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21 minutes ago, Mozzy Sails said:

Well, thanks for your plots. 

I saw the cant data in the virtual eye, but your histograms show it so much better. 

I think max is on to something with it being linked to heel. 

One idea is more cant and leeward heel going in to the tack. Ride height would stay same but effective cant angle would decrease. Moving CoE to leeward helps heading up. 

Other idea is they are using leeward helm to balance the helm in a straight line. 

But... becuase the cant data is.out of sync it's hard to tally these two. 

I've had a look at @dorox's stats app , and something odd is going on... in every upwind beat in each race, both foils start at moderate cant and then gradually increase throughout the tack.

Wondering if the hydraulics are playing up... slow loss of pressure?

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Just a few interesting bits of the straight-line performances from today: Upwind /Downwind VMGs - race 1: Upwind /Downwind VMGs - race 2: Same story in both races actually.

Thanks to weta27's pics I have created an approximation of NZ's "BFB v2" foil. Main points: Foil area is almost the same, possibly even a smidge larger. Flaps have increased in area as

OK, it sounds like there's some interest in this topic, so here goes.   Any engineering effort starts by defining the requirements.  From this figure, it looks like the average foil area is 1.64

Posted Images

3 minutes ago, amc said:

This is quite important in terms of work done to trim the boat as moving the sails in any way requires grinding. However moving the foils to achieve trim uses battery power. So simply moving the foils means less grinding. 

That's a good point. Reliability of the FCS may be a factor as well. Now they're more confident messing with it all the time than before.

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9 minutes ago, bob202 said:

Can anyone please offer any info on the wind conditions for each race and how they differed - either the prestart measurement or notable changes during each race?

I have been quite surprised how poor the info packages are here compared to Bermuda where the wind speed was often overlayed on the graphics and changes in TWD were often at the top of the screen.

Here they seem more obsesses with the on-boat footage graphics which have tons of numbers and look fancy but which are practically pointless to most viewers

Any thoughts on the wind changes which may offer some insight into the different performances in each race?

Here you go - as reported by each boat:

Race 1:

1478580317_uwtws.png.b364029535d69bfa768e84d421482d57.png771561343_dwtws.png.88f8696a6faff7ed1b3da0993debb856.png

Race 2:

1391621769_uwtws.png.4c9ccbe91f54d9e7740e02d2d337a97d.png173528757_dwtws.png.43728789a07c0b60861b1a72f0e543b9.png

The 2nd race wasn't actually that much windier. Both teams switched to smaller jibs. I wonder if maybe ETNZ ended up with a jib too small for the conditions.

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6 minutes ago, MaxHugen said:

I've had a look at @dorox's stats app , and something odd is going on... in every upwind beat in each race, both foils start at moderate cant and then gradually increase throughout the tack.

Wondering if the hydraulics are playing up... slow loss of pressure?

The foil cant data is a bit messed up, but that change in cant angle after the tack is not new. It's part of how they accelerate and then turn upwind after the tack. 

Foil cant during tacks and jibes - race 1:

1605349431_tcant.png.122be89b63961f5a98341c80f483335f.png2095965514_jcant.png.8e27c2a4e30c888bf98666785847e48e.png

Foil cant during tacks and jibes - race 2:

79853492_tcant.png.7631d3eef095c2a39c4aa2f1ac682eb9.png1444264771_jcant.png.a0fbe3aef103dc9cb4822e362c42f297.png

The timing is messed up for ETNZ, so it looks as if they lifted the old foil out before lowering the new foil down, which is obviously not true (although would be spectacular:))

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11 minutes ago, erdb said:

The foil cant data is a bit messed up, but that change in cant angle after the tack is not new. It's part of how they accelerate and then turn upwind after the tack.

I understand that, but "both foils start at moderate cant and then gradually increase throughout the [entire] tack".

image.png.6ad71420ae4c543baa2b29314c2ce47c.png

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Speaking of tacks - it seemed obvious to me during the race that ETNZ lost a lot more during tacks than LR. However, looking at the VMG data, it's not that different between the boats.

Race 1, VMG and distance gained to the mark during tacks:

1159583089_tvmg.png.aebd38c01303d6323d4e8ffdbd7ae9aa.png2037507700_tvmgs.png.c721ea573df5e20982fa29ad79f1f7dd.png

This shows ETNZ actually lost less than LR. Maybe it was just the wind shifts that made it look like they were losing more (this data is all relative to wind direction as measured on-board, so wind shift effects are eliminated).

Race 2:

320489566_tvmg.png.3ec068673e18240520920c7350f01173.png1213815281_tvmgs.png.cc9406d51cf43d74e9e031ba0514edc6.png

In race 2, the losses are reversed, but it's actually very close in both races. It also depends on what you consider as loss. I take 0 - 20 sec VMG as reference for each boat. So if one boat has a higher straight-line VMG, it can lose more during the tack relative to its own VMG and still come out ahead of the other boat. 

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5 minutes ago, MaxHugen said:

I understand that, but "both foils start at moderate cant and then gradually increase throughout the [entire] tack".

Yeah, not always but often. I thought it was the build for the next tack. 

See below. Bit annoying that the scale includes the raised position as it makes the smaller changes harder to see!

image.thumb.png.9a0de4c0334cab4022e88e44d7184c53.png

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1 minute ago, erdb said:

Speaking of tacks - it seemed obvious to me during the race that ETNZ lost a lot more during tacks than LR. However, looking at the VMG data, it's not that different between the boats.

Race 1, VMG and distance gained to the mark during tacks:

1159583089_tvmg.png.aebd38c01303d6323d4e8ffdbd7ae9aa.png2037507700_tvmgs.png.c721ea573df5e20982fa29ad79f1f7dd.png

This shows ETNZ actually lost less than LR. Maybe it was just the wind shifts that made it look like they were losing more (this data is all relative to wind direction as measured on-board, so wind shift effects are eliminated).

Race 2:

320489566_tvmg.png.3ec068673e18240520920c7350f01173.png1213815281_tvmgs.png.cc9406d51cf43d74e9e031ba0514edc6.png

In race 2, the losses are reversed, but it's actually very close in both races. It also depends on what you consider as loss. I take 0 - 20 sec VMG as reference for each boat. So if one boat has a higher straight-line VMG, it can lose more during the tack relative to its own VMG and still come out ahead of the other boat. 

