(Annotated photos and more articles on AC72 Design.)
Thanks to Seahorse Magazine for this excerpt from “Clear the Bench” in the April 2012 issue. Get the CupExperience discount for your subscription or renewal.
Let’s talk about … “the boards, or foils, as designers like you and me like to call them. The traditional foils are straight like the ones used in most boats around the world. Lately there has been a big craze for ‘C’-foils. It really started in the singlehanded A-Class cats. Called a C-foil because it is shaped like an elongated C, with a constant curve from top to bottom. C-foils make the water think the boat is lighter than it is by helping lift the leeward hull a little. Bad news is they are not as good at stopping leeway, their true purpose in the first place.
AC72 design includes ideas from Alinghi 5
Alinghi 5 testing S-shaped foils on Lake Geneva
There are lots of other options for boards, the massive Alinghi cat even tried S-foils. With foils it is truly open season. Good news is we don’t have to make a decision now. We can plug in some boards later.
AC72 design – foils – daggerboards – rudders
Here is what they plugged in”on “New Zealand”
Rudders – not too fussed on rudder shapes, I’ve seen all kind of shapes and they all seem to go the same to me. What do you think? After looking at the Volvo boats with twin rudders slanted out 20° I was thinking we should do that, for sure. Find the angle when the windward hull is out of the water at the optimum height and make the leeward rudder vertical for that angle of heel.
I can see your mind ticking over… you’re right! We should do that same thing with the whole hull. Rather than make the hulls vertical we will flare the bottoms out by, say, 6° so that the leeward hull is vertical when we are flying the windward one. Now we are getting somewhere!
I would have thought it was best to set the rudders up so they were perfectly parallel fore and aft. Seems to me the least amount of drag. But this is contrary to current thinking. The experts say it is less drag with them toed in a degree or two. The thinking is you should never be sailing with both in the water at the same time, so no need to be parallel. As the boat makes leeway the least drag when the windward rudder does touch the water is pointed to leeward by about the leeway angle. Maybe one degree is not enough? Make it two.”
Any questions? Any comments? Add them below!