Perhaps the most value added maneuver in shortboarding is the tack. The tack serves the function of keeping you upwind, while riding a board that can be difficult to keep upwind. When you jibe at the end of a reach, you typically lose between 10 and 20 feet. On the contrary, tacking allows you to actually gain a few feet, or at least remain neutral. Here are some tips:
Shift the sail back dramatically to initiate the tack. Steering with the sail, instead of your feet, will help you keep your weight over the board.
Keep your speed up
In order to maintain sufficient speed through the tack, move your feet forward as soon as you initiate the upwind trajectory. Keep the sail raked back to turn the nose through the eye of the wind.
The biggest problem people encounter is that they wait too long before making the transition from one side of the board to the other. This allows the board to fall off a plane and will cause the nose of the board to bury under the water.
Make your move to the other side of the board early. Do so before the nose of the board moves through the eye of the wind.
Make your move quickly
Once you've made the transition to the other side of the board, over-sheet the sail immediately. This will cause the board to continue on the rotation through the eye of the wind. Keep the mast forward and steer with your front foot to begin planning on the opposite tack.
Learning to tack a shortboard will take some time. At first is may feel awkward and unnatural. But with practice you'll begin to see the dynamics involved.
Once you learn the shortboard tack it will allow you to spend more time practicing rather than constantly working to stay upwind. For help with tacking, ABK Windsurfing Camps has an excellent program. They've helped many windsurfers make the leap into competent shortboard tackers.