rules do not allow use of the windward foil, I do remember reading something about exceptions (rule 47.3)
Here is the skinny on rule 47.3:
47.3 Preventing windward daggerboard increasing righting moment After starting, an AC72 yacht shall have the windward board draft stripe(s) visible so to confirm that the board is no more than 0.500 m below MWP, unless one of the following applies: (a) the windward board does not penetrate the surface of the water for more than 15 continuous seconds; (b) the yacht is within 300m of a mark; (c) the yacht is within 30 seconds prior to and after tacking or gybing; (d) the yacht is sailing less than 15 knots; (e) the yacht is sailing at less than 90% of its performance relative to the other yacht(s); (f) the yacht is taking a penalty.