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      A Few Simple Rules   05/22/2017

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richardwangphotography

Foiling Upwind - Talking with ETNZ's prinicple structural engineer

46 posts in this topic

CC120913-027-Giovanni-Belgrano-e13524077

 

Earlier tonight I a conversation with Giovanni Belgrano, the principle structural engineer for ETNZ.

 

I asked him about the "Holy Grail of the AC72" - foiling upwind.

 

Belgrano said that for slight periods ETNZ does foil upwind. But it is not consistent. "Sometimes it feels good. Very stable. And sometimes it's is very unstable."

 

Then he said something very surprising.

 

He said that foiling upwind is not important and not necessarily desirable, the reason being the narrowness of the course.

 

Belgrano reasoned that while foiling upwind you can't point as high and that boat will slide severely sideways.

 

That any gain you have in speed while foiling upwind is negated by causing you to possibly go out of bounds. And so as to not go out of bounds, you'll have to tack more often which will slow you down.

 

Belgrano continued, "If there was no out of bounds, we would certainly be foiling upwind."

 

As an aside, Belgrano also mentioned that ETNZ will soon break 3.5 times true wind speed.

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Thank you. I suspect this may have been obvious to others, but he really did say that VMG is better while foiling upwind. It's only the narrowness of the course that obviates its usefulness.

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We have known for awhile that both OR and ET have been able to foil upwind but the question always was should they?

 

There's your answer.

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as i recall the consencus of the chat on here was prety much as set out above?

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I wonder if the "chants remark" about 3.5x twspd is desined more to cast a tyny shaddo over J Spittles holiday than to enlihgten us.

 

Personelly I think ill wate til it happens to get all ecxitered about it....

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backed up by GD's constant refrain

 

that this early in the design cycle

 

small percentage gains are easy to find

 

and at these speeds, that's extra knots of boatspeed

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

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I wonder if the "chants remark" about 3.5x twspd is desined more to cast a tyny shaddo over J Spittles holiday than to enlihgten us.

 

Personelly I think ill wate til it happens to get all ecxitered about it....

 

The whomper is on the way.

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I wonder if the "chants remark" about 3.5x twspd is desined more to cast a tyny shaddo over J Spittles holiday than to enlihgten us.

 

Personelly I think ill wate til it happens to get all ecxitered about it....

 

The whomper is on the way.

Says nothing about top wind speed potential to my non-expert thinking. 3.5xtwspd would surely ventilate the foils at high wind speeds. But pretty devastating if achievable for low to moderate wind speeds where the multiplied speed was still within the cavitation limits of foils as we know them.

 

GD's comment about small percentage gains translating into knots gained equally applies to all the other teams, including OR.

 

I think too it's reasonable to add a percentage of game playing to GB's comment.

 

So I'm in the wait and see camp on this

 

meant to say - Nice secret squirrel work by richardwangphotography

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We may yet get back to the previous maximum wind speeds - once AR is spanked by LR in the QFs, nothing to stop ETNZ and LR voting them back in.

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

 

If they are seriosu about this comment, I believe it will be at lower boat speeds.

From a casual observation of the performance metrics of ETNZ in the racing, the top speed seems to hit a saturation point where the extra boat speed per knot of wind starts to really drop off.

 

Personally, I am fairly sceptical about getting 52 knots of boat speed out of 15 knots of wind.

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

 

If they are seriosu about this comment, I believe it will be at lower boat speeds.

From a casual observation of the performance metrics of ETNZ in the racing, the top speed seems to hit a saturation point where the extra boat speed per knot of wind starts to really drop off.

 

Personally, I am fairly sceptical about getting 52 knots of boat speed out of 15 knots of wind.

42 knots in 12 knots of breeze may be somewhat achievable though.

 

Upgraded wing could be a 'game changer' though

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

 

If they are seriosu about this comment, I believe it will be at lower boat speeds.

From a casual observation of the performance metrics of ETNZ in the racing, the top speed seems to hit a saturation point where the extra boat speed per knot of wind starts to really drop off.

 

Personally, I am fairly sceptical about getting 52 knots of boat speed out of 15 knots of wind.

42 knots in 12 knots of breeze may be somewhat achievable though.

 

Upgraded wing could be a 'game changer' though

How many sets of foils have ETNZ used?

I suspect that a new set of super sexy foils might be what is needed to get 42 knots in 12 knots of breeze.

My hunch is that all of the wings generate plenty of power to drive these boats to really high speeds. Possibly even enough power to overcome any extra drag that one wing would have over another (to a certain extent at least).

