The windsurfer in the photo is on a sinker board. It does not have enough volume to float him. If he was to sheet in in sufficiently strong wind, the forward motion of the board would bring it to the surface, and he could have a lot of fun. In this case it looks like the wind does not have enough strength for the sailor to use a sinker. He should have chosen a larger board, with enough volume to keep his calves dry.
(That's Andy Brandt, who knows darn well how much volume and wind he needs to sail. And how much you need too. And how to teach you to need less! ABK Windsurfing Clinics come to Long Island on September 20-22, at Tiana!)