Firstly, I presume you are talking about a shunting proa, so the wing must work on both tacks, i.e. a single element wing would need to be symmetrical.
Greenbird land yacht and Sail Rocket only sail on one tack.  The wing need not be symmetrical.

Tom Speer: "Rigid wing rigs take the wingmast a step farther, and eliminate the sail entirely. A single, symmetrical airfoil does not produce high lift and as a result the acceleration of a yacht so equipped is very poor. So rigid wing rigs typically have two or more symmetrical airfoils hinged so that they form a slotted flap when deflected. This produces more lift than the wingmast/sail combination.

  See what Blakeley measure re symmetrical individual wing on in figs 4 & 5, then compare to sum of the parts in 6 thru 8.