Is there a plywood frame with foam glued to the plywood, kind of sandwiched?
Not really. Typically the only wood is the box you sit in on top of the foam deck/hull. Most designs are much like a surfboard deck with the tail cut off for the stern. If you want to power the boat it has to have a wooden transom.
Is the foam wrapped in fiberglass cloth?
Yes, or it will snap it two when you step into it once on the water. The foam has no strength of its own. The fiberglass on all sides is where all the strength comes from. The glass skins the foam turning it into a kind of "I" beam.
Is the pink foam better/worse than the bubble white stuff?
The extruded polystyrene (pink stuff) has a little more strength than the expanded beads. It is also easier to shape. The expanded beads just tear out and leaves you with a rough surface to glass over. You want a smooth surface or you will use twice the epoxy really needed. Another issue with the foam is that the dust gets everywhere and is harder to clean up than saw dust. Once loose in the air the particles become static charged and kling to anything and don't want to come off once they are on something. Seriously messy.
Glue I used is poly ureathane from Elmers. Their version of Ape Glue. It was about $2 cheaper per bottle.
Over on the Refuge there are several foam boat build threads that have really good depictions of the process used for each one.
This is the largest thread with the most detail.
http://www.refugeforums.com/refuge/showthread.php?t=435143
This is my "Duck Monitor" foamer built specific to the type of marsh grass we have up here. It won't work well in other areas that have grass that lays down. When grassed it turns into a little grass island amoung all the other little grass islands. Pretty deadly. A buddy borrowed it and tore up the bottom dragging it behind his ATV and I have yet to fix it. Maybe this next spring.
http://www.refugeforums.com/refuge/showthread.php?t=425261
It is important to use epoxy resin and not poly resin for the glass. Poly resin is solvent based and will melt the foam upon contact.
It is important to not have any air spaces between your sheets of foam. I did not consider this during the build and after a year my boat has several delamination bubbles where the differential in air pressure inside the glass to outside caused the glass to pull away from the foam. If I would have used more glass of higher weight it might have been stiff enough to resist the forces, but then it would have been just as heavy as an all wood boat. I would not do another foam boat these days since I can build a boat out of plywood cheaper, lighter, and stronger.
