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My apprentice has recently made a fin for his by making balsa ply by gluing 2x 1.5mm pieces of balsa together then shaping the ply and vacuum bagging two layers of uni carbon to each side. the resulting fin was thinner and as stiff (although did twist a bit) as mine. (smart arse).
though vac bagging is out of reach to most hence i put my non vaccing method above which worked fine.
welcome to input and suggestion if anyone has any.
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I used this method without the vacuum bagging but with the addition of 1 lay of 5.7 oz. carbon on the bias on either side. Nice and stiff very little twist. Complete with paint and threaded rods for mounting-4 oz.
I work with a guy that in his spare time makes kite surfing boards. He “vac bags” them using believe it or not a green garbage bag and a normal house hold vacuum cleaner. His boards are used by some of the best kite surfers in this country.
NOTE: the current womans champion comes from Australia and she has one of his boards.
Peter
i have heard of vac bagging using garbo bags and the like using only a simple household vacuum cleaner and it must work for the mate of yours but you could suggest this to him (and is also here for general knowledge)
find an old fridge or freezer on the side of the road or at a tip etc… rip the compressor out of it and short the two wires going to the thermostat. after cutting the 2 pipes coming from the compressor and starting it up you’ll notice one sucks and the other blows. the one that sucks (as long as you didn’t get a compressor that is clapped out) will provide you with around 28 inches of vacuum (25 is optimum for reinforced plastics) but the chances of getting a perfect seal on you bag is very slim so you’ll probably settle into 20 or above inches (but getting a guage never hurts to be sure. i wouldn’t suggest using garbo bags and the like although they may work because the right films and perforated films are reletavely cheap and if used carefully reusable. the major benifit of this system is it’s simplicity and lack of noise (don’t know too may people that’d be happy about their vacuum cleaner going all night until the resin sets) You can leave the fridge compressor going all night and is as quite as a mouse although some may get hot, but lets face it even if it does blow up it probably didn’t cost a cent.
the apprentice’s fin was built with this system at home without giving his family the s#$@s all night long. the next fin i build will be of the same method. I did always wonder about this “fantastic” way of making keels with cnc moulds or the like because you’d never know if your resin ratio is correct - ie if you put too much cloth in the mould it will be resin starved and too flexable or weak, if you don’t put enough it will be too resin rich and brittle. Vacuum bagging using correct methods like peel ply, perforated film, breather cloth and nylon vacuum film will garentee the resin to cloth ratio to be at an optimum = light weight at max strength . (all theese methods are applicable to any parts or hulls not only fins.
the apprentice’s fin was built with this system at home without giving his family the s#$@s all night long.
the compressor was noisy untill vac was reached but after the was raliatively quiet
because a fridge compressor is not designed to run for 6 hours continuesly not pumping air to keep it cool mine started to get warm after about the first hour (it was about 30 celcious) so i decided to put a fan blowing air over my compressor((the fan was the noisiest part of the operation)) which kept it cooler( frige compressors are ment to rum warm) mine was all most too hot to touch by hand befor the fan was added i have pics of the operatin but un able to show you guys dew to the fact that i dont know how to add them.