With a little experience in composites, it's fairly easy to fab up foam/fiberglass amas. Gary Dierking covers the topic well in "Building Outrigger Sailing Canoes", which is just a great book for boat builders and outrigger/canoe folks. He's done a number of large amas using foam/fiberglass as well as box-section thinwall ply.
Here's the link to his ama page:
http://homepages.paradise.net.nz/garyd/quikama.htmlThe US Blanks 12'6" SUP blank (EPS, rectangular) could probably provide enough foam for such a project, at 5.5" thick, ripped lengthwise and joined via a homebuilt ply stringer.
http://www.usblanks.com/catalog/downloads/It's EPS so you can use epoxy resin for the glassing, which I prefer over poly.
-RH
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2013 Tandem Island "Victory Lane"
Oahu, Hawaii
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