More information? Please don't blame me for my next heretic opinions about sailing (upwind) :-) In a land sailing, glider has potential energy (height), while

More information? Please don't blame me for my next heretic opinions about sailing (upwind) :-) In a land sailing, glider has potential energy (height), while the boat doesn't have any potential energy. This pot. energy makes glider moving forward (and down). Consider glider on a airfield, and a strong wind to the nose - glider doesn't fly up and forward, it can only lift up and turn back. But at the same time, when you have docked sailboat, and a close hauled wind (approx. 30 degrees from nose), the boat will move forward (lift) and sideways (drag). As faster it is, there will be a less drag. Keel doesn't have to be heavy flat area or 300kg torpedo 2 m below hull, it can be just shallow longitudinal slot of meter - two. Again, if there will be no water (neglect weight of the sailboat), just air, the sailboat will not have any tendency to move forward, otherwise this will be fantastic.