And why are “elements” and “slots” important?
Since we got the first photos of Artemis’s AC72 wing there have been many questions about the wing’s configuration – how many elements? How many slots? (For the basics, see this short video explaining wing stucture and controls here.)
Wing AR 2 slots? jjga
Artemis wingsail: 3 elements. How many slots? Copyright ? Annotations: Jack Griffin 
365 x 260 Artemis Racing
First sail of the Artemis Racing AC72 wing. Valencia, 15 March 2012. Photo copyright Sander van der Borch / Artemis Racing
Let’s compare with the two element wing on USA 17 in race 1 of the 33rd America’s Cup Match against Alinghi 5 in Valencia in February 2010. Look at the dimensions of the leading and trailing elements of Artemis’s wing and USA 17’s. Quite a difference!
USA17 camber-TM jjga
Two element wingsail of USA 17 in race 1, 33rd America’s Cup. Annotations: Jack Griffin
Camber is the angle between the leading and trailing elements. (You knew that, right?) By the way, here’s how camber is controlled on an AC45:
Wing AC45 camber control jjga
AC45 wingsail camber control – Copyright Jack Griffin
It will be interesting to learn about the control systems for Artemis’s wing. Kimball Livingston quoted Artemis CEO Paul Cayard last November as saying the wing would have 38 hydraulic cylinders. True? Or disinformation to throw off the competition?
In the same article, Kimball wrote:
The Artemis approach to efficiency, Cayard says, uses a three-element, two-slot wing. No surprise. Any wing is much more efficient than a mast and soft sail—for many reasons, not the least of which is that mid-leech tension becomes a non-issue—and C Class catamarans long ago demonstrated that three elements, two slots, are faster than two elements, one slot. I expect every AC72 to have a three-element wing.
But that might not be quite right… Here’s a picture of a C Class catamaran’s wing. An aeronautical designer would say it has two elements, one of which has a flap. In aeronautical terminology, the number of elements = number of slots + 1.
595×446-Wing-C-class-detail-3-el-2-slot-jjgb
Wingsail design: C-Class catamaran wing with 2 elements + 1 tab
Do you think the Artemis wing has one or two slots?Comments? Questions? Answers?
What are the advantages of two slots?
How will the control systems work on AC72 wings?