How about a boat that only weighs a mere 8lbs (3.5 Kg)?
I found recently Geodesic Airolite Boats - http://www.gaboats.com/ . What a revelation! I have ordered two sets of plans. One for the Sweatpea (The 8lb boat!). This I have to see. And one for the Westport Dinghy 8.
I'll keep you posted when I receive them and my progress in building them.