My first windsurfing Gopro video on Youtube. Helmet mount which was aimed higher, but slipped down to show board and feet, which was a different/better angle.
The GoPro Hero5 Black has a built in GPS (so does GoPro Hero6 & 7 Black, and some other action cameras). The speed and other readings can then be overlaid in the video processing/editing. That was the reason I chose the GoPro Hero5 Black.
Dashware software allows a lot of information to be overlaid and is pretty easy to use: www.dashware.net/