http://www.peterlynnhimself.com/newslet ... Nl_12.html
I think its a bit premature to be writing off windsurfers.
Sure there will be a cavitation problem if the pressure on the windward side of the fin drops too low. So you avoid the cavitation problem by changing the fin or board. There have been finless windsurf boards many years ago which had tucked down sharp rails.
Last week at Luderitz, they were suggesting that the wind was only about 35 knots when they recorded a 51.69 knots 500m. I'm a bit dubious that they could make that much of a difference by getting their gear tuned just right, because they set the top speed of 52.05 knots in winds of supposedly 40 to 45 knots only days before.
However, they do have a more efficient power source than the current kites, and a better speed to wind ratio, so they still have options.
Sailrocket though, gives them the same problem - they are going to need a revolution to compete with it, but at some stage craft like Sailrocket will get totally out of reach of something where a human is the ballast.