I would like to add a Bundy quote from the really informative piece in Sail-World.

"Bundock puts a dampener on this notion. 'We have had the Nacra 17 fully foiling. In fact we did it downwind, on the first weekend we had here for training. We were completely out of the water for about five seconds, with about 30cms of rudder in the water. But this Olympics, the Nacra won’t fully foil, unless you put some lifting rudders on the boat."