Thanks for everyone’s thoughts on the “Vinyl Foam Hybrid” thread, lots of great advice. Thought I’d do a quick recap / summation of the discussion for convenience if anyone’s interested.

So in brief what this all really amounts to is the strip construction method, except using Divinylcel, Corecell, or the equivalent as a core material rather than cedar. I found an old post on the Wooden Boat forum where someone talks about doing precisely this with the foam cut into strips (but he doesn’t post the results). Nothing new under the sun.

In terms of benefits, I think it’s possible that a finished boat made this way might be lighter than the wood equivalent. As for cost, if you compare a sheet of 1/4” Core Cell to a sheet of 1/4” Okume, the foam is significantly lighter, and somewhat more expensive but not a lot more, particularly if you include shipping. I think both the foam and plywood are significantly more expensive than WRC lumber, though, but not versus machined strips. A big advantage of the foam is it seems to be easier to work with - I think some products can be cut with a utility knife. If you don’t have the tools or confidence to cut your own plywood parts or machine your own cedar strips, then you’re looking at as much as $700 to buy them pre-made - if you could make them yourself from foam, that’s a significant cost savings.

Further, some of the foams seem to have decent conformance ability, especially if you use a heat gun. So you could potentially use wider strips, which means fewer steps. Also, the foam surface might not require as much sanding and finishing as the cedar - although I suspect it depends on the effect you want, and if you’re going for a nice shiny gelcoat hull you’d still need to do some fairing and sanding.

In terms of strength and rigidity, my impression is that for a given thickness, the wood is going to outperform the foam. I was reading a FAQ about composite cores, though, and it’s very complicated, but if I understand correctly the core is acting like the webbing of an I-beam, where all things being equal a thicker core is going to be significantly more rigid than a thinner one. So that’s where the “hybrid” notion comes in - maybe there’s a way to engineer a “best of both worlds” scenario. Instead of all foam or all wood, combine both - go with a thicker core, maybe it’s 3/8”, but then only use as many cedar strips as needed to provide structural integrity (ideally something like 6 or 8), with the remaining strips made of the foam. The cedar (or I suppose it could be plywood) would essentially be acting as stringers.

Maybe this approach would make sense for the hull portion of the boat. I myself like the look of white hulls with wood decks, so maybe you do the hull with 3/8” cedar and foam finishing it with gelcoat, and then do the deck in traditional 1/4" cedar strip with varnish. But only if the engineering makes sense, of course, and if there would actually be any significant time or weight savings.