Kites can also go 3x wind speed in the right conditions
Sorry for being skeptical, is there a video or some web site talking about that ?
This is doable on raceboards in light wind with flat water.
I've gone 25 knots (on GPS) using my old 183x59 raceboard, crappy stock fins, and 18m Dyno in 10 knots of wind. I'm sure the top riders on the best equipment can hit 30 knots in 10 knots of wind.
As the wind speed picks up though, the max board speed doesn't really go up much more than the low 30's knots, they just head further downwind at the same boardspeed.