There are two aspects of this move. He explained one in this video. The other one is getting a feeling for the duck. You don't want to throw the sail to far down and you don't want it too far up. I would just train this in light winds whenever you have the chance. Everything happens slower and you can develop a feeling for the duck. In light winds (non-planing winds) you'll have to go really far into the wind before you duck though otherwise it won't work. Then work on moving the sail more forward and less into the wind. If you move the sail too much into the wind then this can of course cause the sail to be too low when you've completed the duck. Another thing you can play around with is carving the board into the wind while ducking (very slightly). Sometimes if you put a little bit of foot pressure onto the upwind side of the board, you'll carve into the wind a bit and even though the sail doesn't come up your hands will be able to reach down further (because you're leaning into the curve).
@@stauffap Hi,thx for advice it,finally I did it year ago.The problem was I put a lot of pressure on my heels so I always carving to the wind to much during ducking.Recognized when the sail is ducking I must hold the course straight or very little upwind