I just found this the other day and thought it might be of interest:
http://personal.inet.fi/private/muu/refe.htm
(click on T Speer writings - rest of this web site is interesting also).
I also just noticed something very interesting about a picture Ive had for years. The picture is
There is a vortex shed off both the top and bottoms of the sail (unless the bottom has the gap perfectly closed) and you can nicely see the vortex in this picture. In this picture, the winds were probably 30 to 40 mph and the boat was accelerating but probaby doing over 50 mph (reach is only about 800 foot). The boat went over a patch of snow and some of the snow got sucked up into the vortex. If the boat was doing over 50 mph, the speed of the wind in the vortex must have been awful fast...
wh.