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29 minutes ago, hoom said:

Is that 'have to' or 'able to'?

LR has been super slow out of quite a lot of tacks.

I think they have to due to smaller foils but it certainly ain't hurting them.

Interesting that they sailed shorter distance as well as faster speed I race 6 today.

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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

8 hours ago, erdb said:

But this is all viscous drag, not induced, right? Induced drag is far greater. Unfortunately, we don't have simple tools to analyze a complex scenario like an asymmetrically loaded Y foil.

...

 

Take a look at AVL.  Like Xfoil, it was written by Prof. Mark Drela of MIT and Hal Youngren.  It is capable of analyzing the lift and induced drag of a Y foil, with the infinite Froude number approximation for the free surface.  

What I like to do is to set up a spreadsheet to create the input files for AVL.  I read in sample .AVL, .RUN, and .MASS files as space delimited text files and put them in separate sheets.  Then I create a geometry sheet that has the manual inputs and calculations for all the parameters.  The other sheets are then modified to suit the geometry and the numbers replaced by cell formulas that link back to the geometry sheet.  To make a run, I save each of the sheets as a tab delimited text file, then edit those to replace the tabs with spaces.  That gives me the input files for an AVL run.  

The geometry sheet is easier to read than the AVL input files.  It also makes it easy to handle the different immersion of the strut due to flying height or boat attitude changes.  The strut, of course, needs to be clipped at the water surface, and that can be done by calculations in the geometry sheet.  

I've used AVL for inverted T and inverted pi (two struts) foils, plus section data from Xfoil and empirical spray drag, and been able to to come within 10% of the total drag from RANS CFD of the same configuration and operating conditions.  

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3 hours ago, Basiliscus said:

Take a look at AVL.  Like Xfoil, it was written by Prof. Mark Drela of MIT and Hal Youngren.  It is capable of analyzing the lift and induced drag of a Y foil, with the infinite Froude number approximation for the free surface.  

What I like to do is to set up a spreadsheet to create the input files for AVL.  I read in sample .AVL, .RUN, and .MASS files as space delimited text files and put them in separate sheets.  Then I create a geometry sheet that has the manual inputs and calculations for all the parameters.  The other sheets are then modified to suit the geometry and the numbers replaced by cell formulas that link back to the geometry sheet.  To make a run, I save each of the sheets as a tab delimited text file, then edit those to replace the tabs with spaces.  That gives me the input files for an AVL run.  

The geometry sheet is easier to read than the AVL input files.  It also makes it easy to handle the different immersion of the strut due to flying height or boat attitude changes.  The strut, of course, needs to be clipped at the water surface, and that can be done by calculations in the geometry sheet.  

I've used AVL for inverted T and inverted pi (two struts) foils, plus section data from Xfoil and empirical spray drag, and been able to to come within 10% of the total drag from RANS CFD of the same configuration and operating conditions.  

Basiliscus have you looked at open vsp and vsaero?

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4 hours ago, Basiliscus said:

Take a look at AVL.  Like Xfoil, it was written by Prof. Mark Drela of MIT and Hal Youngren.  It is capable of analyzing the lift and induced drag of a Y foil, with the infinite Froude number approximation for the free surface.  

What I like to do is to set up a spreadsheet to create the input files for AVL.  I read in sample .AVL, .RUN, and .MASS files as space delimited text files and put them in separate sheets.  Then I create a geometry sheet that has the manual inputs and calculations for all the parameters.  The other sheets are then modified to suit the geometry and the numbers replaced by cell formulas that link back to the geometry sheet.  To make a run, I save each of the sheets as a tab delimited text file, then edit those to replace the tabs with spaces.  That gives me the input files for an AVL run.  

The geometry sheet is easier to read than the AVL input files.  It also makes it easy to handle the different immersion of the strut due to flying height or boat attitude changes.  The strut, of course, needs to be clipped at the water surface, and that can be done by calculations in the geometry sheet.  

I've used AVL for inverted T and inverted pi (two struts) foils, plus section data from Xfoil and empirical spray drag, and been able to to come within 10% of the total drag from RANS CFD of the same configuration and operating conditions.  

Is there much difference from calculating the wings and strut/arm separately via the equation Di = L^2 / (pi * e * qbar * b^2)  ?

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5 hours ago, gigi said:

Basiliscus have you looked at open vsp and vsaero?

A little bit, but haven't tried to use them, yet.

I also use the CMARC panel code, and have written a Rhino plug-in to generate PMARC formatted input files.

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5 hours ago, MaxHugen said:

Is there much difference from calculating the wings and strut/arm separately via the equation Di = L^2 / (pi * e * qbar * b^2)  ?

I don't think you can calculate the induced drag separately because the three surfaces are tightly coupled, and the strut may not be loaded very much to begin with.  

The key in that equation is the Oswald efficiency factor, e.  You can also group the efficiency with the span to form an effective span, as in b_eff = sqrt(e)*b.  The effective span is perhaps a more intuitive way of looking at it.  But either way, you need to use at least a lifting line method to get the effective span (or e).  Stepping up in order of sophistication from lifting line would be vortex lattice (like AVL), panel code, and CFD.  

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I’ve noticed that LR & NZ the mainsail double membrane leeches are different -

LR, the leeches meet, and the flow, at least indicated by the leech telltale, which flows more like a single membrane sail leech telltale would.

NZ, the leaches are separated by what 5-6 inches, and the telltale in front of the camera actually gets sucked directly and tightly into that space-

Would this make for different flow (sheet vortices in the Trrrffetz plane or a Von Karman vortex street for all I know) for NZ off their leeches down wind?  Differences in induced drag?  The opposite might be a jet of faster air coming out of that space.....:rolleyes:

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6 minutes ago, Amati said:

I’ve noticed that LR & NZ the mainsail double membrane leeches are different -

LR, the leeches meet, and the flow, at least indicated by the leech telltale, which flows more like a single membrane sail leech telltale would.

