At the time, the winged keel was seen as a radical move. The interpretation of the deed of gift for the cup is that a) there should be no technology used that is not available to everyone and [in theory at least] the boat should be built of materials available in the land of registry. In the case of the winged keel, the race committee evaluated it and ok'd it, which made it legal. It was a technological leap but so were sail tracks and highfield levers in their day of introduction.