My friend and I built a canoe catamaran last spring. We used two Nice Canoes from bateau.com, which we had built a few years back. A flagpole was used for the mast and a white polytarp for the sail.
I used a 1/2" piece of plywood for a leeboard. Unfortunately, the mounting was not satisfactory and it broke under use. We tried to make some repairs using "local" materials. My advice: use a very large/strong bearing on the leeboard.
It was fun to sail but would not point worth a damn. Possibly with a better leeboard design/placement it would have worked somewhat better.
We were able to carry a ton of camping gear. Attached are some pics of us on the Turtle Flambeau Flowage in northern Wisconsin.
There is a book on canoe sail design that I found very helpful. I can't find the title right now, but will try to post later.
Let me know if I can help out with your project. I am a mechanical engineer as well.