: I find it hard to believe you're actually encouraging this, but
: regardless...

I did some quick figuring and a single one of these chests will displace about 120 pounds. The bottom alone is over 4 1/2 sq. ft. and 2" thick, or about 2/3 cu.ft., or a displacement of over 40 pounds. A 70 pound kid couldn't get 2 of these underwater !

I recall reading about a raft made from barrel halves lashed together. Gluing 5 of these foam boxes in a row gives great surface area for the glue to bond to, keeps most of that bond above water, and is an easy start. Carve that into the shape of a boat-- just like a surfboard is carved from a foam slab.

Cardboard is used mostly above the waterline for the dragon head and tail. The bottom few inches might get saturated, but that won't affect safety, just the lifespan of these decorative elements.

: Have you actually tried this stuff? I have and it was worthless.
: The bond was very weak. I've also heard that it doesn't hold up
: in wet environments, but I haven't tested that myself.
: IME, that's not possible with the water-based junk.

No, I haven't tried a water-based contact cement on a boat project. That was why I suggested he try it. I was hoping that putting two coats of cement on each piece would give good bond strength, and fill in some of the surface roughness.

If the water-based contact cement doesn't work then he'll have to find a solvent-based contact cement that doesn't dissolve styrene plastics before the solvent evaporates.

There are a few versions of foldable plywood and canvas boats built mostly by boy scout troops. These use contact cement to hold canvas strips to sheets of plywood. The canvas serves as keel, sides , and deck center. Half of it. Is underwater while the boat is in use. Covering it with paint seems to make the canvas waterproof, as on a SOF, and probably improves the bonds effectiveness in wet areas. Several years ago Boy's Life did an article on a troop that did a trip in boats they built like this. Two or three versions of plans on the internet. At least one version is free.

The boat for papa has to hold more weight. There will be more foam pieces used, and that means more foam joints. If the contact cement can't do the job then he'll need mechanical fasteners--probably bolts and plywood 'washers'.

: Be careful. Are you forgetting that he didn't want to spend any
: money on this?

He said he was broke and then he said he had bamboo! Heck, with three pieces of bamboo he can make gunwales and a keel. Hack some smaller pieces into shape for ribs, or curve them into frames, and all he would need to do is skin it with a blue poly tarp. But he wants to use his foam, so we make frames and ribs from foam, and skin it with foam. I'm thinking something
like a SOT with foam sides and a non-structural cardboard deck.

PGJ