I finally have been able to test my sewn polytarp sail for the
MiniCups. I cut this one flat just a little smaller than the polytarp
people say. I placed grommetts every 12" with a 3/16" boltrope along
the spars but not at the trailing edge. I then marked where it would
normally be taped but did not tape it. Next, I used my wifes machine
to sew it with carpet thread. This went very well and it even looks
good. The sewn sail seems to perform fairly well. The next sail will
have some means for reefing.

My MiniCup building is covered in more detail at:

http://home.mindspring.com/~ohara5.0/