We have a lot of windsurfers moving up the skills ladder here and one of the obstacles of learning to shortboard is tacking. On a big/long board, you can spend a considerable amount of time in front of the mast. The shorter and smaller you go, however, you go from "you really shouldn't be up there" to "you can't be up there". As well, the timing is a bit different as you switch sides before you go through the wind not after.
Here's a nice video of a quick tack on a small board (95 l) at both regular speed and slowed down. Note that foot work and how the sail is backwinded (wind from opposite side) when they go to the other side.
Now, to understand what he did
and a ride along explanation
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More
from Jem Hall Tack tips 1-3. Look on youtube for more.
Windsurfing 101