I believe the main development on the AC 72's that makes them really go fast is not as much the foils as the wing sails. I believe the main engine on those boats to be the wing sails (2 part articulating wing main, and wing jib) making the boat go incredibly fast (2x windspeed upwind, and 3x windspeed downwind). Plus a really large bag of money of course.
The foils in my opinion act like a turbo charger giving the boat an additional 10-15% boost above what would be achieved from the already very efficient cat hulls by reducing the wetted area.
My opinion of wing sails is they have an advantage because the heeling moment (the force trying to tip you over) is greatly reduced with wing sails vs conventional sails. All the math and physics are different and I foresee a new era in sailing just around the corner. (just my opinion of course)
Here is a pic of my wing setup on my Tandem Island.
This is a pic of the wing jib by itself. ( the wing main is designed but not built yet), this was a pic I took during testing of the wing jib a while back.
The main will be raised by the halyard and reefable (but not furlable), if conditions get bad I will just lower the main wing while out on the water and sail using the jib alone (which has been tested in 30mph+ winds, and is very safe).
The main will be soft semi-rigid (kind of like a parafoil using the air intakes in the front leading edge to make it hard and rigid). The main frame will be just a square box frame (mostly carbon) which will be stepped before launch. The 2 piece wing for the main when reefed will be piled up at the bottom, then hauled up with the halyard (similar to a standard sail on an H16). Once up and pulled tight air coming in the leading edges puffs the wing foils rigid (like a parafoil). The mainsail automatically follows the wind, and is articulated in the center to get the correct camber (look at AC72 videos to see how the wings work). Control is very simple, you just tug on two lines to bend and articulate the joint between the sails. both the main and jib automatically follow the apparent wind, from whatever direction the apparent wind is coming from. Even with my current setup (with a conventional main (not a wing), and a wing jib). I am sailing downwind faster than the wind so the sails are pointing back as if you were sailing upwind (a very strange sensation and opposite to normal thinking). The apparent wind generated from the forward motion is what propels the boat. This is why my spinnakers no longer work, and I can no longer use them (totally different concepts and thinking).
Once the new main sail is completed I plan to dust off my old foils that I built a couple years ago and put them back on the TI. I will hopefully be able to foil upwind then. My current foil setup only works downwind with my huge spinnaker out in winds over 15 mph and is so limited to exact conditions the foils are not worth the effort.
Of course if I had started with a wildcat or a Falcon F18 it would have been a different story, but I'm on a very limited budget, I would never be able to afford a wildcat. If my new wing main costs me over $500 bucks (my planned budget) it will not be in the cards. The now completed wing jib cost me about $150 bucks in materials, and of course I had to design and build it all myself in my garage.
Don't be fooled by some of the videos showing boats on foils racing downwind with huge spins out, that's pretty easy to do and I can even do that with my very limited TI on my foils.
I think what separates the men from the boys is being able to foil upwind. The Trifoiler is a great example. The trifoiler was designed in the early 90's (pre-dates wing sail technology) and is still an amazing and awe inspiring boat (easily 15 yrs ahead of it's time). I simply can't even fathom how fast it would be if it were upgraded to the latest wingsail technology, you would simply fly in all conditions, upwind, downwind it just wouldn't matter. The current design is fairly limited to very specific conditions, I suspect mostly because of the sail designs, all the rest (ie... the hull design, the foil designs, etc) would likely be the best platform to start with, as in everything is already figured out and proven out, and really works well.
I'm still amazed that there are very few boats out there using all this stuff, I would think that everyone would be all over this stuff.
Just my 2 cents, and of course my own opinions