NZ, the leaches are separated by what 5-6 inches, and the telltale in front of the camera actually gets sucked directly and tightly into that space-

Would this make for different flow (sheet vortices in the Trrrffetz plane or a Von Karman vortex street for all I know) for NZ off their leeches down wind?  Differences in induced drag?  The opposite might be a jet of faster air coming out of that space.....:rolleyes:

That's interesting! Perhaps that's one reason why TR gains more when ahead? Perhaps that's one reason LR had wind issues in the start box?

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Ok, so it turns out that truncating the trailing edge of certain sections can increase max lift coefficients (as well as screw with drag, so ....). Maybe the crappyness of the double membrane wing demands it, or NZ needed some extra lift to get their tiny foils some extra grunt in the light stuff?  (And less drag of the foils made up for increased sail drag, and was more use with more sail lift?)  And maybe (?) given the Bat Wing adventure, maybe this (which ventures into some of this) will be helpful.  You do have to buy into acoustic aspects of wing design, though....:)....

https://www.imperial.ac.uk/media/imperial-college/research-centres-and-groups/turbulence-mixing-and-flow-control-group/AIAA_FracWing.pdf

 

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Abrupt stall is an issue with blunt truncated trailing edge, but it looks like NZ is adjusting their main aoa a lot more, so maybe this is what’s going on-  more ticklish higher performance than LR going with a more forgiving package in general.  Would explain why NZ is so good when ahead, and not so good behind, and why LR kills in maneuver, lower, and bumpier wind speed?  Except for yesterday, falling in that hole at the start.

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6 hours ago, Amati said:

I’ve noticed that LR & NZ the mainsail double membrane leeches are different -

LR, the leeches meet, and the flow, at least indicated by the leech telltale, which flows more like a single membrane sail leech telltale would.

NZ, the leaches are separated by what 5-6 inches, and the telltale in front of the camera actually gets sucked directly and tightly into that space-

Would this make for different flow (sheet vortices in the Trrrffetz plane or a Von Karman vortex street for all I know) for NZ off their leeches down wind?  Differences in induced drag?  The opposite might be a jet of faster air coming out of that space.....:rolleyes:

I think that they are using the Kammback effect in light winds. In some clear stern shots I've noticed that the gap gets progressively narrower up the sail leech.

They don't use "the gap" in moderate winds or higher, apart from the first metre or two which is unavoidable due to the rams at the clew area.

I've tested my mainsail profile in XFoil, and using the gap does increase the CL of the sail, although the L/D ratio is slightly lower.

image.png.70c76152c2f67fb044d35993ccb01f08.png

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8 minutes ago, MaxHugen said:

I think that they are using the Kammback effect in light winds. In some clear stern shots I've noticed that the gap gets progressively narrower up the sail leech.

They don't use "the gap" in moderate winds or higher, apart from the first metre or two which is unavoidable due to the rams at the clew area.

I've tested my mainsail profile in XFoil, and using the gap does increase the CL of the sail, although the L/D ratio is slightly lower.

image.png.70c76152c2f67fb044d35993ccb01f08.png

 

8 minutes ago, MaxHugen said:

I think that they are using the Kammback effect in light winds. In some clear stern shots I've noticed that the gap gets progressively narrower up the sail leech.

They don't use "the gap" in moderate winds or higher, apart from the first metre or two which is unavoidable due to the rams at the clew area.

I've tested my mainsail profile in XFoil, and using the gap does increase the CL of the sail, although the L/D ratio is slightly lower.

image.png.70c76152c2f67fb044d35993ccb01f08.png

Does the gap getting smaller match platform taper?  Or the effective l/d (don’t know what else to call it) distribution? 

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5 minutes ago, Amati said:

 

Does the gap getting smaller match platform taper?  Or the effective l/d (don’t know what else to call it) distribution? 

I haven't checked that, it was just an observation.

But knowing the "Krafty Kiwis" they probably worked the gap out to match the spanwise Lift distribution?  :D

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29 minutes ago, nav said:

^ PB just said they are working to reduce the gap to get closer to LR's set up:)

Yes, Xerox, and you don't think the Italians are working one step ahead in the while ?

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Glad we didn't have racing today, hopefully it pushes out the schedule to get into some windier days. I'd really love to see what TR can do in the upper range.

While we were waiting, I've analyzed data from yesterday, and the good news is that it seems the wind direction calibration on ETNZ has been fixed or at least improved! If it was done by someone reading these posts - thanks!!!

First the VMGs, just to check overall performance - marginal advantage to ETNZ, but it's there.

Race 1:

289219280_uwvmg.png.3bee9ba591a6e50a0d5a22fdb1ff55b0.png160291772_dwvmg.png.33d4761b7d74e2e801722e6c6c55247c.png

Race 2:

2040214151_uwvmg.png.9f7923eed5da144c28106695d0a70418.png1694781928_dwvmg.png.0bb5cf0f9e7008be7d11eeeaba20998c.png

Some interesting differences in how ETNZ's heel and cant angles changed relative to the first day - I assume because of the lighter air.

On the first day, race 2 was sailed in 14+ kts of wind. Upwind, ETNZ sailed with a slight leeward heel on average, while LR had a slight windward heel. Foil cant angle, as we discussed, was in general much higher for ETNZ with a wide range of angles used. Effective cant angle (heel+cant), was closer between the two boats, but ETNZ's was still higher:

2025143464_uwheel.png.0f19219877546fa5e550bbf89a046bf9.png657881754_uwcant.png.ee4a19b14663624ec685e936973f646f.png

 

1618831456_uweffcant.png.1fabec90d3acfdc56a1b36ae5150565e.png

Interestingly, in lighter winds (8-9kts), like in race 5, ETNZ sails with quite a bit of windward heel whereas LR has about the same heel as in stronger wind. I always thought they'd heel more to windward as the wind gets stronger to use the extra righting moment given by the weight of the rig. Foil cant angles again varied widely for ETNZ, but surprisingly, now they had a lower cant angle than LR on average: 

1640835641_uwheel.png.a0ffa459e2a5871dd06ba650a0b333a1.png1664172123_uwcant.png.26fb958fa7f523258fd5871f08a5b496.png

Looking at the effective cant angle, it's obvious why - they need to compensate for the windward heel to produce an overall effective cant angle similar to LR's:

493843940_uwefcant.png.6cdedbaf17cd580092b73b787c44318c.png

Downwind, things change less with windspeed, but ETNZ does heel more to windward in the light air while LR has about the same heel regardless of wind strength.

