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Sam.Spoons View Drop Down
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Posts: 3400 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Topic: New Britannia
    Posted: 28 Jan 21 at 8:53pm
It looked like it had a proper zip rather than velcro. The bottom of the sail needs to brush the deck to maintain the end plate effect so I reckon that's where the stretchy stuff is most beneficial.
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423zero View Drop Down
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Posts: 3420 		Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 21 at 8:47pm
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.
Robert
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Mozzy View Drop Down
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Posts: 209 		Post Options Post Options   Quote Mozzy Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 21 at 8:18pm
I reckon it's just a neoprene cover for the downhaul, attached to mast with velcro...
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iGRF View Drop Down
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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 21 at 7:12pm
Originally posted by Sam.Spoons

I suspect the stuff the AC boats are using is somewhat more sophisticated  LOL
and you'd be right to suspect that.
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Sam.Spoons View Drop Down
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Posts: 3400 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 21 at 6:43pm
Early Demon Design race sails used a stretchy luff panel made from a single sided laminate with what looked like a knitted scrim. I suspect the stuff the AC boats are using is somewhat more sophisticated  LOL
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Oatsandbeans View Drop Down
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Posts: 382 		Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 21 at 6:28pm
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.
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iGRF View Drop Down
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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 21 at 12:42pm
The sail has a stretchfabric at the clew which is fixed, so they adjust shape without reducing area, hope that hasn't given anything away that can't be seen onsite, but if that fabric gets released it could revolutionise the way we make sails.
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GybeFunny View Drop Down
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Posts: 403 		Post Options Post Options   Quote GybeFunny Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan 21 at 7:10am
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....
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ClubRacer View Drop Down
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Posts: 210 		Post Options Post Options   Quote ClubRacer Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 21 at 8:58pm
https://youtu.be/N8--jRxcXgM?t=9804

Using the graphics at the bottom, from the moment both boats are on their respective tack (port for ineos and starboard for prada) you can see Ineos lead dissolve rapidly. If you've ever got your self into that position you'l know the options are a massive luff to get behind them/ gybe to windward of them or keep going and hope you're clear.
If you've done the massive luff in a spinnaker boat (which I would say these things are closest too when they're screaming downwind) you'l know what the chances of success are. They had plenty of time to prep for a gybe if they needed it and had plenty of time to execute it even after Prada beared away. They took their chance on the cross and judged it just right. 

The rules upwind prevent you (ROW) bearing off towards another boat (GW) from the moment when GW is pointing behind your transom (dial down) but nothing stops you as ROW pointing at their transom first and then slowly heading up (dial up) as long as you while you're changing course you're giving them room to keep clear (basically the only option as GW without infringing is to tack) There was a good video of I think Nick Thompson doing it at an event a couple years back, I think Oman or possibly Princess sofia 
16.2 In addition, on a beat to windward when a port-tack boat is keeping clear by sailing to pass to leeward of a starboard-tack boat, the starboard-tack boat shall not bear away if as a result the port-tack boat must change course immediately to continue keeping clear. 

For the AC these are inverted for downwind. A ROW boat cannot luff to towards a GW boat that is already taking the ROW boats transom. But nothing stops you doing it the other way around (As Prada did) as long as it complies with 16.1 
16.1 When a right-of-way boat changes course, she shall give the other boat room to keep clear.
AC Rule only: 16.3 When sailing to a mark that is to leeward, a starboard-tack yacht shall not luff to a course that is above her proper course if at that moment the port-tack yacht that is keeping clear by sailing a course to pass to windward of her has to immediately change course to
continue keeping clear.


Edited by ClubRacer - 24 Jan 21 at 9:12pm
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Rupert View Drop Down
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Posts: 8956 		Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 21 at 8:03pm
So, you are passing clear ahead on the angles being sailed. The ROW boat can bear away provided the give way boat has time to keep clear. But where can the give way boat keep clear to? If they luff, they slow down, makes things worse. If they bear away they get closer, makes things worse. They are committed to passing, as would be clear ahead without the bear away, so can't tack without getting in the way. So surely the ROW bear away would have to be early enough for give way to have time to tack, duck or slow.
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