Timbo, The only gate start I can think of on youtube involves a motorboat and 800 windsurfers, at La Defi Wind in Gruissan, France. At 2:30min into the video is the start, the preamble is day 1 where only the pro`s took part, something about 50knots of wind being too much to let the whole fleet out - sensible, as it`s blowing offshore.
If you watch the start you`ll see the motorboat head on what would be a port close reach at around 30knots, which is the speed the windsurfers should be doing across his stern, although many were early and had to slow it down..
Now just slow the process down by half for cats, and again by half for dinghies..

http://www.youtube.com/watch?v=HGgFuxHExYo&playnext=1&videos=3vDBIUpBWLY