Any guesses why ETNZ would heel more to windward in light wind?

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ETNZ still does the rolling tack with a big change in heel before and after tack. It seems LR is trying to do something, too, but the timing is a bit different, they heel to lee momentarily after the tack and the range of heel angles is lower (negative is windward, vertical line is time of tack):

105538775_theel.png.6524141ca6b9b0def92e8f30b083c9cb.png

Interestingly, LR actually lost more distance in the tacks than ETNZ having a slower recovery of VMG after the tack (this is race 6):

1820884185_tvmg.png.837f08257b99dfe75780c14f3c33b9e6.png1967834058_tvmgs.png.0f5ec402485ebe96c48afcc907a26752.png

Although their speed came back faster, they had to point lower coming out of the tack. Kind of the opposite what I expected with large foil vs small foil. 

2035408209_tbs.png.64e425a8031ba1f28a9ebcd419f8856a.png1861394299_ttwa.png.b53169ff3a8adf8eaed8fe4505551e27.png

Jibe angles were very similar, but ETNZ was faster overall:

147770531_jvmg.png.fca139044ba2ac721d0fd40604148676.png313476596_jbs.png.1ab73b58dc449c64ebfea9d1884e624c.png

2012617521_jtwa.png.41ca755c2bd75fcfbd69e067666c3cb9.png

 

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53 minutes ago, The Advocate said:

I just came across this and don't resall seeing it posted. Interesting from a visual sense.

 

Yes, I posted this some time ago, great example of leading edge cavitation isn't it.

The foil appears to have quite a flat upper profile, so that the pressure remains fairly constant over the chord, so not surprising cavitation starts at the LE, rather than mid-chord.

If the AoA marked is accurate at just ~1°, the water velocity must have been up there!

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7 minutes ago, MaxHugen said:

Yes, I posted this some time ago, great example of leading edge cavitation isn't it.

The foil appears to have quite a flat upper profile, so that the pressure remains fairly constant over the chord, so not surprising cavitation starts at the LE, rather than mid-chord.

If the AoA marked is accurate at just ~1°, the water velocity must have been up there!

Bugger, no worries. Sorry about that.

Yes it is, I would suggest that is a high speed foil. I found a paper on 120 knot foils a while back but don't think I posted it. Will look for it if you think it is of interest.

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1 minute ago, The Advocate said:

Bugger, no worries. Sorry about that.

Yes it is, I would suggest that is a high speed foil. I found a paper on 120 knot foils a while back but don't think I posted it. Will look for it if you think it is of interest.

No worries. And thanks, I've read the paper, it was a study for a high speed littoral boat for the Navy by Prof Brizzolara. Interesting, especially the extra section they added to the flat TE to improve low speed performance.
Brizzolara - Dual-Mode Super-Cavitating Hydrofoils.pdf

I tried to recreate that foil profile and try it out in XFoil, but I have probs without an app to design such complex foils.

Got a profile somewhat along those lines, but couldn't get XF to resolve it at most AoAs. :(

image.thumb.png.cf4d0b86f7c99c79b2978fd9a0ba5b53.png

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8 minutes ago, MaxHugen said:

No worries. And thanks, I've read the paper, it was a study for a high speed littoral boat for the Navy by Prof Brizzolara. Interesting, especially the extra section they added to the flat TE to improve low speed performance.
Brizzolara - Dual-Mode Super-Cavitating Hydrofoils.pdf

I tried to recreate that foil profile and try it out in XFoil, but I have probs without an app to design such complex foils.

Got a profile somewhat along those lines, but couldn't get XF to resolve it at most AoAs. :(

image.thumb.png.cf4d0b86f7c99c79b2978fd9a0ba5b53.png

Yes, that's the one!

Very interesting paper. I wonder how long it will be before the brains trusts can hit those numbers under sail!

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1 minute ago, The Advocate said:

Yes, that's the one!

Very interesting paper. I wonder how long it will be before the brains trusts can hit those numbers under sail!

I'd be willing to bet a few bucks that a way to transition from sub to super cavitating foils will be worked out by AC37 by some smart cookie. :)

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2 hours ago, erdb said:

Glad we didn't have racing today, hopefully it pushes out the schedule to get into some windier days. I'd really love to see what TR can do in the upper range.

While we were waiting, I've analyzed data from yesterday, and the good news is that it seems the wind direction calibration on ETNZ has been fixed or at least improved! If it was done by someone reading these posts - thanks!!!

First the VMGs, just to check overall performance - marginal advantage to ETNZ, but it's there.

Race 1:

289219280_uwvmg.png.3bee9ba591a6e50a0d5a22fdb1ff55b0.png160291772_dwvmg.png.33d4761b7d74e2e801722e6c6c55247c.png

Race 2:

2040214151_uwvmg.png.9f7923eed5da144c28106695d0a70418.png1694781928_dwvmg.png.0bb5cf0f9e7008be7d11eeeaba20998c.png

Some interesting differences in how ETNZ's heel and cant angles changed relative to the first day - I assume because of the lighter air.