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As pointed out in the other thread there are ways to design the foils to eliminate the biggest cause of upwind leeway-the "V". First Team to do it will win (if they keep it secret until September). I'll bet foiling upwind w/o excessive leeway is topic #1 in R&D these days.

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The whomper is on the way.

Yes, but in addition, some Ngati Porou kaumatua are insisting they put an East Coast taniwha in with the ones from Waikato.

 

I am not too comfortable with that. Taniwha are like iwi. And it is already crowded in the taniwha tank at the back of the starboard hull.

 

Besides, they will not be releasing any taniwha unless OR gets well in front.

 

By the time the contest is over there may not be cordial relations between Waikato and Ngati Porou taniwha.

 

Also, Ray Davies (who does the feeding) had better watch his fingers.

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We may yet get back to the previous maximum wind speeds - once AR is spanked by LR in the QFs, nothing to stop ETNZ and LR voting them back in.

 

This is an excellent suggestion. It would be one hell of a way to rattle Oracle's daggs.

 

So you are suggesting ETNZ and LR, once AR is out of the way, could lock in higher wind limits which will remain once LR is gone because OR and ETNZ would be in a stalemate voting wise?

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We may yet get back to the previous maximum wind speeds - once AR is spanked by LR in the QFs, nothing to stop ETNZ and LR voting them back in.

This is an excellent suggestion. It would be one hell of a way to rattle Oracle's daggs.

 

So you are suggesting ETNZ and LR, once AR is out of the way, could lock in higher wind limits which will remain once LR is gone because OR and ETNZ would be in a stalemate voting wise?

 

I think it has to be a majority including the Defender?

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^

More than that: iirc both Defender and CoR must first agree to a change, then majority vote

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^

More than that: iirc both Defender and CoR must first agree to a change, then majority vote

 

hmm, that will sober up the kiwi fanbass

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

OK sneaks, u may be right. Please be reminded how important the go fast bolt on bits are for ETNZ in their champagne.

But.... wot iff someone was somehow to reduce drag on their boat by more than 3%. And conversely they also managed to wring another 4% out of a revamped wing, plus say 4% improvement in foil drag/lift, plus a 10% increase in AC wind limit over the LV limit= ay around 15% overall speed diff improvmnts.

All hipotheatrical i know but I think thats wot the ETNZ chief engineer Giovanni Belgrano was referring to maybe? its a kiwi trait , but its great to get an honest answer aint itt? ....or maybe its an Italian trate?

Cheers till Sept 7. Go the kiwi guys in the youth worlds...its gonna be so tight to call.

K

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

 

ETNZ hit (from memory) about 41 knots on the final reech today, in maybe 13 knots TWS?

 

Thats nearly 3.2 x TWS

 

If it woz only 12 knots TWS, its over 3.4 x TWS ! ! !

 

So unless they are close to a seeling corzed by the lorz of

 

fizzicks and the limitayshuns of the consepts they are committed to

 

Maybe they will get up to 3.5, even in a bit mor breez?

 

GD iz on rekord az saying that, this tym round, heez been plezantly

 

surprized how well actewal data has conformed to the predickshuns

 

of his boffinz, when theyv implemented improovments.

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

 

ETNZ hit (from memory) about 41 knots on the final reech today, in maybe 13 knots TWS?

 

Thats nearly 3.2 x TWS

 

If it woz only 12 knots TWS, its over 3.4 x TWS ! ! !

 

So unless they are close to a seeling corzed by the lorz of

 

fizzicks and the limitayshuns of the consepts they are committed to

 

Maybe they will get up to 3.5, even in a bit mor breez?

 

GD iz on rekord az saying that, this tym round, heez been plezantly

 

surprized how well actewal data has conformed to the predickshuns

 

of his boffinz, when theyv implemented improovments.

Ole if its true S! GD is a straight shooter. So is his engineer GB. Same with DB They seem to be singing from the same hymnbook about the next layer of improovmince. Only GB has actually quantified the speed parameter.

BTW did you see OR latest near wipout on video , same as ETNZ, but saved by the jib release. Lucky. Whew!

K

Looks lke a duck. Sounds like a duck. F....k. Its a duck. Goes like shit.

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Yep. One mighty fast duck!!

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Wind was obviously up significantly for the last leg.

But a fascinating contrast to them dawdling along at times under 20kt for last leg on the windy day when they hit 47kt.

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

OK sneaks, u may be right. Please be reminded how important the go fast bolt on bits are for ETNZ in their champagne.