It looks to me that ETNZ lost most before the tack. Bearing of to build. 

If the VMG baseline is taken from this building phase that may skew. 

Admittedly I only have looked at the gain line distances on virtual eye. 

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9 minutes ago, MaxHugen said:

I understand that, but "both foils start at moderate cant and then gradually increase throughout the [entire] tack".

Yeah I see now that even the raised foil drops a little, but only maybe by a degree. It should be locked according to the rules, right? 

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1 minute ago, Mozzy Sails said:

It looks to me that ETNZ lost most before the tack. Bearing of to build. 

If the VMG baseline is taken from this building phase that may skew. 

Admittedly I only have looked at the gain line distances on virtual eye. 

Those graphs above start 30 sec before the tack. I don't see a big difference there either, but of course it's the average. There are better and worse tacks, and I only include a tack, if there is at least 30 sec straight line before and after the tack. It's possible ETNZ lost more when they had to tack more frequently.

If you want to get into the details -  VMG for each tack analyzed, race 1 and 2:

1992802066_tvmg0.thumb.png.fa6feb837ce1760492f4873176000b9a.png2053465124_tvmg0.thumb.png.fddd8a6119a82e3d800f4f6f98d65b2f.png

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1 minute ago, erdb said:

Yeah I see now that even the raised foil drops a little, but only maybe by a degree. It should be locked according to the rules, right? 

I haven't seen locking specified in the Rules, but then I haven't read absolutely all of it, so maybe.

Hadn't noticed the slight drop when raised until you pointed it out.

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1 hour ago, erdb said:

and the question was how that would affect righting moment.

Yes... but given the context, it was plainly a proxy for "which foil configuration will allow the harnessing of more sail power".  And I'd still contend that Mozzy and the boys' original "longer lever is better" argument is correct because both the vertical and horizontal vectors matter.

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59 minutes ago, erdb said:

It's weird that ETNZ only heels windward downwind, whereas upwind they are close to level with a slight heel to lee (on average). Any idea why they'd do that?

Perhaps it's to expose that extra bit of sail foot.  They only wanted it downwind.

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21 minutes ago, Regular Swimmer said:

Yes... but given the context, it was plainly a proxy for "which foil configuration will allow the harnessing of more sail power".  And I'd still contend that Mozzy and the boys' original "longer lever is better" argument is correct because both the vertical and horizontal vectors matter.

Yeah, but I was a bit surprised when Tom (?) said "an extra 300mm makes diddly squat difference" in discussing NZ's T foil... 0.9t at 0.3m seems worthwhile to me.

Also, NZ has ~0.5t of crew maybe 2-300mm further outboard than LR.  It all adds up.

If  they do have an issue with the foil hydraulics gradually losing pressure, it might explain why their speed is not altogether as expected.

I thought NZ should have a speed edge, and that didn't exactly leap out in those two races.  :huh:

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9 minutes ago, MaxHugen said:

I thought NZ should have a speed edge, and that didn't exactly leap out in those two races.  :huh:

This chart is one of the really big surprises

22839623-8316-4DB0-B611-7751433F6C13.thumb.png.2ab3d4fa817ead1137993b8d77bd0ffd.png

 

 

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7 minutes ago, Stingray~ said:

This chart is one of the really big surprises

22839623-8316-4DB0-B611-7751433F6C13.thumb.png.2ab3d4fa817ead1137993b8d77bd0ffd.png

 

 

Not really, in the tacking duels LRPP are slick. ETNZ seem to have to carry more speed in but built slower.

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4 minutes ago, Paddywackery said:

Not really, in the tacking duels LRPP are slick. ETNZ seem to have to carry more speed in but built slower.

Another big surprise (this from the awesome Dorox app)

1D77EEE1-21DE-40A8-95A0-FDDCCA23A4C3.thumb.png.90412d7a447496c7e7e49c298faa864d.png

Both up (lower cycles) and down TR had deeper down speeds. Almost nobody was expecting this. 

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11 minutes ago, Stingray~ said:

This chart is one of the really big surprises

22839623-8316-4DB0-B611-7751433F6C13.thumb.png.2ab3d4fa817ead1137993b8d77bd0ffd.png

 

 

Maybe the next two races will resolve the lingering speed (VMG) question.

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3 minutes ago, MaxHugen said:

Maybe the next two races will resolve the lingering speed (VMG) question.

We will get a better view the more races take place. This could be a day of considerable learning for both teams and today behind closed doors, they’ll be figuring out what to do. Minor teaks because the boats have been certified but I’m sure there's stuff happening today.

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2 minutes ago, MaxHugen said:

Maybe the next two races will resolve the lingering speed (VMG) question.

One of the greatest things about day 1 is how superb the conditions were, exactly in what we all thought was the crossover ‘sweet spot’ between the boat designs. 
 

Yes, it would be fascinating to see who has the better VMG in conditions above or below, but dang... Would love it if these gorgeous conditions continued. 

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The damage was done in R2 when LR forced ETNZ to follow into the marks they were often 8Knts slower and without a split. Disturbed air well done LR.

The impact on the  average VMG from those sections is everything. My pick is that ETNZ had very poor course management and never got the initiative and that is everything. PB was sitting at the presser just wanting to get to the Bot for a run through.

The start was a stuff up, way late, in the past races if both come over the line equal they can live there the course boundary ensures you have the initiative post 1st boundary tack. PB tacked off and they had 60m lead and they did not gain so should have stayed there.

7 seconds is tight one shift from a feather duster.

     

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3 hours ago, Stingray~ said:

Another big surprise (this from the awesome Dorox app)

1D77EEE1-21DE-40A8-95A0-FDDCCA23A4C3.thumb.png.90412d7a447496c7e7e49c298faa864d.png

Both up (lower cycles) and down TR had deeper down speeds. Almost nobody was expecting this. 

ETNZ is red - to me their speed drops seem smaller even here. Looking at the full-length data, it's only the 2nd upwind of the 2nd race when they clearly have a speed/vmg disadvantage against LR. When I averaged all tacks during the race,  ETNZ actually came out on top, which was surprising to me, too.

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One other point I forgot. Practicing with a power boat teaches you learn nothing about disturbed air. PB looked like he was processing stuff and I would suggest he had it in his mind that he could gas past them, now he realizes he has to be in clear air to get past if its even possible.   