On the first day, race 2 was sailed in 14+ kts of wind. Upwind, ETNZ sailed with a slight leeward heel on average, while LR had a slight windward heel. Foil cant angle, as we discussed, was in general much higher for ETNZ with a wide range of angles used. Effective cant angle (heel+cant), was closer between the two boats, but ETNZ's was still higher:

2025143464_uwheel.png.0f19219877546fa5e550bbf89a046bf9.png657881754_uwcant.png.ee4a19b14663624ec685e936973f646f.png

 

1618831456_uweffcant.png.1fabec90d3acfdc56a1b36ae5150565e.png

Interestingly, in lighter winds (8-9kts), like in race 5, ETNZ sails with quite a bit of windward heel whereas LR has about the same heel as in stronger wind. I always thought they'd heel more to windward as the wind gets stronger to use the extra righting moment given by the weight of the rig. Foil cant angles again varied widely for ETNZ, but surprisingly, now they had a lower cant angle than LR on average: 

1640835641_uwheel.png.a0ffa459e2a5871dd06ba650a0b333a1.png1664172123_uwcant.png.26fb958fa7f523258fd5871f08a5b496.png

Looking at the effective cant angle, it's obvious why - they need to compensate for the windward heel to produce an overall effective cant angle similar to LR's:

493843940_uwefcant.png.6cdedbaf17cd580092b73b787c44318c.png

Downwind, things change less with windspeed, but ETNZ does heel more to windward in the light air while LR has about the same heel regardless of wind strength.

Any guesses why ETNZ would heel more to windward in light wind?

Interesting. Was very visible watching.

Windward heel may increase RM from a CoG perspective, but the sail will also start to produce some vertical lift component. Depends how heavy the mast, sail and rigging is to weather you end up with more RM or less. 

Windward heel but less cant will give the same foil cant angle relative to the water (relative cant angle) but it would also give you the same ride height, but with same foil depth despite the heel. But the cant would still reduce the lever? All this may be about reducing RM without running the foil deeper or the hull higher. 

It could also be about helm balance. If they are slightly under canvassed and trimming the main on hard with no more jib available it will move the CoE back and produce weather helm which can be compensated for with windward heel. 

 

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35 minutes ago, MaxHugen said:

I'd be willing to bet a few bucks that a way to transition from sub to super cavitating foils will be worked out by AC37 by some smart cookie. :)

I tend to agree with you. The only issue I see is overcoming sail plan drag.

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2 minutes ago, The Advocate said:

I tend to agree with you. The only issue I see is overcoming sail plan drag.

May well become an issue, but we do see ice and land yachts reaching much higher speeds. Foils currently make up 50% plus of drag, and that's not likely to improve with super cavitating ones I think.

So a "conventional" sail plan to generate enough power to overcome that foil drag might become difficult?

@Basiliscus has experience with land yachts (I think), may have some views on sail power vs this level of drag.

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Btw can someone give me a link to the rules, where it is stated about the amount of foils that the teams were able to produce and what can be used in the ac final

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7 hours ago, The Advocate said:

I tend to agree with you. The only issue I see is overcoming sail plan drag.

Getting rid of jibs might help.....

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8 hours ago, MaxHugen said:

May well become an issue, but we do see ice and land yachts reaching much higher speeds. Foils currently make up 50% plus of drag, and that's not likely to improve with super cavitating ones I think.

So a "conventional" sail plan to generate enough power to overcome that foil drag might become difficult?

@Basiliscus has experience with land yachts (I think), may have some views on sail power vs this level of drag.

I don't see supercavitating foils being used for America's Cup yachts - the drag is too high.  They are especially bad at subcavitating speeds. 

Instead, I think some teams may already be using transcavitating foils.  These are shaped a lot like subcavitating foils, but are designed to still work well when cavitating over part of the surface.  It would require a multi-phase RANS CFD code to analyze the performance of transcavitating foils.

When I was landsailing, the best of the rigid wing rigs and the best of the wingmast-sail combinations were about equal.  Rigid wing rigs without flaps were not competitive.  Their top end speed was OK, but they took too long to accelerate to speed.  

I'm actually surprised that AC sailors don't go landsailing.  When BMW Oracle was in San Diego, I tried to convince some of them to go up to the Antelope Valley to go landsailing with my friends in the Wind Wizards club on El Mirage.  Even a simple open frame landyacht sails at the same speeds and apparent wind angles as the AC75s and F50s are now hitting.  Landyachts are also hard to get going in light winds due to friction, so they would be a good way to get an intuitive feel for apparent wind sailing.  You could put a grinder in a landyacht and he'd quickly learn what's going on, without having to build a lot of sailing skills. 

Today, of course, sailors use the Moth for foiling practice.  But the Moth requires a lot of skill just to be able to sail in the first place.  Landyachts are very easy to sail.  They're like fighter planes - they go where you point them.  And being close to the ground gives you a great sense of speed.  The most fun you can have lying down with your clothes on.

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6 minutes ago, Erwankerauzen said:

Does it mean symetric wing section ?

No camber adjustments?

Yes.

Interestingly, Iron Duck, which Bob Dill used to set a world landsailing speed record, was of this type. as is (based on the pictures I've seen) Greenbird, Richard Jenkins' current speed record holder.  Prior to that, the record was held by a Nord Design Friendship, which has a wingmast-sail rig, but when the winds were too high to race they went out sailing with mast alone.  So it was a symmetrical wingsail, too!

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2 hours ago, Basiliscus said:

I don't see supercavitating foils being used for America's Cup yachts - the drag is too high.  They are especially bad at subcavitating speeds. 

Instead, I think some teams may already be using transcavitating foils.  These are shaped a lot like subcavitating foils, but are designed to still work well when cavitating over part of the surface.  It would require a multi-phase RANS CFD code to analyze the performance of transcavitating foils.

When I was landsailing, the best of the rigid wing rigs and the best of the wingmast-sail combinations were about equal.  Rigid wing rigs without flaps were not competitive.  Their top end speed was OK, but they took too long to accelerate to speed.  

