcinol glue for (wood) battens? It is reputed to be resistant to high temperatures. Using wood of course. I built my first boat with it, a Hedley Nicol designed 25' trimaran. It requires a close fit but in battens that should be easy.

    I don't think there is any good reason to use resorcinol glue these days when epoxy can be had for reasonable prices, (if you buy other than the big brand epoxies), and is so much better as a gap filler and many times stronger. Another option though could be 'Gorilla' glue which many people are finding to be successful in boatbuilding applications although I don't know that it is really much less expensive than epoxy, just a lot easier to use because there is no mixing required.
    Last modified: 26 Jul 2015 04:05 | Deleted user
  • 26 Jul 2015 01:04
    Reply # 3449247 on 3434311

    This tread is about composite battens and epoxy. I have introduced wood where it doesn't belong. On the other hand, maybe there is a way to combine wood and unidirectional carbon fibres, incorporated in a multi-layered structure. Or, two halves of multi-layered wood/Resorcinol partly hollowed with a router before assembly, with solid sections at intervals, like nodes on bamboo. Am I getting out in left field?

    What I am trying to get here, is a lighter than usual wooden batten that will not fail because we are using Resorcinol rather than epoxy.

  • 26 Jul 2015 00:40
    Reply # 3449242 on 3434311

    Has anyone considered using Resorcinol glue for (wood) battens? It is reputed to be resistant to high temperatures. Using wood of course. I built my first boat with it, a Hedley Nicol designed 25' trimaran. It requires a close fit but in battens that should be easy.

  • 24 Jul 2015 23:42
    Reply # 3448538 on 3434311

    We used an oven temperature of 30C for most of the battens, with occasionally 35C, if I remember correctly. However, it seems that though WEST and similar resins are OK in temperate climates, they are not suitable for use in the tropics. I did sail from NZ to Alaska with CFRP battens, but they were rather overbuilt, due to having some dry spots in the first layer, I had to add a  layer later.

    I think Darren is right is saying that a resin with a high softening temperature has to be the safer bet for battens, and they really ought to be painted white, even so.

  • 16 Jul 2015 00:23
    Reply # 3435455 on 3434311
    Deleted user

    Absolutely, although if I have interpreted the West System technical info correctly, its glass transition temperature after room temp curing is 129F (54C) and this improves to only 142F (61C) with postcuring.  As you say, every resin system is different and there are limits to the Tg achievable, even with postcuring.  We actually built an oven to cure David's parts, but I've forgotten the cure temp we used.  The main reason for my warning is that it is easy to overlook the glass transition temp and there are many epoxies, including the ubiquitous West System, which aren't ideal for battens.  With the right epoxy and light coloured sails, a person would be unlikely to experience this problem.

  • 15 Jul 2015 19:22
    Reply # 3434946 on 3434311

    There is a lot to know about compostites. I am sure I don’t know half of what is to know about it.

    But I have built masts up to 17.5 m, and other things in different ways usings many different materials. I looked around and asked the questions I thought needed answering.

    Epoxy isn’t just epoxy. There are uncountable numbers of epoxies for various uses.  But as I understand it there is a basic rule. Postcuring epoxy composite products wil improve strength. Post curing means heating in a controlled way and to a specific temperature for a specific time to get the best out of the epoxy used.

    The highest temperature used in post curing  becomes the glass transition temperature. If it gets hotter the epoxy will become soft and strength is lost. Therefore post curing is very important for high strained composites outdoors. In the sun surface temperatures will easily pass 50 deg celcius. A part that has cured only at room/shed temperature will start loosing its integrety by then.

    It helps painting things in a light color obviously to keep temperature down.

    Rudolf


  • 15 Jul 2015 17:25
    Reply # 3434843 on 3434311
    Deleted user

    I think you know the history of those sails better than I do David so maybe you can clarify.  I think David Tyler had light coloured sailcloth when he broke that first set of carbon battens and so heating may not have played a role in the failure.  I think David had solved the problem of those battens breaking by adding an extra layer of carbon, so maybe that was a case of too light a layup.  You are right that you should be able to get away with a lighter layup if you use a larger diameter batten.  If you can find it, it would be interesting to know the glass transition temperature of the epoxy you used on Footprints battens.  An epoxy with a slightly higher glass transition temperature and lighter coloured sailcloth might be all that is needed to avoid problems.  

    It has been discussed here before that darker sailcloth has the virtue of holding up to UV better.  It also offers us a chance to make more interesting sails and ones that aren't blindingly bright in the sun.  However, if you have composite batttens it would seem prudent to stick to lighter colours.  The grey Mustang that David used got almost as hot in the sun as did black carbon fibre.

  • 15 Jul 2015 06:05
    Reply # 3434377 on 3434311
    Deleted user

    I also have carbon fiber battens on 'Footprints'. These were kindly given to me by David Tyler. They were the first set that David made for his fan shaped camber panel sail here in New Zealand. Unfortunately for David these battens were of too large a diameter for the batten pockets on his sail but were suitable for my sail on which we had made the batten pockets a larger diameter. I have now used these battens for 3 years in a wide range of sailing conditions including tropical conditions. The odd thing is that whereas David experienced numerous breakages with his set of carbon tube battens mine have never bent or broken, despite numerous crash gybes and other opportunites for them to break. Of note though is that my battens are 60mm in diameter so I wonder if the larger diameter has added more strength. The battens have been left unpainted but have always been covered by the off-white coloured sail cloth, and were not made from WEST resin but a locally produced epoxy resin, although from memory there was some WEST resin used at some point in the batten construction, maybe for over coating.   

    Last modified: 15 Jul 2015 06:13 | Deleted user
  • 15 Jul 2015 04:37
    Message # 3434311
    Deleted user

    Those of you who have been following David Tyler's progress across the Pacific know that he has had some issues with his carbon fiber composite battens.  Since I had a bunch of rejects lying around from when David was here building wingsails I ran some experiments.  It looks like the batten failures are due to the West System Epoxy softening in the heat and weakening the batten.  Since David has bent and broken battens it seems likely the effect is cumulative and not caused by just a single overheating incident.  I've included the details of the experiment that led to these conclusions, and my communication with David below.  If you are considering composite or carbon fiber battens (which are brilliantly light) then be careful of your epoxy resin choice and use lighter colors for your sails.  You can see a pic of the results here: 

    http://www.junkrigassociation.org/page-1401723/42712302

    Hi David, I concluded my experiment with the leftover carbon half noses from the abandoned wingsail design.  It does look like the West System epoxy is softening in the sun and leading to failure.  I did four "battens" in total including a control that had nothing done to it.  Each half-nose-batten was placed on the ground such that it formed a bridge and then I placed a 27lb weight in the middle of that bridge.  One half-nose-batten was left in the garage, it retained its shape relative to the control after having the weight on it for a week.  The natural black carbon batten failed on the first day in the sun (ambient temperature 24C) and I recorded the batten temp at 56C at solar noon.  I painted one batten grey to match your Mustang cloth.  It deformed on the first day and failed completely on the second day. Its temperature on failure was 52C (ambient temperature 23C).  I also placed a piece of your grey mustang cloth beside the battens, it reached a temp of 46C at the time the grey batten failed.  

    One alternative epoxy is Aeropoxy from Aircraft Spruce, it has a glass transition temperature of 194F (90C).  This compares to Wests value of 129F or 142F (61C), depending on which of their values is analogous to the Aeropoxy test.  Aeropoxy gives the test standard, West doesn't.  Still, 90C is a fair bit better than 61C. 


    Last modified: 15 Jul 2015 04:53 | Deleted user
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