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2 minutes ago, coercivity said:

One other point I forgot. Practicing with a power boat teaches you learn nothing about disturbed air. PB looked like he was processing stuff and I would suggest he had it in his mind that he could gas past them, now he realizes he has to be in clear air to get past if its even possible.   

I'm pretty sure he's familiar with the concept of disturber air :lol:, but I'm surprised that covering the opponent has been so successful in these AC75s. From my VPP it seemed that the polars are quite flat around the upwind angles meaning they could easily switch between low and high modes and still keep close to max VMG:

1584147114_Speedpolarcr.png.228274bd1bb5c450e8d0b37dd8100ef5.png

I thought the covered boat could easily sneak across the wind shadow if they wanted, which isn't that wide anyway at 11 deg AWA. For some reason it doesn't seem to work though. LR kept tacking just under the line of ETNZ to make sure they can't escape with a wider angle and kept them trapped in a high mode.

 

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48 minutes ago, erdb said:

I'm pretty sure he's familiar with the concept of disturber air :lol:, but I'm surprised that covering the opponent has been so successful in these AC75s. From my VPP it seemed that the polars are quite flat around the upwind angles meaning they could easily switch between low and high modes and still keep close to max VMG:

1584147114_Speedpolarcr.png.228274bd1bb5c450e8d0b37dd8100ef5.png

I thought the covered boat could easily sneak across the wind shadow if they wanted, which isn't that wide anyway at 11 deg AWA. For some reason it doesn't seem to work though. LR kept tacking just under the line of ETNZ to make sure they can't escape with a wider angle and kept them trapped in a high mode.

 

Where are you getting the 11 degree wind shadow? Sorry, I have not managed to keep up with all the info... Thanks.

 

Seems like most people never learn to use the flat tops of polars, but I would think Burling would have that down pretty well. I would guess that the affected air behind an AC75 is pretty broad given the power. I would guess the efficient rig makes it really a direction change than a speed change or turbulence, though.

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12 minutes ago, nroose said:

Where are you getting the 11 degree wind shadow? Sorry, I have not managed to keep up with all the info... Thanks.

 

Seems like most people never learn to use the flat tops of polars, but I would think Burling would have that down pretty well. I would guess that the affected air behind an AC75 is pretty broad given the power. I would guess the efficient rig makes it really a direction change than a speed change or turbulence, though.

11 degree is the AWA. I don't know how wide is the affected swath of air coming off the sails. Obviously wider than I thought...

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The no look tach would be an asset here and a bit of a pretend tach could be used so far nothing, he's thinking hard. 

and on the simulator with a bot.

In the 49'rs he takes a bit to get rolling.  

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7 hours ago, MaxHugen said:

Yeah, but I was a bit surprised when Tom (?) said "an extra 300mm makes diddly squat difference" in discussing NZ's T foil... 0.9t at 0.3m seems worthwhile to me.

Also, NZ has ~0.5t of crew maybe 2-300mm further outboard than LR.  It all adds up.

If  they do have an issue with the foil hydraulics gradually losing pressure, it might explain why their speed is not altogether as expected.

I thought NZ should have a speed edge, and that didn't exactly leap out in those two races.  :huh:

I was told about fcs pressure bleeding issues by one of the sailors a few days after Defiant scared the kids at Okahu Bay.  I was lucky enough to speak to quite a few of the various team members before Christmas, raised this issue every time, and from the responses, I think it's a thing.  

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12 minutes ago, I ride bikes said:

I was told about fcs pressure bleeding issues by one of the sailors a few days after Defiant scared the kids at Okahu Bay.  I was lucky enough to speak to quite a few of the various team members before Christmas, raised this issue every time, and from the responses, I think it's a thing.  

Aha!  Well, if we see NZ going back to their previous ACWS form with relatively stable/constant upwind cant angles, we can assume that was an issue.

Maybe. :)

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1 hour ago, MaxHugen said:

Aha!  Well, if we see NZ going back to their previous ACWS form with relatively stable/constant upwind cant angles, we can assume that was an issue.

Maybe. :)

I'm not sure this can explain it though. The cant angles in ERDBs histograms looked grouped. To me that looks like set angles, rather then a gradual rotation. I'd expect a more even distribution and less grouping. 

Plus, when you zoom in to the data, it definitely looks like step changes in cant, rather than a slow slide. (one of my annoyances with the data is that that axis should be cropped to 50-75 degrees so you can see the relevant changes). 

Also, the onboard communications they reference cant angles several time, which they never do in the ACWS. 

There is a definite trend to cant out pre-tack though. 

 


"Good cant": https://youtu.be/WRraRPnBbXY?t=5244

 

cant settings.jpg

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Sorry if it's already explained but I've tried a quick search and can't find it. What is the source of all the data we use in this analysis here? Is it possible that the data was "lightly" and deliberately modified before being made public? (to avoid mutual performance analysis by teams)

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44 minutes ago, strider470 said:

Sorry if it's already explained but I've tried a quick search and can't find it. What is the source of all the data we use in this analysis here? Is it possible that the data was "lightly" and deliberately modified before being made public? (to avoid mutual performance analysis by teams)

I believe they are using data "extracted" from VirtualEye, it's entirely possible this data has jitter in it to prevent that scenario, but equally it is likely that as it is part of the protocol that it is something the teams just accept. They will have higher resolution data internally for their own boat I'm sure.

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1 hour ago, strider470 said:

Sorry if it's already explained but I've tried a quick search and can't find it. What is the source of all the data we use in this analysis here? Is it possible that the data was "lightly" and deliberately modified before being made public? (to avoid mutual performance analysis by teams)

That's prohibited under the class rules. The source of data sent to media equipment has to be the highest quality. You can actually see how UK fixed their wind readings issues towards the Prada cup final. There are however delays introduced at various stages of data processing by VirtualEye, and it's hard to keep track of them all.

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6 hours ago, gigi said:

Does someone have acurate drawing  or 3d of foil arm? Or at least distance from foil arm datum to axis of rotation?

Not 3D, but here are the dimensions (in meter) and angles I used. The green circles on the anhedral foil indicate the geometric center of LR's foil wings based on Max's measurements.

dimensions.JPG.bd303a9a5d4c8a8bf7e58c877b11bbe5.JPG

angles2.JPG.840802371a78fd0958e76f96fb8159d3.JPG

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3 hours ago, erdb said:

Not 3D, but here are the dimensions (in meter) and angles I used. The green circles on the anhedral foil indicate the geometric center of LR's foil wings based on Max's measurements.

dimensions.JPG.bd303a9a5d4c8a8bf7e58c877b11bbe5.JPG

angles2.JPG.840802371a78fd0958e76f96fb8159d3.JPG

Thanks erdb.

