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Old 25-07-2016, 06:54   #1
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Why? Jibs on America’s Cup Catamarans

Why? Jibs on America’s Cup Catamarans.

If those mighty wing sails are so efficient, why are they putting a jib out front?

…particularly when sailing upwind, close hauled (which they do very often when creating those conditions with their big foiling speeds) ??

Why would they put that ‘soft sail’ out front? (not the code sail, but the jib)

(nice video clip of wingsail rig,....)
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Old 25-07-2016, 09:04   #2
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Re: Why? Jibs on America’s Cup Catamarans

As I understand it the mini's there as much for maneuverability as it is for power. They could have easily enlarged the wing just a tad to get the same power, but lost the handeling benefits. Since these boats were built for match racing the control, particularly at the starts is critical.

Also keep in mind the code is only used in relatively light wind, the jib actually acts as the down wind sail in heavy breeze (over 16kn I think).
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Old 25-07-2016, 09:09   #3
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Re: Why? Jibs on America’s Cup Catamarans

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Originally Posted by beiland View Post
Why? Jibs on America’s Cup Catamarans.

If those mighty wing sails are so efficient, why are they putting a jib out front?

…particularly when sailing upwind, close hauled (which they do very often when creating those conditions with their big foiling speeds) ??

Why would they put that ‘soft sail’ out front? (not the code sail, but the jib)

(nice video clip of wingsail rig,....)
Without the jib, I suspect the AC boats would have more weather helm than desirable.
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Old 25-07-2016, 09:30   #4
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Re: Why? Jibs on America’s Cup Catamarans

I guess you have never tried to tack a catamaran that didn't have a jib hoisted.
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Old 25-07-2016, 09:44   #5
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Re: Why? Jibs on America’s Cup Catamarans

Stability - when the AC72s were foiling they were preparing to jibe they were foiling on three surfaces, and the jib at the front was on a bowsprit that all teams were tinkering with to get the balance right. Eventually they ditched the code 0 and focused on the jib.

If I recall correctly, during one of the race days the Kiwis almost capsized against Oracle because the wing wasn't properly deployed - and the jib actually saved them.
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Old 25-07-2016, 10:49   #6
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Re: Why? Jibs on America’s Cup Catamarans

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Without the jib, I suspect the AC boats would have more weather helm than desirable.
Healm is easy you just shift the mast or blade location.
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Old 25-07-2016, 13:26   #7
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Re: Why? Jibs on America’s Cup Catamarans

Ok i'll have a go.
Is this a game?



Look at the jib as the third element of the wing sail.

Three elements are more efficient than two, but the theory is all caught up in the law of diminishing returns, complexity reliability and weight.
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Old 25-07-2016, 15:30   #8
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Re: Why? Jibs on America’s Cup Catamarans

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Look at the jib as the third element of the wing sail.

Three elements are more efficient than two, but the theory is all caught up in the law of diminishing returns, complexity reliability and weight.
Completely agree. I think the jib helps keep the airflow attached on the leeward side of the wing at higher angles of attack. Or something like that.
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Old 25-07-2016, 16:46   #9
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Re: Why? Jibs on America’s Cup Catamarans

Wonder how long it will take until these wings sprout slats, maybe slots and vortex generators?
Would the rules allow such?


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Old 25-07-2016, 17:03   #10
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Re: Why? Jibs on America’s Cup Catamarans

[QUOTE=a64pilot;2174738]Wonder how long it will take until these wings sprout slats, maybe slots and vortex generators?
Would the rules allow such?



Then I suppose a winglet would be next?
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Old 25-07-2016, 17:14   #11
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Re: Why? Jibs on America’s Cup Catamarans

You know, I bet the engineers asked that question and did some modeling. The answer is that you see headsails on the boats. The jib must make that wing come alive.
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Old 25-07-2016, 17:42   #12
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Re: Why? Jibs on America’s Cup Catamarans

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Completely agree. I think the jib helps keep the airflow attached on the leeward side of the wing at higher angles of attack. Or something like that.
I suspect your right on here.

This also probably negates the need for vortex generators and other such devices since the jib directs the airflow to the leeward side of the wing keeping the airflow attached to the surface.
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Old 25-07-2016, 18:36   #13
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Re: Why? Jibs on America’s Cup Catamarans

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I suspect your right on here.

This also probably negates the need for vortex generators and other such devices since the jib directs the airflow to the leeward side of the wing keeping the airflow attached to the surface.
Not sure. To keep the flow attached, there would be a major % overlap, meanwhile the jibs are blades.

Blow some air between two closely spaced foils watch the flow.

No jib would mean no turbulence no turbulence would give laminar flow over a longer portion of the wing.

Not sure why the jibs. Maybe there are some benefits just after they tack, while still sailing very slow? Sort of like thinking maybe they benefit from the jibs while still in displacement mode?

Maybe they will shed them in future editions as the whole thing develops.

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Old 25-07-2016, 18:38   #14
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Re: Why? Jibs on America’s Cup Catamarans

They have a jib for the most important reason. The AC rules require them to have a jib. If given a free hand they certainly could have been designed to be as efficient without a jib.
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Old 25-07-2016, 19:12   #15
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Re: Why? Jibs on America’s Cup Catamarans

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They have a jib for the most important reason. The AC rules require them to have a jib. If given a free hand they certainly could have been designed to be as efficient without a jib.

But the racers (or the group of sponsors) make the rules. If they all want to take the next logical step and make the "boats" into gliders, then it would be so. There might be some institutional forces that would resist the change, but money wins in this sport.


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