Coros watches are the only approved speed windsurfing watches on https://www.gps-speedsurfing.com/defaul ... item=coros .
If you're not worried about speed records then the Garmin Fenix 7 is great. I have the 7x, I can record about two weeks of sessions without charging. It automatically tells me how many runs I did in my session and my speed per run, plus all the other stats.