I think it is useful to isolate the different "lifting mechanisms" of different boards/fins etc for discussions like these
Skims - a skim board is not much more than a flat plate. When you look at a skimboard going upwind hard (photo attached), you can see that the rail is basically cutting the water, and redirecting the stream down, which in turn provides an upward force for the rider. If its done at an angle, that can turn into a diagonal force that can allow the rider to go upwind pretty well.
- skimexample.jpg (101.52 KiB) Viewed 71147 times
Quad/thruster surfboards - these boards are obviously much more buoyant, so they require less flow redirection than a skim or twin tip. When sailing upwind, the board will sail at a better angle if the lifting mechanism is generated off of the fins, rather than the rail. A great way to practice this is to head out on your surfboard in fresh breeze, and sail away from the beach while digging your rail in strong. Similar to this picture.
- kiteraceexample.jpg (67.3 KiB) Viewed 71148 times
Tack back and see how much you progressed. On your next tack, instead of focusing on "edging" (i.e, digging the rail into the water), try to focus on "twisting". By twist, I mean sail the board as flat as you can, and pressure the back leg away from you, and pull the front leg towards you. Think of it as trying to turn the nose of the board upwind. Remember to sail as flat as possible and resist the urge to edge the rail more than needed. In my experience, I make significantly more progress upwind this way.
Formulas - I like to think about formula windsurfers because they crush kites upwind. The reason? I think it is because they can full engage their fin without creating excess drag by edging the rail. An example is here.
- formulaexample.jpg (54 KiB) Viewed 71149 times
Moth - For those of you who know about moths, they crush formulas upwind because they can completely eliminate the surface effects of a planning body. They drive entirely off the "fin"....or foils in this case, and are extremely efficient.
so we've got planning surfaces (skims, and surfboards), and lifting surfaces (fins). I think one challenge with putting fins on a skim, or kiting on a surfboard is that you are combining two completely different mechanisms. A skimboard without fins is great in my opinion because it does what it is supposed to do, and in the right conditions, it can be very efficient.
putting a fin on a skimboard to me is like adding a training wheel....at first it might help for stability, but down the road once you are riding that bike down a steep hill, you will wish that additional wheel wasn't there.
kiting on surfboards is the same...surfboards are designed to catch waves, turn well, and provide lift while the board is relatively flat on the waves surface. When we kite on them and dig the rails, we are executing both mechanisms: getting lift by edging the rail and redirecting the flow, and getting some lift and stability from fins that are usually partially ventilated, cavitating, and with stock surfboard fins, nearly always vortex shedding (when you feel the fin vibrate and hummmmmmmm).
if we focus on executing one of the mechanisms perfectly, we will probably go upwind better (i.e - a good skimboarder or a surfboard sailed flat will go upwind better than an average thruster sailed at a large heel angle. I also would add that I think the fin design is CRITICAL for upwind performance. I think the reason that boards are getting so much attention now is because we have realized that surfboards are not quite right for kiting upwind....so designers have been frantically trying to figure out the right parameters. Fin design on the other hand, is not much different from windsurfing. We sail at similar speeds (similar reynolds #), so the airfoil selection process is pretty much the same. BUT, if you go sail with a bad fin, you are shooting yourself in the foot. A good fin won't mean you will go win races, but a bad fin will ensure that you don't!
ok, lunch break over. i will add a picture of a moth in a second
-patrick
Way to go! 
