New Britannia

The Sails of the America’s Cup

https://www.sailingworld.com/story/racing/sails-of-the-americas-cup/

While reading this I wondered if the Cunningham for each mainsail skin may be set independently to achieve a different shape for each side. Every time they tack the pistons at the back of the boom adjust the skins to "pop" the sail. Maybe this was why the Cunningham failed and maybe it means they were suffering more when they locked it off than we thought....

Stretch fabric in sails - this has been around for 40 years that I know. We used to use sails with fabric on the bias in the foot so it was super stretchy and let you flatten the foot off to windward and then deepen the sail offfwind-called a shelf foot.

Originally posted by Sam.Spoons I suspect the stuff the AC boats are using is somewhat more sophisticated

and you'd be right to suspect that.

The concave side of the sail needs to be reduced in area, the downhaul probably acts to reduce this, a simple analogy would be zipping up your jacket! Air flow through the two skins keeps it rigid.

The stretch fabric idea has been around for a long time. GP race yachts use a neoprene gaiter around their gooseneck to provide aero gains and reduce snagging at the same time. You also see it on jib tacks to allow for jib tack adjustment on boats with locked halyards.