Foils & foiling
Foiling - "the" hot topic in AC72 design. See the video.
AC72 design is governed by a class rule which defines the limits within which the design teams work to build the fastest boat. Fastest at what? Sailing in strong or light winds? Upwind or downwind? Rough conditions or flat water? What is more important - straightline speed or maneuverability? Let's look at how each team has set its priorities.
"To foil or not to foil, that is the question."
Many people have been surprised at the importance of the foils. New Zealand's designers found a loophole in the AC72 design rule that allowed them to build bigger daggerboards capable of hydrofoiling. Oracle Team USA and Artemis apparently felt the intention of the rule was to prevent foiling by limiting the size of the daggerboards and not allowing any daggerboard parts to be movable control surfaces. They appealed to the jury but lost - designers are free to follow what the rule says, and need not try to figure out what the rule writers intended. So New Zealand has systems to move the entire daggerboards to allow stable foiling.
But... we won't know until the racing starts whether a foiling boat gets around the race course ahead of a non-foiler.