foam plastics

[keith]

I am looking for a stuctural foam that is flexible to build athwartships in hull sections. Epoxy with fibre later This is for space savings While building. All the foams I have read about appear to be rigid and lend themselves to length wise construction only. Any ideas?

[Jeff]

I'm sorry Keith - I missed this thread until now.

You've probably already found what you were looking for, but if not, when you say you need a structural foam that is "flexible", you mean more than the typical scored foams. What thickness do you need? I don't quite understand the project at hand as you say 'this is for space savings while building".

For others viewing this thread, we have also added a new article to the Design Articles section of Boat Design Net:
Foam Core Materials in the Marine Industry by Trevor Gundberg, Composite Materials Engineer with DIAB Inc.

[keith]

Jeff,
What I am endevouring to do is find a means of boat construction
building the hull/s in cross sections of say stations of for instance 6 feet and assembling the finished sections else where. What I am saying is for small areas one could build say7 six foot sections of a 40ft craft, the sections would be stored until the boat is ready for the cross sections to be joined by stringers of some design. If this type of construction was possible I envisaged using a flexible type foam similar in behavior to say a open cell flexible polyurethane and finishing with epoxy and glass/carbon.

I can,t seem to find a structual foam of this flexibility.
Thanks for the reply mate.

Regards Keith Emms

[Jeff]

I think I'm finally correctly visualizing what you're thinking of, though I'm not sure if this has been done.

Initially I thought you were intending to use the foam for the stations/bulkheads, so the requirement for flexibility I did not understand.

Now I think I correctly realize that you want to use the foam for the skins, but only in 6' fore-to-aft sections which will then be bolted/screwed together or otherwise assembled later.

My question would be why do you want to skin your boat in these small sections? If you are going to fiberglass the whole, why not also skin the whole? My primary concern would be fairness. I would be worried that you will end up with hard spots and irregularities where the sections are joined, as the foam won’t lay as evenly since it is cut into 6’ sections. The nice thing about the traditional batten – foam – fiberglass approach is that you use the long battens to provide smooth curves as they lay over the stations/bulkheads. You also can see any errors early on. It would seem this approach will mean a good number of extra stations being needed, doubling up every 6 feet.

I’m not sure I can answer your question, but I believe Airex is the softest and most flexible of the mainstream structural foams, followed by ATC Core Cell, whereas DIAB Divinycell and Klegecel are more rigid. I know that if you are serious about your project you can get samples from the manufacturers so at least you can feel what the foams are like hands-on.

I would still like to know though what the advantages are of constructing and skinning 6’ sections rather than just cutting the stations and then assembling them where you will do the final skinning/fiberglassing work? Is it a construction site limitation, or are you having someone else do the fiberglass work and you want to do as much as possible in one location first? Or are the sections integral to the finished project?