Paul, his son and I took a drive to Escalon to pick up some free Aluminum irrigation pipe that he had heard about. While we were there we also picked up 4 free 55 gallon kerosene metal barrels. Our first plan was to use plastic barrels, but these were free and they float just fine until we can source some donated plastic barrels.
The next hurdle was to figure out how to weld aluminum pipe together with my Lincoln 3200HD mig machine. I heard about a kit that would convert the machine for aluminum, so I figured I'd give it a try for $60. It turns out that this kit works just fine and although my 3200 is a bit underpowered for thick aluminum, it has plenty of power to weld .05" wall tubing.
This was my first go around at migging aluminum, so it was a bit sketchy at first. This is only my second weld but I figure that by the time I'm done welding all of this tubing together, I should about have it figured out. For now, the practice welds will go "down" so they aren't as visible. Migging aluminum is tricky business due to the fluctuations in base metal heat and the weird puddle characteristics compared with ferrous metal. I'm thinking that cleaning all of the rusty and oxidized metal off with a flapper wheel will probably make the welds much better.
The first 20' pontoon holder is taking shape. Another pipe will be welded in place on the top with triangle supports welded in at 45 degree angles to give the 3 pipe structure some rigidity. This design should distribute the weight as evenly as possible over the barrel radius and also keep the barrels captive within the structure.
I'm thinking that 3 barrels per side should be adequate for this craft. It will also minimize the span that the pipe has to make and help balance the load across this carefully engineered structure. I'd like to say that I drew the whole thing up in SolidWorks and then did a full FE structure analysis but in reality, I just hacked up some pipe and started welding. I guess a lot of this is just experience and knowing what metals, shapes, and designs will work. How fun it is to think of how this thing might hold up in some choppy waters!!
Another cool thing about this design is that we should be riding at least a 1.5 feet off the water surface. This will come in handy for keeping the coolers, sleeping bags, and other items in their dryest possible state while we navigate uncharted waters.