OK, I'm sure this has been asked many times before but it's Christmas eve and I've had a few reds.
Back in the mid 80's there was a windsurfing movie and the opening scenes were wave-sailors cutting up waves but filmed from underwater. I was sure the movie was called Tradewinds but when I google "Tradewinds windsurf movie" I get a movie with an animated caveman guy learning to windsurf and I haven't watched the rest.
This movie had a fair bit of Australian content, including a totally out of sequence bit about Bob McTavish and some sort of attempted flying windsurfer. I think there was also some speed sailing scenes.
Anyone from back in the day will know this movie. I watched it with a few hundred others at the Sydney Opera House!