Alright, I'm going to take a stab at this as I have learned it from numorous people and books I've encountered over the years.
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<br>Draft Position Fore and Aft
<br>Putting the draft forward makes the foil less "critical", meaning that the foil will maintain laminar flow over a wider range of angles of attack. Of course, this is at the cost of additional drag. From what i've been told, pushing the draft forward to about 20-30% makes the foil more forgiving in maintaining flow in choppy conditions. Pushing the draft back to about 50% increases the efficiency and works well if the foil is not disturbed too much.
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<br>Depth
<br>The depth of the foil governs the amount of lift that the sail provides. Of course this is also at the cost of drag. The deeper the sail, the more drag. Also, deep foils will not maintain laminar flow at higher air velocities.
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<br>Using this information, you can see that there really is no direct correlation between the two. It depends on apparent wind speed and how stabil the foil needs to be (flat vs. choppy water, your ability to sail to a consistent apparent wind). For example, if you are sailng in flat water and a good breeze, you will want the draft at about 40-50% and the depth to be abit shallow.
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<br>Of course this also depends on your ability as a sailor. the really good guys are able to have a lower drag, more critical foil and maintain flow when the lesser guys need to have a more forgiving shape. Those are my thoughts, and hopefully one of the good guys will chime in and provide alittle more insight. Good Sailing.<br><br>