Can you actually get a degree in sail design? I know it's a craft where you can be an apprentice and do a masters test when done as apprentice. But can you go on and do a degree on saildesign?

As for wind shear, it depends on what kind of wind you have, stable or unstable. My literature suggest it can be quite pronounced (25deg) even in the height-range of catamaran masts (I have never experienced it so pronounced). It can also be as small as 2degrees at your masttop. (Ref: David Houghton and Frank Bethewaite). What you are thinking about is probably how friction between wind and earts surface, and earths rotation (coreolis effect) wil influence the wind. Short version is that becouse of friction between the wind and the surface, and becouse the earth rotate wind further up will have a different direction than closer to the surface. As earth rotates in the same direction all the time, you will need less twist to compensate on one tack than the other.
My experience is that twist is beneficial in some conditions, but should be avoided in others. When overpowered (as Gary looks to be in the picture), twist is good to shed power and eliminate form drag. Twist is also beneficial when powering trough waves or accelerating. In flat water, looking for power, I feel faster with less twist. This will increase power (again, depending on wind shear), but also increase form drag from the sail.
Sloop rigs need to twist their mainsail to compensate for the jibs influence on the wind. On our Tornado main we have used 8 degrees of twist, and I think it's a bit too much (might be a problem with cloth stretch and luff curve). I have also heard that 11degrees of twist are designed into Tornado mains. For a uni rig, I would expect less twist designed into the sail. But how it's trimmed on the water is what decides how fast it is (unless it is out of the ballpark).

When trimming windsurfer sails, it's critical in my experience to have the correct mast for the sail. I trim downhaul until the leech just goes slack when looking for power with it. In stronger winds, I put on more downhaul to keep the sail manageable. With the wrong mast, your leech will go slack to early, or overpower you completely
The main 'brakes' you can put on when sailing cats are form drag from the sails. If you go out in 0-1m/s winds, wind shear will probably be pronounced , so you need twist to power up the top and keep the telltales flying. You have probably also heard that in weak winds you need deep sails to make the boat go. So, how do you induce twist while keeping the sails full? You let out on the mainsheet. That way you will have a full sail and decent twist. If you have tried this, you know that you will not go well to windward and be slow. If you crank on the downhaul and sheet in (still fly the leech telltales 50% of the time) to flatten the main, top will twist off while the lower part of the leech still stands. What you really have done, is remove a large part of your sails form drag as the wind dont have to move over that deep curvature (and probably detach from the surface underways) but instead follow the much more efficient shallow curvature. If the wind increases, you can trim your sail deeper with less twist as the increased power generated by the sail is larger then the added form drag.





Sorry for the rambling.. I just find this stuff very interesting.