I looked at using EMT for frames, along with billboard vinyl skins as an inexpensive project for a local Boy Scout troop. 3/4" PVC pipe has the right ID to act as couplings for the 1/2" EMT's OD. I figured 6" or 1' sections of the PVC would act as better moment couplers than normal EMT couplings. I did a computer model using a a rough estimate of the PVC pipe's Young's Modulus based on some quick internet searches. The calculated deflections for the PVC/EMT combination was similar to the aluminum tubing in Tom's original design. No guesses on if the PVC coupling would fail in rough conditions though.
The research project looked encouraging, and I bought EMT and PVC for the keel and stringers. I had a cool idea about building the skins without a frame by calculating the required cut sizes in the side panels to create the right 3D hull shape.
Unfortunately that's about as far as I got
. When we received the billboard vinyl it had too many tiny pinprick holes to be airtight for self-made sponsons. We made a number of attempts to get the sponsons patched enough to hold air, but there were just too many holes. Purchasing FOLBOT sponsons will push the project right out of the troop's meager budget. I still think the billboard vinyl would be watertight enough for the skin, but I've given up on it serving as sponson material. I still have the uncut EMT and PVC sitting in my garage wating to pick up the project again.
I keep getting the itch to try again, with heat-sealable nylon sponsons, but for now the project is sitting in the queue behind DIY camping gear and other projects. Wood longbows and hammocks were my most recent distractions; pack cover/ponchos and rain tarps are my current distraction. A play kayak from a campaign sign will follow those (see the Corogami.net website for the concept). If there is a blowout sale on heat-sealable nylon this project would jump back to the front of the queue
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