pretty good description, by Cary Palmer:

Tacking a Uni is not hard. It's just a series of well timed motions. You
have to come into it with some degree of speed. Sit on the Windward
stern, Drop a bit of mainsheet just as wind blows across center line,
Steer down to about 45 Degrees below head to wind, and come forward to
the new windward hull ONLY after the boat is through the tack and moving
again. Sheet in slowly to the old position as you come across and sit
down on the front crossbar. After you gain speed then try to point the
boat up, too soon and you'll end up in irons. Trick is waiting out the
tack on that new windward stern until the boat is moving, Come forward
too early and you'll blow it and be in irons. Hardest part is when the
wind is really blowing and timing it right to sit out the tack while a
strong wind fills your sail and flies a hull while you're tacking. I
figure I've done it just right if I Have to do a power sit to push the
hull back down as the boat takes off again.
Happy Tacking
CARY