Fcs cant angle; is it measured from vertical or from lowest position gravity vise? This is angle from data? 68 degrees?

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1 hour ago, gigi said:

Thanks erdb.

Fcs cant angle; is it measured from vertical or from lowest position gravity vise? This is angle from data? 68 degrees?

It is measured from a vertical line pointed ‘straight down’ from that foil arm’s canting axis hinge point, is my understanding.. erdb? 

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49 minutes ago, Stingray~ said:

It is measured from a vertical line pointed ‘straight down’ from that foil arm’s canting axis hinge point, is my understanding.. erdb? 

Yes from vertical.

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1 hour ago, 45Roller said:

Mozzys take

 

Hey Mozzy, great video again. My heel angle graphs showed it clearly, it just didn't occur to me that it's a roll tack.

Race 1 and Race 2 tacks, average heel angle (positive is leeward):

576462333_theel.png.3c96b648fd6859677e195c7e2bfabed5.png970536244_theel.png.11e375356725c11a22775d1df8d24117.png

One question, what prevents ETNZ from roll tacking without footing off? Wouldn't that still help a bit? 

Also, about canting the foil out while heeling, I'm not sure it's done to keep the boat low. You could just ride your foil deeper if you wanted to do that. I think they cant out to keep the alignment of foil and sail forces. Keeping their effective cant angle the same while heeling.

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I think the foot off is needed as slight speed build, to then shoot up.

You could run foils deeper and heel, but it would be more whetted area on the outside of the turn and you would lose righting moment. 

This allows you to heel the boat but lose less righting moment. You will still lose some with the rig going to leeward. 

I guess these boats are unlike a normal dinghy, where your righting moment increases as you heel due to the shift in centre of buoyancy. So it's kind of like recreating that. 

Edited by Mozzy Sails
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Just another thing, it's funny I didn't understand why my algorithm said ETNZ pulled the old foil out sooner than lowering the new foil during tacks. Turns out, at some point I set a limit for max cant angle at 68, above which the foil is considered "lifted". Once I raised this limit to 75, everything works again with the pre-tack cant out clearly visible:

1349582950_tcant.png.7bccd2dade73791b89acf513a49656e0.png254365308_tcant.png.e3e4c32dc5990c233bfe0ee4a01e762f.png

The dip we see in cant angle immediately after tack (especially during the first lighter wind race), could be a compensation of the windward heel the same way as increasing the cant is a compensation of leeward heel before the tack.

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I did another analysis on the T foil vs Y foil question, because it bugged me that we don't have a clear answer.

I figured the real question is not righting moment, but how  much lateral sail force you can put on the boat and still maintain balance. If lift/drag ratio is kept the same, the more heeling force you can withstand, the more driving force you have.

top2.thumb.png.9dfc46a704aa94fc08994cd3ad527fac.png

FCS cant angle (left) and Sail CoE (right) with increasing lateral sail force (horizontal axis).

Thick red line is the T foil. Since this foil can only generate lift in the direction perpendicular to the foil, as the lateral force increases, the foil needs to be canted out more, and the sails' CoE has to be lowered. This is why we see the cant angle going up gradually after ETNZ tacks, because as they accelerate, apparent wind comes forward and increases. They need to sheet in and twist out - lateral force increases, CoE comes lower. For every side force value, there is only one cant angle and CoE height that balances the boat.

You could use a Y foil the same way as a T foil - keeping the load on the foil wings always symmetric. This scenario is shown by the green line, running on top of the red line. 

However, differential flap settings on a Y foil allow a much wider range of cant angles. This is shown by the shaded area between the minimum possible cant (blue) and maximum possible cant (magenta) lines. This also gives you more freedom in setting the sails' CoE at different heights (right graph).

Looking at the righting moment the same way reveals why you can't tell which foil provides higher RM without specifying a lateral force. This is because CoE can change and with that cant angle changes as well

rm.png.b35dfb5de4c47d6736e55f46fbfba84a.png

What you can see here, is that all the way to the maximum lateral force, the Y foil can generate more righting moment with differential flap settings, but the RM limit is the same at the max lateral force predicted by the VPP at 24kt TWS, target upwind TWA (isn't it interesting that the lines meet there?).

The higher RM at lower lateral forces allows setting the sails' CoE higher for a potentially more efficient (less twisted) sail shape. But there is a downside: if you use differential flaps, the foil wing lifts will not be symmetric potentially causing a big vortex / more drag, and the foil wings need to be larger, since the size has to match the max wing load.

Inside (left) and outside (right) wing loads with increasing lateral force:

559499761_insidecr.png.8e0c8851fbb2ff851f5513dc32948e38.png1182330005_outsidecr.png.bc6c30cf97ffd150c2064a431bf70655.png

The red line is lift on a T foil wing, and the green is what you would have if you used the Y foil the same way as the T foil. As you can see, even if you cant the Y foil the same way as a T foil (so lift is symmetric), you would need to generate more lift per wing due to the anhedral angle and because the wings are not perpendicular to the overall lift vector. Any time you deviate from the cant angle that goes with symmetric loading, the assymetry is even worse. My guess is that they don't deviate too far from the green line, but there is definitely more flexibility in cant angle.

Finally the relationship between can angle and wing lift for the hard core nerds :D:

In the above graphs, blue line shows the minimum possible cant and magenta shows max possible cant. So for a given side force, wing forces change like this:

852874176_insidecrwarrow.png.3c909c02a7c66da1fa7dafe5bf176bb2.png865424560_outsidecrwarrow.png.2725db142ec94d0cacb5d26272245922.png

With increasing cant, the load on the inside wing goes down, whereas the load on the outside wing increases. This is caused by how well each wing is lined up with the overall force the foil needs to generate:

arrows.thumb.JPG.a779968604b1a15feb1e2b879683e270.JPG

Pink shows the required direction of the overall force, red and green are the individual wing lifts. You can actually achieve this same force distribution either by differential flap settings or by adjusting pitch and yaw angles accordingly.

Technical details:

Starting parameters: lateral sail force ranges between 30 to 50 kN - this is about the same range my VPP suggested for upwind angles from 8 to 24 kts TWS.