I'm actually surprised that AC sailors don't go landsailing.  When BMW Oracle was in San Diego, I tried to convince some of them to go up to the Antelope Valley to go landsailing with my friends in the Wind Wizards club on El Mirage.  Even a simple open frame landyacht sails at the same speeds and apparent wind angles as the AC75s and F50s are now hitting.  Landyachts are also hard to get going in light winds due to friction, so they would be a good way to get an intuitive feel for apparent wind sailing.  You could put a grinder in a landyacht and he'd quickly learn what's going on, without having to build a lot of sailing skills. 

Today, of course, sailors use the Moth for foiling practice.  But the Moth requires a lot of skill just to be able to sail in the first place.  Landyachts are very easy to sail.  They're like fighter planes - they go where you point them.  And being close to the ground gives you a great sense of speed.  The most fun you can have lying down with your clothes on.

These are all you'd need, plenty about, I'm sure some will have been out for a blast...

Blobart-BK-2014-32.jpg

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1 hour ago, dorox said:

All data files are here: https://github.com/dorox/ac36_data

Brilliant! I hope to have fun with this, in the coming months. 
 

Is this a Linux command? 


—-

For convenience, it can be installed with 

pip install git+https://github.com/dorox/ac36_data:

this will install the ac36data package containing 1Hz data with convenience data access functions.

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12 minutes ago, Stingray~ said:

Brilliant! I hope to have fun with this, in the coming months. 
 

Is this a Linux command? 


—-

For convenience, it can be installed with 

pip install git+https://github.com/dorox/ac36_data:

this will install the ac36data package containing 1Hz data with convenience data access functions.

That's to install Python package. It requires python installed on your PC, and works with any OS. Once installed, access the boats telemetry data with Python command:
"data = ac36data.get_boats('ac2021',1)"
where 'ac2021' - event name, "1" - race number.

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supercavitating foils will only ever be useful at >20-30kt wind speeds, and never if there isn't a lot of time spent reaching. Those winds speeds are very infrequent almost everywhere in the world, and generally come with big waves too that destroy their utility on sailing yachts.  Their profile lift to drag maxes out in low teens, where conventional foils can exceed 100.  As a practical thing you would need to switch between supercavitating and conventional foils at lower speeds to make them useful for sailing.

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4 minutes ago, dorox said:

That's to install Python package. It requires python installed on your PC, and works with any OS. Once installed, access the boats telemetry data with Python command:
"data = ac36data.get_boats('ac2021',1)"
where 'ac2021' - event name, "1" - race number.

Thanks, very cool.

Should the data be easily importable into database tables? 

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23 minutes ago, Foyle said:

supercavitating foils will only ever be useful at >20-30kt wind speeds, and never if there isn't a lot of time spent reaching. Those winds speeds are very infrequent almost everywhere in the world, and generally come with big waves too that destroy their utility on sailing yachts.  Their profile lift to drag maxes out in low teens, where conventional foils can exceed 100.  As a practical thing you would need to switch between supercavitating and conventional foils at lower speeds to make them useful for sailing.

IKR, just like a handful of years back when they said 70 ft yachts would foil one day, dreamers.

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14 minutes ago, Stingray~ said:

Thanks, very cool.

Should the data be easily importable into database tables? 

If you know python then yes, otherwise I'll convert the data into .csv files once the whole event is over.

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TR has smaller foils than LR so can go faster but makes a longer course.

With light wind conditions LR should be favoured however both boats are equal, so can TR be faster in stronger winds ? perhaps, but in stronger winds LR can point higher and go deeper so it is a tough answer. Let's say that TR would be favoured downwind and LR could do as well or better upwind and during manoeuvers.

So what strategy for LR ? The best for them would be to use their manoeuvrability to make the kiwi fall of their foils in the prestart or even bring them to a capsize, that would not please to some but could be interesting.

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3 hours ago, nav said:

These are all you'd need, plenty about, I'm sure some will have been out for a blast...

Blobart-BK-2014-32.jpg

Blokarts may be numerous, but a better choice would be an International 5.5 Square Meter or a Standart class.    

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2 hours ago, dorox said:

If you know python then yes, otherwise I'll convert the data into .csv files once the whole event is over.

Please do? You are f’ing awesome, am on my knees in admiration. 

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Pure gold, Guillaume Verdier himself give very simple answers with a lot of common sense for a lot of questions debated here, by the two Italians, Mozzy. You have to understand French though.

I'll come back with some points when I have time, unless somebody does it before.

https://voilesetvoiliers.ouest-france.fr/regate/coupe-de-l-america/america-s-cup-guillaume-verdier-du-vendee-globe-a-la-coupe-de-l-america-sur-tous-les-fronts-16505d9a-7daf-11eb-a530-8257a05e6295?fbclid=IwAR1NxsAj3wAuWdzn6_P7iVTxshZyq76ZeZcZfnogKPj0O9F0JBzZQrROne8

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3 hours ago, Tornado-Cat said:

Pure gold, Guillaume Verdier himself give very simple answers with a lot of common sense for a lot of questions debated here, by the two Italians, Mozzy. You have to understand French though.

I'll come back with some points when I have time, unless somebody does it before.

https://voilesetvoiliers.ouest-france.fr/regate/coupe-de-l-america/america-s-cup-guillaume-verdier-du-vendee-globe-a-la-coupe-de-l-america-sur-tous-les-fronts-16505d9a-7daf-11eb-a530-8257a05e6295?fbclid=IwAR1NxsAj3wAuWdzn6_P7iVTxshZyq76ZeZcZfnogKPj0O9F0JBzZQrROne8

TNZ

-          My first meeting with TNZ was in 2009

-          I begain to work in 2010

-          I have aneye on everyting on the boat but works part time because busy on other projects

-          I give ideas but it’s a lot of work, you have to develop it each idea

-          I like a small team because it’s efficient, we are even too many, lots of people coding, too many, we have to keep a global vision

AC75

-          One day day Ray Davis asks me to meet Howard Spencer, willing to get a fun 40 ft.

