: In the various plans and technique books that I've seen, I notice
: that all the composites are either wood covered in fiberglass,
: or non-cored 'glass & resin layups. Is there a good reason
: not to use a foam core? I'm looking at some of the stitch &
: glue plans, and seeing that it would be very easy to replace the
: plywood with 1/8" or even 1/4" Divinycell foam, then
: laying over a layer of kevlar, and layer of s-glass, then a
: couple of layers of s-glass and some strategic carbon for
: reinforcement. Would this not make a lighter-weight boat
: compared to the S&G? It would also be stiffer than a plain
: 'glass & resin layup. I understand there would be a price
: impact, but other than cost what are problems with this
: technique?

This is a very popular technique, and used by some commercial builders. Biggest downside is the price. Big advantage is the material forms easily with gentle heat, and has a consistent thickness.

The foam core material is many times the cost of home made cedar strips. The multiple layers of reinforcing cloth--glass or more expensive exotics like carbon and kevlar--cost more than (a basic layup of) two layers of glass over wood strips, and of course you'll use more resin as you use more cloth.

Ray Jardine has a nice website showing how he does this.

Check out http://www.rayjardine.com/adventures/Kayak-Construction/index.htm

I'd link to a picture of one of his boats, but he specifically requests that this not be done.

As I understand, Jardine has a background in aeronautics, and his use of foam-cored fiberglass is similar to construction methods used by homebuilders of small planes. his site was the first time I was introduced to the idea of heattreating fiberglas to get greater strength from it. It is a good read.

Glen-L has a nicely illustrated description of the process, and sells plans for a "Foamee" boat design. Check out their website at www.glen-l.com. Then use thier search feature to search for "foam core" That should get you to a bulletin board page with lots of comments on the process. Not all are positive, but hey, that's the internet for ya :)

Glen-L's illustrated process can be found by looking at their "One Off Fiberglass Building" instructions. What you want is their info on the Foamee, but take a look at their fiberglass plank system, too. You can get a handlayed fiberglass hull without making a complete mold. All you need is an armature, much like a set of forms for a strip built boat, with just a handfull of strips loosely spaced on it.

Hope this helps.

PGJ