Sailed there in the 80's and 90's. Boyne/Tannum is a great place to windsurf, there was quite a crew back in those days. Smallish cross-on wave sailing conditions at Tannum in summer. Can also be good for wave jumping at the banks of the river mouth, and smooth water speed sailing inside the river mouth. Also some nearby islands to sail to. If you want bigger waves, try Agnes Waters, and Wreck Rocks to the south.
An old pic of sailing Tannum in the late 80s: