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      Abbreviated rules   07/28/2017

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Nodrog

Too much data ? Having a guess at Polars

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On 27/06/2017 at 8:49 AM, ~Stingray~ said:

IMG_1621.PNG

Oh I hadn't noticed this is a summary of all 9, thought it was just race 9.

Pretty interesting: if OR closed the speed gap in races 5-8 then the gap in 1-4 + 9 averaged out well, thats a pretty serious overall speed & VMG advantage to ETNZ.

 

Quote

Full list:

 

Upwind speeds seems contaminated by dialdowns & mark roundings, can we get something to separate them out? TWA?

Fastest non-dip/rounding upwind speed I recall seeing was ETNZ 34kt passing OR-JPN in leg 3 of their RR Race on 2nd June.

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2 hours ago, hoom said:

Oh I hadn't noticed this is a summary of all 9, thought it was just race 9.

Pretty interesting: if OR closed the speed gap in races 5-8 then the gap in 1-4 + 9 averaged out well, thats a pretty serious overall speed & VMG advantage to ETNZ.

 

 

Upwind speeds seems contaminated by dialdowns & mark roundings, can we get something to separate them out? TWA?

Fastest non-dip/rounding upwind speed I recall seeing was ETNZ 34kt passing OR-JPN in leg 3 of their RR Race on 2nd June.

Here's a snapshot of a crude attempt at that, could get more select-specific if you'd like

Max_Speeds_Upwind_AC35.PNG.906ff307364d2f4e0f800c599f31104b.PNG

 

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So now we know the reason for the zebra line - pretty unbelievable that ETNZ ran with only 2 accumulators while the other teams struggled with 3!

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17 minutes ago, ezyb said:

So now we know the reason for the zebra line - pretty unbelievable that ETNZ ran with only 2 accumulators while the other teams struggled with 3!

Interesting! Link?

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Just now, ~Stingray~ said:

Interesting! Link?

'One of the things that not many people know about this campaign was that we only ran two accumulators (a pressure storage reservoir of hydraulic fluid) on board, and not three. We decided to take the extra weight of an accumulator off the boat because we believed that our guys could top up the accumulators quite quickly, which allowed weight reduction.

'While the other boats started off with more stored energy, we believed that we could get around the track cleanly, with the weight saving, and utilise that energy elsewhere.'

A pretty good read all round:  http://www.sail-world.com/NZ/Americas-Cup---Glenn-Ashby---How-the-Lone-Wolf-won-the-Americas-Cup/155112

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Quote

Here's a snapshot of a crude attempt at that, could get more select-specific if you'd like

I think I need to rewatch those windy OR-JPN vs Art races.

Edit: nope those were 6 June, 8,9 & 11 are different.

11th is ETNZ vs Art finals.

 

Edit2: that top speed one 17060624 is the 2nd race on 6 June.

I see Arts 47.x at top mark starting leg 6

uCbgsnh.png

But I don't see the OR-JPN 47kt on leg 1.

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56 minutes ago, hoom said:

But I don't see the OR-JPN 47kt on leg 1.

Best I see is 46.8 bearing away to the run

yDNozqC.png

 

Art has 34 upwind & a whole heap of 33.x genuinely upwind on leg 3

glO7aU0.png

 

Hmm Art has 47,2 on bear away end of leg 1 of the earlier race

AORh4An.png

But OR-JPN is supposed to top speed there :wacko:

 

Both have a good bit of 33.x upwind coming up to mark 3.

Lots of 39-41.x from both on the downwinds.

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@hoom  Do have best VMG Data from the races?

Thank you for your posts.  The one I posted sums it up for me ETNZ better VMG all round ??

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Hoom ^ 

I could take guesses but do not know for certain what VE uses in those displays.

In this attached .xls, you could find the exact same SOG and COG values in the matching NAV.CSV files on the Race Data site, minus the extra columns that my data includes (unless you go to the work of also adding those extra columns by using the matching Events.csv file)

 RACE_17060624_SWE_JPN_SOG_COG.xlsx

You can see the 47.22 spike in that file, and just SE of the 'SOG_SWE' label here:

RACE_17060624_SWE_SOG.thumb.PNG.8b8cddddc99d6ce22b3df2994b9aa24c.PNG

 

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On 6/14/2017 at 2:36 AM, southseasbill said:

Why would cavitation happen at a lower speed upwind vs downwind?

Cavitation depends on the foil's loading.  When the loading (lift coefficient) increases, the pressures are lower on the suction side, particularly toward the leading edge.  At low lift coefficients, the sections are shaped so the minimum pressure occurs well back on the chord.  As the loading increases, the pressure distribution on the suction side becomes more negative and flattens out.  The section is typically designed for the pressures to be very close to the water vapor pressure along the entire forward half of the chord at the design loading and speed, leading to a flat "rooftop" shape to the pressure distribution.  At higher loadings, a leading edge suction peak forms, and the foil needs to be operated at much lower speeds to avoid cavitation.

Thickness decreases the pressure on both sides of the foil, and the shaft sections need to be thicker than the wing sections because of the higher bending moments reacted by the shaft.  This leads to cavitation starting first on the lower shaft and elbow (due to interference between shaft and wing), then spreading up the shaft and down the elbow as speed increases.

Upwind, the loading on the shaft is greater because of the higher side load from the rig.  This leads to a lower cavitation onset speed compared to downwind.

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On 7/1/2017 at 2:45 AM, hoom said:

Edit2: that top speed one 17060624 is the 2nd race on 6 June.

I see Arts 47.x at top mark starting leg 6

But I don't see the OR-JPN 47kt on leg 1.

Yes

That 47.20 is in the data files and can be seen like this

RACE_17060624_LEG_1_SOG_JPN.thumb.PNG.aa8890d48d5f2775916af7f1fb0a15d7.PNG

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On 6/27/2017 at 8:49 AM, ~Stingray~ said:

IMG_1621.PNG

How can ETNZ be 2.7% faster in a straight line but 3.4% faster in VMG?

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8 minutes ago, ~Stingray~ said:

Both faster, and tighter angles?

My data doesn't match those numbers perfectly for some reason, which makes me a little suspicious (of them ;) ) but the match is close enough that their chart values can be used for arguments-sake.

 

Fair enough.  

 

I'll ask this in case it's already been answered.  I'm pretty skeptical about the numbers and how they are measured.  There was a moment where Ken Reed was talking about the stats, the two boats (OR and ETNZ?) had the same average speed, the same average VMG, they has sailed the same distance, but ETNZ were 400m ahead. So:

 

Do/should they calculate VMG on the average TWD, or per boat?

Do/should they exclude tacks and gybes?

Edited by Ex-yachtie
edited questions to make them answerable...

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5 minutes ago, Ex-yachtie said:

Fair enough.  

 

I'll ask this in case it's already been answered.  I'm pretty skeptical about the numbers and how they are measured.  There was a moment where Ken Reed was talking about the stats, the two boats (OR and ETNZ?) had the same average speed, the same average VMG, they has sailed the same distance, but ETNZ were 400m ahead. So:

 

Do/should they calculate VMG on the average TWD, or per boat?

Do/should they exclude tacks and gybes?

That could happen if they were using the TWD off each boat to calculate the VMG, and one boat (OR in that example) was in wind relatively out of phase (course-wise) compared to ETNZ. Trailing boats often do gamble, while the leading boat has the luxury of taking the shifts or covering.

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Here is the explanation of base data set that their 'stats' are presumably based on...

 

https://docs.google.com/a/acracemgt.com/viewer?a=v&pid=sites&srcid=YWNyYWNlbWd0LmNvbXxub3RpY2Vib2FyZHxneDo3MjEwMWY4NTFhNzlkMGZi

 

https://docs.google.com/a/acracemgt.com/viewer?a=v&pid=sites&srcid=YWNyYWNlbWd0LmNvbXxub3RpY2Vib2FyZHxneDoyYTExNTQ4Yzg3ZGRmNTQ1

 

Some of the fields were not valid for the AC45s (or the marks) but only came into play with the AC72 - and yes that is the up to date version,

 
Melanie Roberts,
Feb 10, 2017, 7:24 PM

ACDUH!

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4 hours ago, Basiliscus said:

Cavitation depends on the foil's loading.  When the loading (lift coefficient) increases, the pressures are lower on the suction side, particularly toward the leading edge.  At low lift coefficients, the sections are shaped so the minimum pressure occurs well back on the chord.  As the loading increases, the pressure distribution on the suction side becomes more negative and flattens out.  The section is typically designed for the pressures to be very close to the water vapor pressure along the entire forward half of the chord at the design loading and speed, leading to a flat "rooftop" shape to the pressure distribution.  At higher loadings, a leading edge suction peak forms, and the foil needs to be operated at much lower speeds to avoid cavitation.

Thickness decreases the pressure on both sides of the foil, and the shaft sections need to be thicker than the wing sections because of the higher bending moments reacted by the shaft.  This leads to cavitation starting first on the lower shaft and elbow (due to interference between shaft and wing), then spreading up the shaft and down the elbow as speed increases.

Upwind, the loading on the shaft is greater because of the higher side load from the rig.  This leads to a lower cavitation onset speed compared to downwind.

Almost all makes sense, but could you explain the second last one. Why do you think there are more side load from the rig during upwind?

Same righting moment and tighter apparent wind angle would suggest distributing wing lift more equally upwind and less at the tip for downwind with lower center of effort, and greater force. The differencies of aws should be too small compared to that awa affect  to reverse the situation.But then there is also far more boatspeed downwind, therefore more side force might still need less lift coefficient for the shaft. But as force is greater, so must be the average pressure if area remains the same, but does it really? Is there a difference in flying altitude upwind and downwind in those conditions cavitation is relevant issue? If so which has less area, upwind or down, and would that dictate the cavitation issue as well?

 

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3 hours ago, Ex-yachtie said:

Fair enough.  

 

I'll ask this in case it's already been answered.  I'm pretty skeptical about the numbers and how they are measured.  There was a moment where Ken Reed was talking about the stats, the two boats (OR and ETNZ?) had the same average speed, the same average VMG, they has sailed the same distance, but ETNZ were 400m ahead. So:

 

Do/should they calculate VMG on the average TWD, or per boat?

Do/should they exclude tacks and gybes?

I laughed when he said that.

The stats he was looking at were for the LAST LEG not the whole race.

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31 minutes ago, jaysper said:

I laughed when he said that.

The stats he was looking at were for the LAST LEG not the whole race.

Agreed...

Someone should've been in Kenny's ear telling him to read the title on the graphic. Came across looking a bit daft.

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Just now, KoW said:

Agreed...

Someone should've been in Kenny's ear telling him to read the title on the graphic. Came across looking a bit daft.

They probably did, but when you've make a major flub like that you can either ignore it and hope that not many people notice or point out your own mistake and make sure that EVERYONE noticed!

I think I would have fessed up, but Kenny might have tried the first option.

Clearly he knows what the fuck he is talking about, but he is actually pretty poor at commentating. But this was simply a case of didn't read the graphic.
Still, I got a chuckle out of it.

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1 hour ago, jaysper said:

They probably did, but when you've make a major flub like that you can either ignore it and hope that not many people notice or point out your own mistake and make sure that EVERYONE noticed!

I think I would have fessed up, but Kenny might have tried the first option.

Clearly he knows what the fuck he is talking about, but he is actually pretty poor at commentating. But this was simply a case of didn't read the graphic.
Still, I got a chuckle out of it.

Poor guy was probably reading and trusting exactly what he got fed, then had no time or inclination (as you suggest) to explain the f'up even if he did realize it shortly after. Tough gig, probably at both ends of it.

 

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