-          I design a foiling mono

-          Ray says that the keel is too much

-          I tell him it’s possible, however we need stability

-          I remember that a french architect, Martin Defline has made two queels boats who are pretty efficient, so we can do the same thing with ballast at the end of the foil

-          It’s counter intuitive to put weight where we want a lift but calcules show it is 50% more efficient that with the keel for the same mass.

-          The project doesn’t work as too expensive

-          The Italians want a big mono for AC36, we could have a had a smaller boat for economic reasons

-          Ray Davies puts my drawing on the table, everybody laugh. He tells us: I give you one month to test the concept to test If it works in a simulator. I was not there, I did not test, Bobby tested the design and they said it was a fun concept and it works

-          They tried other concepts but came back to the initial one

 

 

AC75 rule

-          I was willing two rudder foils for better stability to avoid diagonal heel instability like the hydrotère.

-          I was against it but we went to one rudder for a good reason: to avoid cutting a crew falling in the water. That is also why the rules prevent going on the bow.

-          I did not write the rule, Dan Bernasconi did it, I gave my advices.

-          We chose a close rule to avoid mistakes, it took us a year

-          We were very reassured to see that the british model worked, simulation works but is not always reassuring.

-          We surely took some advance compared to the other teams but I don’t think it was so much

-          Once I chose a concept I like to push it to the end.

-          We got symetric foils at the end only in order to learn as much as possible

-          The bulb at the end of the foil arm is just to put ballast, it has nothing to do with hydro but with the rule

 

Our AC75

-          We are given a rule that I hate, the inertial stability in the harbour that imposes a wide flotation beam

-          I understand it but it was not required with the ballasted foils in the water, we did not need that. 10’17

-          I understood that it was obvious that we have to make a central tube like a trimaran hull and a wide ass for the rule and stability, I don’t think other teams understood it right away: narrow hull and wide as far on the back as possible.

-          So we have a narrow hull in the front like a trimaran and a wide ass for static stability in the harbour.

-          Not a big evolution between B1 and B2, B2 is even more like a multi

-          We want a boat easy to foil that lift the stern first and get early on the foils for lower drag asap

-          The brits were capsizing when bearing away as they could not get enough lift from the foil vs the pressure. They were afraid of the transition and they were right to have a first boat with more stability.

-          B1 was an hydro dynamic concept, B2 an aero + hydro

The foil

-          The dihedral is more equlibrated and does not require a big “shaft” that maintain the foil and which creates drag

-          On the other hand a flat design is simpler and has lower drag. Both concepts are good.

B  

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Race 9 is uploaded. I've included course-VMG to see how each team handles the wind.

The screenshot shows the 6kn CVMG advantage for NZL at the 5th leg when they got the lead.

image.thumb.png.05fc69f3f5bc646ad11511b706b15250.png

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As we are getting closer to the end, I ran the "summarize all races" algorithm again to see how the boats ranked and how much improvement was made by LR and ETNZ.

LR's and ETNZ's AC races are marked by triangles and darker red and green trend lines vs their previous ACWS and Prada cup races.

VMG vs TWS:vmg.thumb.png.5ef63b849209e48b59a4d5cede1be2a6.png

Altogether, ETNZ were always superior both upwind and downwind. They did improve since the ACWS, but LR actually improved a lot more - they got very close. Sandbagging or just careful scheduling of improvements?  Intentional or not, they did manage to surprise everyone with their evolution.

Interestingly, they're actually closer to ETNZ in the mid-range, not in the light. Maybe a good sign for them for today.

TR has superior Speed and TWA in most conditions (except for LR in mid-range upwind).

bs.thumb.png.ddd8b2bc26c4a4983be78d911b9ac915.png

rtwa.thumb.png.cf6b9e61bbbc7e703a19176e6eb6f170.png

 

AWA vs TWS:

awa.thumb.png.e2f8873eeb425709ad6115c3f78a6f3e.png

I guess it's not surprising it's the Kiwis who can sail with the tightest AWA in all conditions showing their superior efficiency and lift/drag ratios. Again, check out the improvement by LR!

Effective foil cant (heel+cant angle) vs TWS:

efcant.thumb.png.2c3633f3aa49e8f4c25b69b22cbf2d41.png

 I thought this was interesting how their techniques evolved. LR increased effective cant angles both up- and downwind, while ETNZ increased it downwind and in light upwind. AM were using some crazy angles in strong upwind. That's probably the batwing main / low CoE setup. I'd love to see what ETNZ would do in that range.

Pitch vs TWS:pitch.thumb.png.9be55154906aa112aa8b0d28df65bdbc.png

Pitch angle (positive is forward pitch here) doesn't really correlate with wind speed for most boats, but there are some interesting differences between the teams with AM and ETNZ sailing the most bow-down.

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Here is the data from the last race, just for the record. No surprises, ETNZ clearly dominated both upwind and downwind:

1590793199_uwvmg.png.fe7a58537ec33af6433fbdb4d01d9dfb.png938115219_dwvmg.png.5c9acb2cf2bce0edd0e7b6601fb29fba.png

They've sailed some amazing apparent angles:

1219733445_uwawa.png.c18f4e8fa7d5cfb70f0857f7fc8b9851.png807160785_dwawa.png.8aa17cbb5280d204da4fbe34725ede21.png

For me the most remarkable is how ETNZ switched to a whole new level of performance within a few days. The two boats were matched pretty good on the first two days, and then ETNZ figured out something. They not only started to tack better, but somehow found an extra gear in straight line speed.

