The original question asked if a boat could be built from foam. The answer was and is "yes".

Glass-foam-glass is same as scrim-foam-scrim.

If you use bead and cove router bit, the edges of foam will not have open gaps needing filling and fairing as your described foam system.

A simple "female" mould is all that is required. We aren't building in the "traditional glass process" as you described, and have no need to support gel, glass, mat and glass core. Simple wooden female station templates serve to define the shape - and to support the foam.

Mechanical fasteners are NOT required - you use a little dab of hot glue to hold the foam strip in place on each female template.

In case you missed the first posting - please read the following article - and discuss the merits or shortcomings with the guy who built the boat - all I was doing is passing on his method in response to the original question. Each person is going to make their own decision if this is a viable alternative method for their needs.

"Quick Hull-building
From: Dave Culp "

I have been asked about a quick easy way to produce one-off foam sandwich hulls I used to build one of my boats. It's just a simple foam strip plank set-up, using CAD-generated mould sections. The trick is that a) the hull half-sections are small enough that the moulds can each be got out of a half-sheet (or less) of plywood (so you're just cutting holes in square pieces of 1/8" doorskin ply), and b) with CAD, it's no big deal to build a mould every 6-8", so you don't need stringers.

It is then put together on a large jig. In my case, 2 x 2's were screwed to my workbench, and to saw-horses set beyond each end. The foam strips (3/8" x 1.5", for a 20' hull), are laid in, and just hot-glued to the moulds. Very little tapering is done; what's necessary is done by edge-bending the foam, on the bench, and cutting with a straightedge and knife. (Very elegant tapers result, and it takes only seconds to do).

Once the foam is in, the inside is glassed (and left very rough--no finish resin yet, and no sanding). The half-hull is braced (half a dozen sticks, again hot-glued across the hull), and popped/cut out of the moulds. The whole mould/jig is disassembled and re-assembled, front-for-back, resulting in a "mirror" image in three dimensions, and the whole thing is repeated to get the other half-hull.

Both halves are carefully trimmed to centreline marks, and the hull glued together (not hot glue this time, but resin). We used scrap foam "tabs," glued alternately on the inside of the hull-halves to assure alignment. When the resin set, the tabs were removed and the inside joint taped with 2" glass tape. The stern got a foam transom later, and the bow a solid block of foam, carved to get the shape.

I now had a "solid" hull, glassed/taped together inside, and raw foam on the outside. I cut a bunch of moulds down to make a cradle, and began fairing the foam until I liked it - Surform and a long sanding block. (I'd eliminate the Surform next time, and just use a long block with 36-grit paper). I filled the gaps in the foam with microballoons (less than two quarts, on a 20' hull, and 3/4 of that ended up on the floor as sawdust), faired again, and glassed it.
Lastly, I finished off the cockpit rim, put in the seat-back/bulkhead, and a hatch for the beer. The hull weighed 40lbs, before we added mounting pads and hardware.

I did all the above, completely alone in a single weekend - about 18 hours total, from gluing the plotted paper stations to doorskin ply with rubber cement (much faster than transferring the lines) to final sanding. The only power tools I used were a table saw to rip the foam strips, and a sabre saw to cut the doorskins. I did all the sanding by hand. Newly cured glass is as soft as pencil eraser, if you get it at just the right time. As I had laid up the boat with small batches of resin, I could follow this cure state around behind myself. This trick I learned from Jim Brown on Searunner tris.

Mind you, I have built a hull or two, but never before with either the CAD stations, nor of foam strips. I have hand-carved hulls from solid foam, so am not afraid of shaping to eye, but I used no tricks beyond mixing the resin pretty hot, and moving fast. I expected a pretty rough finish, and would have allowed broad tolerances (speed boats are throw-aways, after all, and this hull was not meant to touch water at anything over 12-15 kts), but was astonished at the quality it produced.

I give complete credit to this technique to Greg and Dan Ketterman. -- They used it to prototype all the TriFoilers, Avocets, and for LongShot herself."