Yeah true, they reckon the F50's foils cavitate at 48kts but can power through it a few more knots. I'm sure if they designed specific speed foils they could go a bit faster. I'd suggest though an F50 has a way more efficient power source in their solid wing, and way more righting moment due to the platform layout and differential rudder rake. Given a windsurfer can't hope to get near that, can you design an efficient enough foil at those speeds? I believe the one phantom have designed for their 40kt attempt is around 300cm^2 or something like that....which is about 1/3 the area of a normal race foil. Next becomes the issue of actually controlling it? As for it being safer, I'd expect the crashes are going to be extraordinary