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.

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.

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.

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

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.