Rudder vertical force was kept zero (this is certainly not true in reality, but had to simplify things). With rudder vertical zero, vertical foil force = weight = 74.2 kN.

FCS cant angle was limited between 50 and 70 degrees, and maximum lift generated by a wing half was 60kN, about 35% more than what my VPP suggested for the T foil.

 

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8 hours ago, Xlot said:

Really really good. Now it’s up to some French speaker to provide a summary. Otherwise, I’ll see what I can do tomorrow

Few points:

- Started to work with TNZ in 2010 after he build a VG boat for Dick in NZL.
- He is working half time for TNZ given his other project, more as adviser than coordinator. It still takes time to suggest and critics ideas to have some depth in them.
- He thinks that they are too many in the design team (~25). Less people are more efficient. Many people are specialist and GV has a global vision.
- 5-6y ago, he got a discussion about a 40feet performance boat. Ray Davis didn't like the keel, GV suggested to put the weight in the foils instead, some laugh. But after first analysis, it proves to be 50% faster than VG boats. Boat is not build because too expensive.
- After the win in Bermuda, concept comes back. They make a simple model for simulation and it seems to work. GV would have preferred 2 safrans but not optimal for safety reason.
- They wanted a rule tight enough to limit differences (and performance differentiation). Rule took time to elaborate.
- Relieved that UK build small boat quickly and it was working.
- GV doesn't like stability restriction on the hull. Quickly led to a centre hull of a trimaran. Flat transom is providing stability hence the square shape.
- No big evolution between boats #1 and #2, went even more towards multi.
- Important to have easy take off and quickly reduce wetted surface.
- Boat is a mix between static and dynamic equilibrium. Foils bring stability. Have to bear away between equilibrium. Initially UK found that boat capsize at transition. GV reckon the approach had more risks than UK.
- Second boat more aero, first more hydro focused.
- Boat less demanding than AC50 on the sailors. Sailors extenuated at end of race during AC50.
- Maybe in future boat might create their own energy (for foil canting system).
- GV was thinking that there would be differences between first gen but much reduced for second gen, as it appears to be.
- T foil has less wake drag, but hydro logic is more in favor of Y to have max separation, reduces drag from shaft. Both can work well. For simplicity and mechanics, they liked T. They designed both then chose. GV is in favor of pushing the philosophy to the end rather than change boat to the winning formula (with reference to VG).
- Symmetry only at the end, rarely the case before the match.
- Hump on the arm is allowed by T config (not possible in Y). It's something related to gauge and not hydro. Don't copy that, not so interesting.
- Won't comment on the match favorite/result
- Horizontal organisation. No real boss, working for small structure, quick exchanges. When engaged, they don't come back on design to respect production lead time. He doesn't see that in France as people want changes that delay production. No delay in prod, advantage to produce in house.
- Less design on simulator than last time. More fundamental design. AI is everything but intelligent, and mainly artificial (need to understand and no just trust the machine). Need to look around, paragliding, voltige plane, ... to find the right mix. Impressed by how much info is available easily.
- GV like to produce first design quickly and have global vision.
- Discussions VG.

 

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On 3/10/2021 at 10:51 PM, erdb said:

Speaking of tacks - it seemed obvious to me during the race that ETNZ lost a lot more during tacks than LR. However, looking at the VMG data, it's not that different between the boats.

Race 1, VMG and distance gained to the mark during tacks:

1159583089_tvmg.png.aebd38c01303d6323d4e8ffdbd7ae9aa.png2037507700_tvmgs.png.c721ea573df5e20982fa29ad79f1f7dd.png

This shows ETNZ actually lost less than LR. Maybe it was just the wind shifts that made it look like they were losing more (this data is all relative to wind direction as measured on-board, so wind shift effects are eliminated).

Race 2:

320489566_tvmg.png.3ec068673e18240520920c7350f01173.png1213815281_tvmgs.png.cc9406d51cf43d74e9e031ba0514edc6.png

In race 2, the losses are reversed, but it's actually very close in both races. It also depends on what you consider as loss. I take 0 - 20 sec VMG as reference for each boat. So if one boat has a higher straight-line VMG, it can lose more during the tack relative to its own VMG and still come out ahead of the other boat. 

The best way to analyse the efficiency of the tacking would be to draw a straight horizontal  line across the graph and measure the positive area above the line (distance gained to windward ) and subtract that from the area below the line ( distance lost to windward). This will tell you how good the tacking is rather than just looking at the minimum speed in the tack. 

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9 minutes ago, oatsandbeans said:

The best way to analyse the efficiency of the tacking would be to draw a straight horizontal  line across the graph and measure the positive area above the line (distance gained to windward ) and subtract that from the area below the line ( distance lost to windward). This will tell you how good the tacking is rather than just looking at the minimum speed in the tack. 

I think this is pretty much what I'm doing except I don't use  area above the graph.

The first graph is VMG not speed, since that's what matters. On the 2nd graph, solid lines are area under the VMG curves. The dotted straight lines are determined by VMG during the first 20 sec before tack omitting the last 10 sec since that's when boat tends to fall off to build speed and then head up to start the tack. So the dotted lines show how much distance the boat would keep gaining against the wind if it didn't tack. The solid lines show the actual distance gained, which is the area under the VMG curve. The difference between the dotted and solid lines at 30 sec after tack is shown as lost distance (compared to their own pre-tack VMG) in the lower right corner.

Why would you subtract the area above the line from the area below the line? And how do you define area above the line? What's the ceiling? Regardless how you define that, I think that wouldn't be correct, basically you'd arteficially double the differences in distance gained/lost.

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Sorry I missed the bit about how to define the baseline. First I would try a single continuous line as this is simple and it would define the start of the tack as when the vmg moves above this in the luff. The end of the tack would be when the vmg returned to this value.

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1 hour ago, oatsandbeans said:

The area above the line is distance gained to windward in the first phase of the tack which is a gain. (The head up) . This quickly goes negative as the boat goes through the wind bears off and the speed drops. 

No, it's the area under the VMG curve which is distance gained to windward. Just think about it - the higher the VMG, the higher the VMG line, the higher the area under curve and the more distance you gain.

32 minutes ago, oatsandbeans said:

Sorry I missed the bit about how to define the baseline. First I would try a single continuous line as this is simple and it would define the start of the tack as when the vmg moves above this in the luff. The end of the tack would be when the vmg returned to this value.

