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Brian Weslake

AC62 modeling

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Great work.

 

There are two rigs for the 62 according to IM right? Which have you shown?

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^

 

?? Yes that was mentioned initially, but I saw no mention in both Prot and Rule (the reverse top camber cure-all, I guess)

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^

 

?? Yes that was mentioned initially, but I saw no mention in both Prot and Rule (the reverse top camber cure-all, I guess)

 

Yep I had a quick skim of the rule yesterday looking for the IM 'variable area wing'. Lots of wing stipulations, but area (one or more) I didn't see. Must have missed it/them.

Dropping a plan to include wing area variation must have repercussions though - in workable wind range/location/scheduling for example.

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Is this all IM meant when he talked about variation?? Jibs +50%, -33%?

 

APPENDIX E — JIB PLANFORM DIMENSIONS
J40 Minimum
J40 Maximum
J60 Minimum
J60 Maximum

Planform Dimensions

etc etc...

 

didn't sound like it:

 

“There are provisions in the new class rule to allow different wing sizes and jib sizes,..."

 

...'and the class rule has the ability to vary the wing size, a little. That will be tailored for the venue.'

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So, can someone explain why the boards have to be so deep? Is ride height needed to be five feet off the water?

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^

Pure speculation, but two things:

- the general consensus is that it's faster to fly low, yet remain above the sticky stuff

- one of the indelible images I've got of AC34 is ETNZ flying straight at me while I watched from above: they were plowing a tremendous hole in the water with the leeward foil, a virtual breaking wave beneath the tramp. It didn't look particularly fast.

 

I speculate that putting the foil deeper might reduce turbulence at the surface - and be faster.

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^^

Or, a more prosaic explanation: get enough dagger in the water to minimize leeway on a point - it's bad for VMG.

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So, can someone explain why the boards have to be so deep? Is ride height needed to be five feet off the water?

my guess is that it's for beating to windward.

Then off the wind, high is fast and possibly foiling gybes are easier if you start out high up as well.

They may need to start drawing the spi pole again. They are going to need that in the lighter winds. That's based on the 72s performance in the light stuff.

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^^^ fun link. Thanks.

 

IMO, high and slow generally looks better on paper than it works in reality. Maybe it's "wallying" [sic, tm, ...], but I think errors at the low fast end have a better screwup : cost ratio. High and slow is a bit edgier.

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Tend to agree.

 

The complications in wind variability resulting from leaving the SF Slot behind could make this subject all the more interesting.

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^^^ fun link. Thanks.

 

IMO, high and slow generally looks better on paper than it works in reality. Maybe it's "wallying" [sic, tm, ...], but I think errors at the low fast end have a better screwup : cost ratio. High and slow is a bit edgier.

 

Actually I think it was the other way around for the AC72s, the high mode was safe and reliable and that is where they spent most of their time upwind. The low mode required some ground to be sacrificed to get onto the foils, and then was only beneficial if you had a wind shift in your favor.

 

According to Jimmy it also exhausted the crew due to the high workload required to stay up on foils without riding too high and going sideways, so there was a definite cost to upwind foiling, which meant they only did it occasionally.

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But having on the fly rake adjustable rudders may change the equation wrt effort.

 

The stated goal being not just windward flight - but flying tacks as well.

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^^^ fun link. Thanks.

 

IMO, high and slow generally looks better on paper than it works in reality.

 

Actually I think it was the other way around for the AC72s, the high mode was safe and reliable and that is where they spent most of their time upwind. The low mode required some ground to be sacrificed to get onto the foils, and then was only beneficial if you had a wind shift in your favor.

Good point. Upwind foiling is different from and in addition to the more traditional "fast-VMG-high" modes. Likely it has its own fast->high range. It looked technically hard beyond the VMG issues. And the very high speed delta as well as the big investment in changing modes amplify the risks.

 

Still, just kind of generically and a little off topic: a more typical yacht's VMG from it's polar doesn't illustrate the full cost of getting to high and slow which can be deadly. The same mistake in a footing mode or it's mirror (getting over speed) usually can be corrected more quickly with less loss. In that sense, high is more risky than fast for a given level of skill.

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But having on the fly rake adjustable rudders may change the equation wrt effort.

 

The stated goal being not just windward flight - but flying tacks as well.

 

The allowance of stored energy will make a difference as well presumably. Averaging out the effort somewhat...

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Excellent, Andrew - you got me eagerly waiting for the next instalment :)

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Visual evidence of the bump in polars. Same angle, different speed: Start low - go fast, start high - go slow.

 

Evidence of Wallying? I've often wondered why ET briefly feints up, then falls off...

 

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I can't say I fully understand these fascinating articles in all there detail, but it does provide me with a possible explanation how TOUSA managed on occasion to 'put on the afterburners' and just leave TNZ for dead in the water, particularly during the last few races.

 

Makes you wonder if TNZ ever really and fully understood the tactical consequences of this foiling lark, as opposed to the purely technical aspects...

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Some windsurfers, particularly the various hybrid classes, have been facing similar issues for years because they have two upwind modes; either pointing higher with the centreboard down and mast track forward in "displacement" mode, or planing with the track back and centreboard up in lower-pointing planing mode. There's a big shift between the two and the same issues come into play.

 

There was some word that Slingsby was trying to tell Oracle to go lower and faster for some time before they did it. I wonder if that came from his windsurfing background and his girlfriend who sails the Olympic hybrid windsurfer?

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I can't say I fully understand these fascinating articles in all there detail, but it does provide me with a possible explanation how TOUSA managed on occasion to 'put on the afterburners' and just leave TNZ for dead in the water, particularly during the last few races.

 

Makes you wonder if TNZ ever really and fully understood the tactical consequences of this foiling lark, as opposed to the purely technical aspects...

'their'

 

Oops!

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Visual evidence of the bump in polars. Same angle, different speed: Start low - go fast, start high - go slow.

 

Evidence of Wallying? I've often wondered why ET briefly feints up, then falls off...

 

I'm not sure you can say the angles are the same, but it's an amazing example of "better VMG" even if (especially if) OR are lower.

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Visual evidence of the bump in polars. Same angle, different speed: Start low - go fast, start high - go slow.

 

Evidence of Wallying? I've often wondered why ET briefly feints up, then falls off...

 

 

 

 

 

I'm not sure you can say the angles are the same, but it's an amazing example of "better VMG" even if (especially if) OR are lower.
Agree - it would be hard to understand same angle. But I do suspect that ET is footing a bit.

 

What is also interesting: OR does not attempt to foil in the new tack. Perhaps they sit there to cover - or the previous tack was lifted - or a bit of both.

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Visual evidence of the bump in polars. Same angle, different speed: Start low - go fast, start high - go slow.

 

Evidence of Wallying? I've often wondered why ET briefly feints up, then falls off...

 

 

 

 

I'm not sure you can say the angles are the same, but it's an amazing example of "better VMG" even if (especially if) OR are lower.
Agree - it would be hard to understand same angle. But I do suspect that ET is footing a bit.

 

What is also interesting: OR does not attempt to foil in the new tack. Perhaps they sit there to cover - or the previous tack was lifted - or a bit of both.

Remember when people were saying the multis wouldn't be fun to watch match race because they couldn't tack so well?

 

Koukel

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