I think I would scrap the cardboard. You will never get it sealed tight enough to keep the water out. Once wet it will lose its strength the boat will lose its strength and your swimming skills will be tested.

Now - what tools do you have? If you have access to saws I would suggest you scavenge for wood and scarf pieces together to make a frame.
Do some more scavenging to get some kind of skin material. Skin might be used truck tarping (comercial tarps not the ones for your pickup) or billboard cover material. I would try for the truck tarping. As for the foam - Fill as much of the kayak as you can with it instead of float bags. then when you do get a leak your boat won't sink.

As others have said, If you want more than one trip from these boats you better choose some tried and true building materials and methods. I have nothing againse inovation on a shoestring (often do that myself), but safety is paramont to most of us on this board. Many a pennyless greenlander made his own kayak with what he had on hand and a few dozen generations of handed down experience.

Check out www.yostwerks.com for some simple skin on frame construction kaykas. I'll bet you can scavenge the materials in less than a week. A little used plywood, some scarfed mill ends and an old truck tarp and you're on your way. The only purchase would be the glue.

Foster

: Scout leader with no money, lots of Styrofoam and cardboard... any
: ideas on how to build a durable cardboard kayaks for 10 year old
: son and 280 lb man. Could the kayak for my son be a prototype
: for the big boat? I really want to use this kayak for exercise
: on local South Carolina lake.

: I have dozens of large Styrofoam (2" thick) coolers in white
: cardboard boxes. I can laminate cardboard on both sides of the
: cardboard. Would use waterproof TiteBond III to glue them
: together, or do i have to use rubber cement? I don't have a
: workshop so I need to create components and assemble it under a
: shed.

: I have seen the kayak plans for $40 online. I want a little better
: design; something like the S&G Guillemot, or am I
: dreaming??!!!

: I am open to suggestions, comments and advice