Foam Foils Layup

Hello All,

I'm planning to build some foam/glass foils for a small single hander (similar to a laser). The idea is to shape a foam core using a printed out NACA section and cover this with glass (carbon is prohibited in the class and I don't think its worth it from a cost/performance point of view)

Unfortunately I can find any references as to a suitable layup. I was thinking about layer of 400g/m2 biaxial glass (to counter torsion) followed by a layer of 400g/m2 unidirectional. Maybe another layer near the head and where the board pokes out of the hull. Then perhaps a layer of something much thinner, just to smooth things out a bit.

I have no idea if this is over/underkill? Presumably a person standing on the end of the board after a capsize will exert a much greater force than pure sailing forces.

The type/density of the foam is another question (not wanting to open up a giant can of worms!) I was thinking about Airex (60kg/m2 ?). Apparently high density foam can not be hot-wired very easily. I dont want to use low density foam for impact reasons. A wood core is an option, but I really want to try foam simply because I haven't used it before.

Then theres the resin.....I've read tha vinylester is a good compromise between the low strength of polyester and high cost of epoxy.

Any pointers and advice would be greatly appreciated! I'm not to fussed about super lightness, but Im pretty keen to avoid a snapped daggerboard after a capsize!

Many Thanks

 

There are a bunch of threads on this to be found by searching the archives. If you are really interested in avoiding breakage, why not use a laminated Douglas Fir or Cedar core? Light weight is only good if it doesn't break.

If you are building a foiling Moth that's a different story, but for a planing hull single hand hull 1 or 2 pounds more underwater may not be worth the trouble. For that matter you can get people like Phil's Foils to CNC machine a core (foam or wood) for you at low cost instead of trying to hot wire it yourself. I had Phil's machine a composite wood/carbon blank I supplied and it was far cheaper in the long run than doing it myself. What is your time worth?

A major lesson I've learned in 30+ years of professional product development is that although I may have the skills to do jobs, sometimes it is better to farm out work to experts as the real cost is lower.

 

The layup you are proposing may work well.What might cause it to fail is buckling at the base of the slot when you are standing on the top face of the board after a capsize.
Airex make excellent foam,do they recommend hot wire cutting?I have only encountered hot wire cutting in connection with polystyrene,with which it works beautifully,or Rohacell.The company cutting Rohacell used a very hot wire and did the job in a fume cabinet.You could probably find somebody on this side of the Atlantic to CNC shape a core at a price.
The cost of resin is not too significant,assume a 1:1 resin to fibre ratio and i doubt that you will need more than 1Kg including wastage.Not worth bothering with anything other than epoxy if you want to get maximum benefit from the strength of the fibres.

 

http://www.sailingsource.com/cherub/bldfoil.htm

 

I dont think epoxy is any stronger than Polyester Resin - but it certainly is more expensive. Its only required if you use wood for the core.

Poly or Vynil ester will be quite ok and juts as strong if you use foam cores. Its the glass fibre that will provide the strength and stiffness

 

Hmm, I'm not sure about that at all. The mechanical properties of epoxy in the laminate are definitely superior. Its a lot of work and material to throw away to save a few dollars/quid on material...


And 60kg Airex sounds to me far too light, I think it will fail under crushing loads at the case exit.

 

I tend to use a much heavier foam. (Mind you I dont have that much experience)

On the question of resins one word - epoxy, epoxy and epoxy. The price difference of resins is not that significant. However in my opinion epoxy is incredibly easier to layup. Worth the extra pennies every time.

 

I've been hearing that 'Cabosil' to be be a useful candidate for this sort of application....Does it merit any points in this case...?