I'm not really sure what you mean. My baseline is the dotted line on the "distance gained" figure. That's how much distance the boat would keep gaining if it continued to sail as it did in the first 20 sec before tack. Click on the image to see it in big, you can see how the solid line momentarily goes above the dotted at the time of the tack when the boat goes head to wind, then falls below the dotted line as it accelerates out of the tack.

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@Lakrass: excellent summary. Minor points, safrans=rudders, also I understood foil arm spats house ballast

Generic notes: he’s 50, strikingly subdued (with a touch of depression?) especially compared with his flamboyant Argentine homologues. Confirming the cliché, even after 10 yrs his English accent is atrocious.

Relevant to anybody intending to poach him for AC37: his role is what in the aero industry’s called a “configurator”, defining the overall characteristics of a project, not interested in specific details or in the Engineering Manager role

He and his associates do not have an office, they all work from home!

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Data from yesterday and an interesting discovery regarding wind direction reported by ETNZ.

Kenny was perplexed when Pete told him after race 1 that he was happy with how the boat sailed. At frst glance, Pete was actually right.

VMG in race 3:

1253554530_uwvmg.png.c504d9eb872314657caf8d230ccd0bfa.png1103485559_dwvmg.png.a7d270de94604e4f038554b1a81de177.png

So how the hell did they not win the race? Again, looking at the time spent on the favored tack shows that ETNZ did much worse than LR.

favtack.png.d301e9e946457ca016d46dbc179d5a7a.png

OK, so they were pushed again out of phase by LR, right? The funny thing is that data from race 4 looks exactly the same. Nice advantage in both upwind and downwind VMG for ETNZ, but constantly sailing out of phase:

favtack.png.f7d3fc87c3e2a08b901efadc3fb0df84.png

So this made me very suspicious, especially, because even in the ACWS, ETNZ always seemed to sail out of phase.

I went to look at virtual eye, and sure enough, every time ETNZ tacks, the advantage line angle changes indicating that the wind just turned against them. I assume the advantage line angle is derived as an average of TWD reported by the two boats, but it seems calibration is off on TR, and they always pull the reported TWD against themselves (or they're so fast, they bend space-time. Should we call it apparent gravity?)

What's funny is that it dictates this story line that ETNZ is faster straight line, but they lose a lot more in tacks. This may be true to some extent, but it's exaggerated by this calibration error. When they tack, the angle of the advantage line changes and suddenly shows ETNZ falling behind. As the two boats come closer and lateral separation decreases, the effect of this angle bias goes away, and suddenly ETNZ looks much better.

Unfortunately, this calibration error affects VMG and TWA data as well, so their superior VMG shown above is at least partially caused by this.

ETNZ is definitely faster upwind in straight line, but the TWA data may be incorrect showing similar angles for LR and ETNZ:

18391986_uwbs.png.00c961b66670d56e85e7081eea9c6327.png1694228709_uwtwa.png.8f0bc802e2ffed2a6f7c631e8c28c523.png

In reality, ETNZ is probably faster, because they sail a bit lower (in general). So if you're watching the races, don't pay attention to the advantage lines when boats are on opposite sides of the course, it's only correct when they are close together. 

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47 minutes ago, erdb said:

In reality, ETNZ is probably faster, because they sail a bit lower (in general). So if you're watching the races, don't pay attention to the advantage lines when boats are on opposite sides of the course, it's only correct when they are close together. 

The data displayed on the Live broadcast is often suss... I usually keep an eye on VMG, and I've watched advantage reducing despite higher VMG at times.  :huh:

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2 minutes ago, MaxHugen said:

The data displayed on the Live broadcast is often suss... I usually keep an eye on VMG, and I've watched advantage reducing despite higher VMG at times.  :huh:

I'm pretty sure there is only one set of data reported and that's what they show during broadcast and then post on virtual eye. It's all fake news! :D

Losing distance despite having higher VMG could actually happen if a boat is on on the wrong side of a shift since VMG is reported against the boats own TWD. The problem is that the shifts are not real, but caused by ETNZ's instruments.

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1 hour ago, Xlot said:

I understood foil arm spats house ballast

That's one opinion, but I don't see why they would move very useful ballast inboard and reduce RM!

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3 minutes ago, MaxHugen said:

That's one opinion, but I don't see why they would move very useful ballast inboard and reduce RM!

Ok, but that’s what I heard him say. So, unless I got it wrong ...

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14 minutes ago, MaxHugen said:

The data displayed on the Live broadcast is often suss... I usually keep an eye on VMG, and I've watched advantage reducing despite higher VMG at times.  :huh:

Yeah this mate, the numbers don't seem to add up at all

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Just now, Xlot said:

Ok, but that’s what I heard him say. So, unless I got it wrong ...

No, you're right, someone was discussing this as a possible reason for the spats/gaiters/lumps/growths, I forget where it started. :)

My guess is that it's to reduce the amount of spray the crew cop in the face.

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Interesting analysis, especially when Federico Albano analyzes the numbers (01:14:59) 

His didn't understand why LR was gaining upwind in  Race 3 despite having -1.13 knots in average  speed and -0.65 knots in VMG (despite having a slightly better angle: - 0.43 TWA). He didn't understand why LR sailed 1.133 m less than ETNZ with those numbers. Using GPS data, his answer is that LR has much less leeway than ETNZ. 

Here his graphic

LRperformanceupwind.thumb.jpg.6a0359569596e4ae3e420d5b6ac10573.jpg

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3 minutes ago, Zaal said:

Interesting analysis, especially when Federico Albano analyzes the numbers (01:14:59) 

His didn't understand why LR was gaining upwind in  Race 3 despite having -1.13 knots in average  speed and -0.65 knots in VMG (despite having a slightly better angle: - 0.43 TWA). He didn't understand why LR sailed 1.133 m less than ETNZ with those numbers. Using GPS data, his answer is that LR has much less leeway than ETNZ. 

Here his graphic

LRperformanceupwind.thumb.jpg.6a0359569596e4ae3e420d5b6ac10573.jpg

 

3 minutes ago, Stingray~ said:

The wind data comes from identical instrumentation, at the top of the masts, right? 

