Tony Arends (Racer X sails) made one for his A cat late last summer. It was a beautiful sail but I don't know if he decided that the extra cost justified any performance increase. It looked like king kong could not pull it apart though. On boats with more powerful rigs... it could offer advantages. I think that on the very stiff carbon N20 mast... you might actually be able to bend it with his string sail.

I am not sure... but the F18 and Tornado classes may ban string sails under their "approved sail cloth rule" which would have crushed development in this area.