hatchback car topper sail boat - ideas?

I'm after some thoughts. I want to make a small, light weight sail boat that I can transport on the top of a 2 door hatchback (hyundai excel). It only needs to be able to fit one person. I'm thinking the only option may be a kayak or canoe with a small sail but would actually like something wider and more stable and possibly with a larger sail. As I would need the boat to be light weight I'd consider designs that use a varnished fabric skin. The boat is just for pottering around so I'm not worried about speed or efficiency.



I'm open to ideas. The main thing is the boat has to be able to go on top of the car as I don't want to register a trailer.