Stitch And Glue Kayak?

Well, I gave it a shot once before, last summer, after building a stitch and glue sailboat, with terrible results =( It was VERY unstable and would flop and dump me out the side. I'd like to give it another shot...but before I put $200 into it, I'd like to get some feedback on the design. I believe the problem with the other one was the flat bottom.

The old one was 8'X2'X2' The new design is 8'X2'X1' I want to keep it short so that its easy to transport, and I will be living in an apartment in a few months when I head off to college.

I am building 2 identical kayaks, and I would like to be able to link the 2 together to use as a catamaran sailboat, I think a taller boat would work better for such an aplication, with flatter sides, maybe 2' tall instead? I think the older design would lend itself better to a catamaran than this new one would.

You guys are the experts, can anyone lend me a hand?