I think this sums it up pretty well :D:

etnz.gif.9536abb18f8ed90dfff6726171ff2878.gif

What an amazing machine and a group of sailors / engineers who figured out how to tame it. Congrats to ETNZ!

Also thanks for everyone for all the wonderful discussions here. I've learned a lot.

 

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Core I hope all you geniuses keep analysing all this stuff and future stuff.

I for one will have a bit more time to go through all this amazing analysis and clear out my thoughts.

Then there will be the new boats (or maybe the new rules for these boats?).

Hope there is a new life for this thread/forum

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51 minutes ago, erdb said:

Here is the data from the last race, just for the record. No surprises, ETNZ clearly dominated both upwind and downwind:

1590793199_uwvmg.png.fe7a58537ec33af6433fbdb4d01d9dfb.png938115219_dwvmg.png.5c9acb2cf2bce0edd0e7b6601fb29fba.png

They've sailed some amazing apparent angles:

1219733445_uwawa.png.c18f4e8fa7d5cfb70f0857f7fc8b9851.png807160785_dwawa.png.8aa17cbb5280d204da4fbe34725ede21.png

For me the most remarkable is how ETNZ switched to a whole new level of performance within a few days. The two boats were matched pretty good on the first two days, and then ETNZ figured out something. They not only started to tack better, but somehow found an extra gear in straight line speed.

I think this sums it up pretty well :D:

etnz.gif.9536abb18f8ed90dfff6726171ff2878.gif

What an amazing machine and a group of sailors / engineers who figured out how to tame it. Congrats to ETNZ!

Also thanks for everyone for all the wonderful discussions here. I've learned a lot.

 

Thank you for the incredible data and insights you prepared for our benefit. Interesting that Dan Bernasconi admitted to being disappointed that we didn't get to see these AC75's in strong breeze. I suspect there were a few more surprises in store. 

In the aftermath of SFO, one key learning rammed home to all involved with ETNZ was the need to be able to improve performance through the match Final. And beyond race practice, which mattered, it suggests that they were tinkering every day to get better sailing/boat performance.

 

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2 hours ago, erdb said:

Here is the data from the last race, just for the record. No surprises, ETNZ clearly dominated both upwind and downwind:

1590793199_uwvmg.png.fe7a58537ec33af6433fbdb4d01d9dfb.png938115219_dwvmg.png.5c9acb2cf2bce0edd0e7b6601fb29fba.png

They've sailed some amazing apparent angles:

1219733445_uwawa.png.c18f4e8fa7d5cfb70f0857f7fc8b9851.png807160785_dwawa.png.8aa17cbb5280d204da4fbe34725ede21.png

For me the most remarkable is how ETNZ switched to a whole new level of performance within a few days. The two boats were matched pretty good on the first two days, and then ETNZ figured out something. They not only started to tack better, but somehow found an extra gear in straight line speed.

I think this sums it up pretty well :D:

etnz.gif.9536abb18f8ed90dfff6726171ff2878.gif

What an amazing machine and a group of sailors / engineers who figured out how to tame it. Congrats to ETNZ!

Also thanks for everyone for all the wonderful discussions here. I've learned a lot.

 

My thinking is that as they learnt to manouvre better, they were able to keep out of Luna Rossa's gas more often, freeing them up to realise the superior VMG they had to begin with.

But ya know, could be wrong :lol:

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5 hours ago, erdb said:

Here is the data from the last race, just for the record. No surprises, ETNZ clearly dominated both upwind and downwind:

1590793199_uwvmg.png.fe7a58537ec33af6433fbdb4d01d9dfb.png938115219_dwvmg.png.5c9acb2cf2bce0edd0e7b6601fb29fba.png

They've sailed some amazing apparent angles:

1219733445_uwawa.png.c18f4e8fa7d5cfb70f0857f7fc8b9851.png807160785_dwawa.png.8aa17cbb5280d204da4fbe34725ede21.png

For me the most remarkable is how ETNZ switched to a whole new level of performance within a few days. The two boats were matched pretty good on the first two days, and then ETNZ figured out something. They not only started to tack better, but somehow found an extra gear in straight line speed.

I think this sums it up pretty well :D:

etnz.gif.9536abb18f8ed90dfff6726171ff2878.gif

What an amazing machine and a group of sailors / engineers who figured out how to tame it. Congrats to ETNZ!

Also thanks for everyone for all the wonderful discussions here. I've learned a lot.

 

Thanks mate, keep them coming.

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5 hours ago, Paddywackery said:

Interesting that Dan Bernasconi admitted to being disappointed that we didn't get to see these AC75's in strong breeze. I suspect there were a few more surprises in store.

 

I'm in the camp that believes at the highest range (19-21 knots) LR might gain the advantage.   At top wind speeds, hydro drag becomes irrelevant since every boat is over powered/ over canvassed (hence the bat-wing sails and reverse camber on the mainsail head).   If boats are desperately trying to shed power, then the excess hydro drag from larger foils becomes moot. Right?

 

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21 minutes ago, Blitzkrieg9 said:

I'm in the camp that believes at the highest range (19-21 knots) LR might gain the advantage.   At top wind speeds, hydro drag becomes irrelevant since every boat is over powered/ over canvassed (hence the bat-wing sails and reverse camber on the mainsail head).   If boats are desperately trying to shed power, then the excess hydro drag from larger foils becomes moot. Right?

I don't think so. Boat speed is governed by forward Drive less Drag.

At any wind speed, there is a limit to the amount of sail force that can be balanced by the available RM.  If two boats can both manage the same amount of sail force, then the Drive vector will be the same (assuming same AWA etc), but boat speed will still be a factor of Drive less Drag.

Sadly, we'll never know for certain how TR and LR would have compared at those speeds.

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47 minutes ago, Blitzkrieg9 said:

I'm in the camp that believes at the highest range (19-21 knots) LR might gain the advantage.   At top wind speeds, hydro drag becomes irrelevant since every boat is over powered/ over canvassed (hence the bat-wing sails and reverse camber on the mainsail head).   If boats are desperately trying to shed power, then the excess hydro drag from larger foils becomes moot. Right?