But.... wot iff someone was somehow to reduce drag on their boat by more than 3%. And conversely they also managed to wring another 4% out of a revamped wing, plus say 4% improvement in foil drag/lift, plus a 10% increase in AC wind limit over the LV limit= ay around 15% overall speed diff improvmnts.

All hipotheatrical i know but I think thats wot the ETNZ chief engineer Giovanni Belgrano was referring to maybe? its a kiwi trait , but its great to get an honest answer aint itt? ....or maybe its an Italian trate?

Cheers till Sept 7. Go the kiwi guys in the youth worlds...its gonna be so tight to call.

K

am afraid those sorts of gains are just cumulative, they interact with each other, therefor a 3 x 3% gains (in isolation) might be 5% overall gain. but a gains a gain.

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I wonder if the "chants remark" about 3.5x twspd is desined more to cast a tyny shaddo over J Spittles holiday than to enlihgten us.

 

Personelly I think ill wate til it happens to get all ecxitered about it....

When they cracked 41 knots today, i suspect it was riding the increasing wind. maybe 16-17 knots. But still good speed.

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ps, amazes me that the upwind speed doesn't really increase much more from about 13-18knots, the were still doing good upwind speeds today. short of upwind foiling it seems there is a "limiting factor" that restricts gains. i suspect that the real aero limitations dont kick in till over 50knots downwind.

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Remember what Vesta's Sailrocket found: traditional foils have a massive massive drag barrier at just below 50 knots. So I don't think its is aero effects that are limiting top speeds off wind.

 

Upwind sure. Because if you are doing 18 knots upwind in 17 knots of breeze at a TWA of about 30 deg, you are seeing something like 30-35knots AWS against your CMG. Offwind at the 150 deg they are sailing towards the finish, That's about the same (I'm ballparking here, someone else can run the actual numbers) So I would suggest that upwind its aerodrag that is lmiting them out at 18 knots and off the wind it is foil drag

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

OK sneaks, u may be right. Please be reminded how important the go fast bolt on bits are for ETNZ in their champagne.

But.... wot iff someone was somehow to reduce drag on their boat by more than 3%. And conversely they also managed to wring another 4% out of a revamped wing, plus say 4% improvement in foil drag/lift, plus a 10% increase in AC wind limit over the LV limit= ay around 15% overall speed diff improvmnts.

All hipotheatrical i know but I think thats wot the ETNZ chief engineer Giovanni Belgrano was referring to maybe? its a kiwi trait , but its great to get an honest answer aint itt? ....or maybe its an Italian trate?

Cheers till Sept 7. Go the kiwi guys in the youth worlds...its gonna be so tight to call.

K

am afraid those sorts of gains are just cumulative, they interact with each other, therefor a 3 x 3% gains (in isolation) might be 5% overall gain. but a gains a gain.

Thanks Qman, u r right of course. But what if several gains were made simutaneously? Could be a winner. GB would know eh?

Conversely some gains do compound as with wing plus lower drag,plus faster foil. I think that there is greater opportunity to achieve biggest gains in the lower wind range as we saw today.

 

 

Cheers

K

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hmm ... going from 3 to 3.5x wspd is over 16% increase,

 

eg from 45 knots to over 52 knots.

 

sounds .... ambishis

 

maybe he menes at low windspds (which cd be a wurry for OR)

OK sneaks, u may be right. Please be reminded how important the go fast bolt on bits are for ETNZ in their champagne.

But.... wot iff someone was somehow to reduce drag on their boat by more than 3%. And conversely they also managed to wring another 4% out of a revamped wing, plus say 4% improvement in foil drag/lift, plus a 10% increase in AC wind limit over the LV limit= ay around 15% overall speed diff improvmnts.

All hipotheatrical i know but I think thats wot the ETNZ chief engineer Giovanni Belgrano was referring to maybe? its a kiwi trait , but its great to get an honest answer aint itt? ....or maybe its an Italian trate?

Cheers till Sept 7. Go the kiwi guys in the youth worlds...its gonna be so tight to call.

K

am afraid those sorts of gains are just cumulative, they interact with each other, therefor a 3 x 3% gains (in isolation) might be 5% overall gain. but a gains a gain.

Thanks Qman, u r right of course. But what if several gains were made simutaneously? Could be a winner. GB would know eh?

Conversely some gains do compound as with wing plus lower drag,plus faster foil. I think that there is greater opportunity to achieve biggest gains in the lower wind range as we saw today.