Yeah, the data comes from the boats. The problem is that they can only measure apparent wind speed and angle, and they calculate true wind direction and speed back from that using boat speed. If any of these instruments is slightly off, the data will be biased as well. This was probably the case all along, but now we have two boats with almost identical performances and we had 4 races with steady winds, which made it easy to notice these small errors. Big wind shifts and puffs would hide these errors.

I don't buy the leeway story either, because I know the compass data is messed, up too. :wacko:

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Just for fun, I recalculated race 4 by replacing ETNZ's wind data with LR's data. It's not correct either, because they could be in different winds, but luckily the wind was very steady. Anyway, just to see what difference it makes:

Upwind, ETNZ is faster, but now it's obvious they point lower for almost identical VMG and AWA:

1773931687_uwbs.png.3636b2d47b1810e00df2d97f3cb9a22b.png355143164_uwtwa.png.ebd898eab7df7ff62fc2e7abbdf0dd81.png

1046185879_uwvmg.png.447cf949def24f39be9c9518e2367f19.png1869281429_uwawa.png.69ffcb4d7261a18ac7774cd1fc298ea8.png

Their downwind performances got much closer, too. Using ETNZ's wind data it always seemed ETNZ was far superior downwind, but it's because their instruments think they are in a header all the time. Here it is with LR's wind data. ETNZ is faster, but sails higher for an almost identical VMG:

1857952216_dwbs.png.f194572522fa63164388b5b8cd4803fb.png683333071_dwtwa.png.ac569fdf84878aac4d48e9b02fbd03e7.png195171564_dwvmg.png.2f280fe903f2486c322731a9867e9933.png809027667_dwawa.png.bbfd79aa5034b5c7d510a4670e380017.png

Can anyone send a message to Kenny / Nathan / Shirley about this? The whole narrative about differences in performance is driven by bad wind data from ETNZ. The truth is that in terms of VMG, the boats are basically identical both upwind and downwind. ETNZ is faster, LR sails closer to the mark.

 

Oh and forgot to add, the "on favored tack" data looks much better now for ETNZ. LR is still gaining more, which may indicate that their instruments are also a little off just in the other direction.

factack.png.7324c249c208703cdfe94082880e989b.png

 

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3 minutes ago, erdb said:

Just for fun, I recalculated race 4 by replacing ETNZ's wind data with LR's data. It's not correct either, because they could be in different winds, but luckily the wind was very steady. Anyway, just to see what difference it makes:

Upwind, ETNZ is faster, but now it's obvious they point lower for almost identical VMG and AWA:

1773931687_uwbs.png.3636b2d47b1810e00df2d97f3cb9a22b.png355143164_uwtwa.png.ebd898eab7df7ff62fc2e7abbdf0dd81.png

1046185879_uwvmg.png.447cf949def24f39be9c9518e2367f19.png1869281429_uwawa.png.69ffcb4d7261a18ac7774cd1fc298ea8.png

Their downwind performances got much closer, too. Using ETNZ's wind data it always seemed ETNZ was far superior downwind, but it's because their instruments think they are in a header all the time. Here it is with LR's wind data. ETNZ is faster, but sails higher for an almost identical VMG:

1857952216_dwbs.png.f194572522fa63164388b5b8cd4803fb.png683333071_dwtwa.png.ac569fdf84878aac4d48e9b02fbd03e7.png195171564_dwvmg.png.2f280fe903f2486c322731a9867e9933.png809027667_dwawa.png.bbfd79aa5034b5c7d510a4670e380017.png

Can anyone send a message to Kenny / Nathan / Shirley about this? The whole narrative about differences in performance is driven by bad wind data from ETNZ. The truth is that in terms of VMG, the boats are basically identical both upwind and downwind. ETNZ is faster, LR sails closer to the mark.

 

Oh and forgot to add, the "on favored tack" data looks much better now for ETNZ. LR is still gaining more, which may indicate that their instruments are also a little off just in the other direction.

factack.png.7324c249c208703cdfe94082880e989b.png

 

Good work @erdb, as usual!

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3 minutes ago, erdb said:

The truth is that in terms of VMG, the boats are basically identical both upwind and downwind. ETNZ is faster, LR sails closer to the mark.

Watching race 4 might be as good an indication of comparative upwind/downwind VMG as we'll get. I think they were far enough apart to not be sailing in a wind shadow etc, so overall, NZ looks like they had a slight VMG advantage upwind, and a bit more downwind.

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57 minutes ago, MaxHugen said:

No, you're right, someone was discussing this as a possible reason for the spats/gaiters/lumps/growths, I forget where it started. :)

My guess is that it's to reduce the amount of spray the crew cop in the face.

Not sure about the translation or what is meant be 'gauge', but is it not saying the spats are allowed because of the of the T foil?

To my mind this is likely true in that moving some mass to the bottom of the rule box allows some other material to be moved above the waterline. Reducing volume in the foils. 

They definitely have foil systems in the spat as well, as why have a window in it otherwise?

I also dont think they are for spray as they dont seem to be in any spray. The spray is all shed by the lip below. 

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8 minutes ago, MaxHugen said:

Watching race 4 might be as good an indication of comparative upwind/downwind VMG as we'll get. I think they were far enough apart to not be sailing in a wind shadow etc, so overall, NZ looks like they had a slight VMG advantage upwind, and a bit more downwind.

Yeah, I agree, but those differences in VMG are tiny. The gap only grew between them when LR messed up that jibe. Just imagine how exciting the racing would be on a shifty-puffy course. The lead could change with every shift.

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5 minutes ago, erdb said:

Yeah, I agree, but those differences in VMG are tiny. The gap only grew between them when LR messed up that jibe. Just imagine how exciting the racing would be on a shifty-puffy course. The lead could change with every shift.

Yeah, not much in it upwind. But NZ's gains downwind were decent:

image.thumb.png.89f912a5052349e9c542cf2e7ffcf247.png

Finish was 1:03.

Will be interesting to how they both perform in a high wind range, if that should come to pass.

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29 minutes ago, Mozzy Sails said:

Not sure about the translation or what is meant be 'gauge', but is it not saying the spats are allowed because of the of the T foil?

To my mind this is likely true in that moving some mass to the bottom of the rule box allows some other material to be moved above the waterline. Reducing volume in the foils. 

They definitely have foil systems in the spat as well, as why have a window in it otherwise?

I also dont think they are for spray as they dont seem to be in any spray. The spray is all shed by the lip below. 

