A couple initial thoughts after reading ricks post.

1. The sail would probably not be optimized for down wind. It would probably be too flat especially for a boat like the hobie 18, which does not generate that much apparent wind.
2. The furled sail will cause a lot of wind resistance.
3. It will be useful in a small wind range upwind, downwind is were you have a lot more potential increase in speed.
4. How will it affect pointing when it is flying?
5. Richard Howard of rudder chaos fame (video on thebeachcats.com) built a similar sail for his hobie 18 (see video). Hopefully he will see this. If not message me and I will send you his email.
6. I contacted Calvert to build my spin and their prices were way higher than any other sail maker I talked to.

I have never used a hooter, which pretty much makes this post useless.

Matt