 

 

Cheers

K

Apparent wind sailing is a funny beast, the faster you go the faster you can got the faster you can go.

 

Just imagine the posibility if they were 1. allowed control surfaces, 2. allowed to add to the righting moment with the windward foil.

 

The gains would be phenomenal. As would the forces.

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What has not been explained here and has been discussed with other guru,s is the fact that...

 

These boats only foil at the current upper wind limit, which is to low!!.

 

Below this wind limit they they have struggled to foil consistantly for longer than 20sec, and would not even look at foiling, even without course borders, because the VMG to the top mark is slower that sailing off the foil and on a higher course.

 

After all if you were in one side of the course and wanted to hit the other side why would you not foil if it was faster?(as we have seen on a few occasions)... why? Because they can't and its not producing a better VMG to the Top Mark.

 

Because they

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^ My guess would be that there would be a difference in size and shape of the optimal foils to foil upwind and downwind, as you need to lift off at a lower speed upwind.

As the course they sail is basically 1/3 upwind an 2/3 downwind, they tend use foils that are tilted performance wise for high-speed downwind sailing. I also believe that G. Belgrano is into an important point with the short and narrow course you want to chose the high-pointing mode in order to reduce the number of tacks compared to a low-pointing foiling mode upwind.

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^ My guess would be that there would be a difference in size and shape of the optimal foils to foil upwind and downwind, as you need to lift off at a lower speed upwind.

As the course they sail is basically 1/3 upwind an 2/3 downwind, they tend use foils that are tilted performance wise for high-speed downwind sailing. I also believe that G. Belgrano is into an important point with the short and narrow course you want to chose the high-pointing mode in order to reduce the number of tacks compared to a low-pointing foiling mode upwind.

What if they can stay on the foils through the tack?

 

I've been totally blown away by the speed these cats actually do a displacement tack.

Far, far better than I would ever have believed possible.

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^ My guess would be that there would be a difference in size and shape of the optimal foils to foil upwind and downwind, as you need to lift off at a lower speed upwind.

As the course they sail is basically 1/3 upwind an 2/3 downwind, they tend use foils that are tilted performance wise for high-speed downwind sailing. I also believe that G. Belgrano is into an important point with the short and narrow course you want to chose the high-pointing mode in order to reduce the number of tacks compared to a low-pointing foiling mode upwind.

Which if you add in the multiplier for the extra distances sailed in tacking upwind comes closer to 50/50 - yes they are "tacking downwind" but at deeper angles than upwind (ie Upwind they are tracking about 60deg betweeen tacks and off the wind its closer to 30 deg.

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^^ The faster you can tack the better of course, but what I have seen so far only shows that they start tacking whilst foiling, and not that they continue foiling on the other tack. But foiling into the tack would increase the speed through the tack, as it is less time that the 72' long hulls needs to be swung round.

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I have created this spreadsheet that calcs the actual VMG from speed and pointing angle. Please have a look and pull it apart as necessary. This is the first file I have shared using Google Docs so I hope it is visible.What it does show there is a cross over in pointing and speed where it is not an option.

 

https://docs.google.com/file/d/0B5Oo63XcEYuOeExVaGR2RlBGeWs/edit?usp=sharing

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As pointed out in the other thread there are ways to design the foils to eliminate the biggest cause of upwind leeway-the "V". First Team to do it will win (if they keep it secret until September). I'll bet foiling upwind w/o excessive leeway is topic #1 in R&D these days.

 

What's the "V"?

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Foiling upwind? ... Sure, if the foil depth can be controlled well enough to get net gains between leeway and speed.

 

When half the foil is carving air, the bottom half has to support all of the lateral forces. Ride higher than that, and a third of the board has to support 3x its full-depth loading. So it's a fair bet that flying could reduce drag but also loses some leeway

 

NZ have already said they tweak the leeward board pitch angle upwind, just enought lift the hull to skimming.

Maybe they'veth looked into that, run VMG trials, found the fasr settings, ride-heights, etc.

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Is it going to be called a,

 

Fack

Flack

 

or

?

When they do it several times to proof it is intentional and it is obvious that it is way faster than tacking?

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⬆ gold

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...

 

BTW did you see OR latest near wipout on video , same as ETNZ, but saved by the jib release. Lucky. Whew!

....

 

No. Link pleez?

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...

 

BTW did you see OR latest near wipout on video , same as ETNZ, but saved by the jib release. Lucky. Whew!

....

 

No. Link pleez?

Would be interested in seeing this also.

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