I did a very rough estimate of what the foils would weigh (in steel), plus the "boot" (section of foil arm connected to foil), plus a bulb shell in steel and filled with lead, less 10% volume for actuator (I think)... seemed the bulb was large enough, together with foil etc, to get up around the 900 kg mark.

The SVG file I used for this got corrupted during a storm unfortunately, and I didn't have a backup. :(

It was v1 of the BFB though.

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FWIW, here's a comparison of NZ and LR foils at 30 knots, and at varying cant angles. The target load at 70,000N allows for some lift from the rudder foil, CL and CD vals are from my foil so undoubtedly higher in reality, etc. However, these numbers are probably sufficient for a rough comparison .

Both foils had flap adjusted (to 0.01°) to match Load with Vertical force (FZ), at 22° cant. "Net AoA" is an aggregation of foil AoA, leeway AoA, and flap angle.

Observations:
LR has ~3.8% more drag
LR has ~2.2% more Lateral force (FY)
LR is at 0° foil Aoa, and slightly negative flap, at just 30 knots.

Might be interesting to have a look at differential flap settings for LR later...

image.thumb.png.f32b03fce31b99f49718f86b9b921c2c.png

image.thumb.png.c07c5f9af912beb3a4f1bd278aba32ea.png

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38 minutes ago, MaxHugen said:

Yeah, not much in it upwind. But NZ's gains downwind were decent:

image.thumb.png.89f912a5052349e9c542cf2e7ffcf247.png

Finish was 1:03.

Will be interesting to how they both perform in a high wind range, if that should come to pass.

Yes, if you look at the histogram, ETNZ does have another gear downwind, but their average came out close to LR's, but this analysis only includes straight line, their jibes could be better, too.

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1 hour ago, erdb said:

Just for fun, I recalculated race 4 by replacing ETNZ's wind data with LR's data. It's not correct either, because they could be in different winds, but luckily the wind was very steady. Anyway, just to see what difference it makes:

Upwind, ETNZ is faster, but now it's obvious they point lower for almost identical VMG and AWA:

1773931687_uwbs.png.3636b2d47b1810e00df2d97f3cb9a22b.png355143164_uwtwa.png.ebd898eab7df7ff62fc2e7abbdf0dd81.png

1046185879_uwvmg.png.447cf949def24f39be9c9518e2367f19.png1869281429_uwawa.png.69ffcb4d7261a18ac7774cd1fc298ea8.png

Their downwind performances got much closer, too. Using ETNZ's wind data it always seemed ETNZ was far superior downwind, but it's because their instruments think they are in a header all the time. Here it is with LR's wind data. ETNZ is faster, but sails higher for an almost identical VMG:

1857952216_dwbs.png.f194572522fa63164388b5b8cd4803fb.png683333071_dwtwa.png.ac569fdf84878aac4d48e9b02fbd03e7.png195171564_dwvmg.png.2f280fe903f2486c322731a9867e9933.png809027667_dwawa.png.bbfd79aa5034b5c7d510a4670e380017.png

Can anyone send a message to Kenny / Nathan / Shirley about this? The whole narrative about differences in performance is driven by bad wind data from ETNZ. The truth is that in terms of VMG, the boats are basically identical both upwind and downwind. ETNZ is faster, LR sails closer to the mark.

 

Oh and forgot to add, the "on favored tack" data looks much better now for ETNZ. LR is still gaining more, which may indicate that their instruments are also a little off just in the other direction.

factack.png.7324c249c208703cdfe94082880e989b.png

 

There is something weird going on with the virtual eye VMG data.  Often the VMG on one of the two boats is considerably better than the other but the gain line is not changing in line with this  I wonder whether boat yaw crabbing behaviour may explain some of this.  I presume VMG is calculated from boat angle to mark and boat speed rather than the GPS data.  

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3 minutes ago, MaxHugen said:

FWIW, here's a comparison of NZ and LR foils at 30 knots, and at varying cant angles. The target load at 70,000N allows for some lift from the rudder foil, CL and CD vals are from my foil so undoubtedly higher in reality, etc. However, these numbers are probably sufficient for a rough comparison .

Both foils had flap adjusted (to 0.01°) to match Load with Vertical force (FZ), at 22° cant. "Net AoA" is an aggregation of foil AoA, leeway AoA, and flap angle.

Observations:
LR has ~3.8% more drag
LR has ~2.2% more Lateral force (FY)
LR is at 0° foil Aoa, and slightly negative flap, at just 30 knots.

Might be interesting to have a look at differential flap settings for LR later...

image.thumb.png.f32b03fce31b99f49718f86b9b921c2c.png

image.thumb.png.c07c5f9af912beb3a4f1bd278aba32ea.png

What complicates it further is the cant vs differential flaps and loads on LR's foil (see my above post somewhere up there). What that does with 3D flow, vortices and induced drag could have a greater impact than friction drag.

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2 minutes ago, Apterix said:

There is something weird going on with the virtual eye VMG data.  Often the VMG on one of the two boats is considerably better than the other but the gain line is not changing in line with this  I wonder whether boat yaw crabbing behaviour may explain some of this.  I presume VMG is calculated from boat angle to mark and boat speed rather than the GPS data.  

The VMG data is calculated against true wind direction as measured by the boat. Otherwise, the VMG would keep changing depending on where they are on the course. The gain line angle changes with wind direction - which is good, that's how you'd see the effect of a shift. A boat could have higher VMG against its own wind and still lose if they sail out of phase with the shifts. The problem is that ETNZ's instruments are messed up, so they always sail on a header basically, and the advantage line is screwed up because of this, too.

I guess it's convenient for them that their opponents can't get accurate data :o.

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18 minutes ago, erdb said:

What complicates it further is the cant vs differential flaps and loads on LR's foil (see my above post somewhere up there). What that does with 3D flow, vortices and induced drag could have a greater impact than friction drag.

I did this study to see what effects differential might make. So, under the same conditions, I increased the leeward foil vertical lift from 37,500 to 46,000N, by adding flap from -0.4, to 2°.

To get the same net Vert force, I had to shift windward foil flap from -0.4 to -2.50°. This would move the CE-FZ a bit further outboard, but not by much really.

Drag increase was negligible, from 1330 to 1336, which I didn't expect.

But lateral force plummeted from 28,994 to 24,203N - a drop of ~16.5% !

I think they have Vert force to spare at low drag cost, they may be more likely to increase lift on the windward foil for more lateral force?

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