Fair enough, thanks Mary.
I was able to see 14+ mph on my GPS without much effort. It may have been possible to go faster but since this was unknown territory for me, I was easing the main pretty often because the lee hull was being pushed so far down into the water. The windward hull never lifted completely off the surface.
I find it very likely that others with more experience would have gotten much more speed than I obtained, and I am hoping that someone will chime in with some numbers. I just want to know at what point I can begin to worry about being launched into space.