 

Not convinced of that at all.

Being over canvassed is about too much power and not enough righting moment.

You can have 50 tonnes of force going into your rig, but if your foils are the shape and size of a hump backed whale, you're fucked.

Lets look at it this way:

1) Drag in turbulent flow is proportional to the square of the speed.

2) Larger foils generally should have a larger coefficient of drag. Push them uprange and according to #1, their disadvantage relative to smaller foils will increased squared rather than lineaely.

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21 minutes ago, MaxHugen said:

I don't think so. Boat speed is governed by forward Drive less Drag.

At any wind speed, there is a limit to the amount of sail force that can be balanced by the available RM.  If two boats can both manage the same amount of sail force, then the Drive vector will be the same (assuming same AWA etc), but boat speed will still be a factor of Drive less Drag.

Sadly, we'll never know for certain how TR and LR would have compared at those speeds.

Okay. So, my understanding is that with the 30% larger foils, LR can produce more RM overall.  But, in lighter winds, the RM isn't needed so all you get is extra drag. In other words, LR is "over foiled" (more foil and RM than they can use).  

ETNZ with smaller foils can't produce as much maximum RM, but that's fine because they rarely need it. So normally ETNZ has enough RM to capture all the available wind power AND they have less hydro drag.   

But it seems to me that at some high wind speed ETNZ foils are at maximum RM and can't utilize anymore wind...  so they have to spill it. But, with larger foils, LR has more RM potential so they CAN use the excess wind/power. 

I suppose my idea is predicated on the notion that LR foils have a greater RM potential. Maybe that supposition is erroneous. 

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7 hours ago, erdb said:

Here is the data from the last race, just for the record. No surprises, ETNZ clearly dominated both upwind and downwind:

1590793199_uwvmg.png.fe7a58537ec33af6433fbdb4d01d9dfb.png938115219_dwvmg.png.5c9acb2cf2bce0edd0e7b6601fb29fba.png

They've sailed some amazing apparent angles:

1219733445_uwawa.png.c18f4e8fa7d5cfb70f0857f7fc8b9851.png807160785_dwawa.png.8aa17cbb5280d204da4fbe34725ede21.png

For me the most remarkable is how ETNZ switched to a whole new level of performance within a few days. The two boats were matched pretty good on the first two days, and then ETNZ figured out something. They not only started to tack better, but somehow found an extra gear in straight line speed.

I think this sums it up pretty well :D:

etnz.gif.9536abb18f8ed90dfff6726171ff2878.gif

What an amazing machine and a group of sailors / engineers who figured out how to tame it. Congrats to ETNZ!

Also thanks for everyone for all the wonderful discussions here. I've learned a lot.

 

Always great data, thank you!

 

Is the vmg computed between twd measured at the boat(?) and:

Heading (bow compass angle)

Or

Gps track course angle

?

 

Thank you!

 

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5 minutes ago, Blitzkrieg9 said:

So, my understanding is that with the 30% larger foils, LR can produce more RM overall.

hang on that is only true in take off and minimal winds!    over a fairly low limit RM is weight weight of boat * distance to foil  size of foil completely irrelevant (to RM) in high winds

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9 minutes ago, Blitzkrieg9 said:

my idea is predicated on the notion that LR foils have a greater RM potential. Maybe that supposition is erroneous. 

yes  EXCEPT if they somehow are bringing the center of effort of the foil outboard

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6 hours ago, Paddywackery said:

 Interesting that Dan Bernasconi admitted to being disappointed that we didn't get to see these AC75's in strong breeze.

Yeah, I thought that was very funny. The only person in the team who was somewhat disappointed to finish the series. Hopefully we will see it next time.

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5 minutes ago, karlooie said:

Always great data, thank you!

 

Is the vmg computed between twd measured at the boat(?) and:

Heading (bow compass angle)

Or

Gps track course angle

?

 

Thank you!

 

VMG is calculated from TWD reported by the boat and its GPS track. Lots of room for error obviously and while I think the calibration got better over time, there still may be a bias in TR's data always shifting the TWD against them a little.

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15 minutes ago, breezie said:

hang on that is only true in take off and minimal winds!    over a fairly low limit RM is weight weight of boat * distance to foil  size of foil completely irrelevant (to RM) in high winds

That just can't be right.  Imagine your foil is the size of a pencil. My foil has the same weight as yours, dame shape as yours, but mine is the size of a door. Surely, my foil is creating more RM. 

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16 minutes ago, Blitzkrieg9 said:

So, my understanding is that with the 30% larger foils, LR can produce more RM overall.  

 

8 minutes ago, breezie said:

hang on that is only true in take off and minimal winds!    over a fairly low limit RM is weight weight of boat * distance to foil  size of foil completely irrelevant (to RM) in high winds

It's not the foil area that makes a difference in righting moment, but the anhedral of the Y foil. Once the boats are foiling, the foil area makes no difference in righting moment.

I've posted this before to show that the Y foil can generate more righting moment allowing a higher CoE on the sails for the same lateral sail force. However, as the wind gets stronger, the difference in max righting moment between T- and Y-foil diminishes. At the max wind speed limit with a lateral sail force of ~50kN, the righting moment would be about the same for both foils.

top2.thumb.png.391ddaec40f5cddeb6944119c6977918.pngrm.png.cc5a13a4df13630690a1ced6f273e534.png

 

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1 minute ago, erdb said:

 

It's not the foil area that makes a difference in righting moment, but the anhedral of the Y foil. Once the boats are foiling, the foil area makes no difference in righting moment.

I've posted this before to show that the Y foil can generate more righting moment allowing a higher CoE on the sails for the same lateral sail force. However, as the wind gets stronger, the difference in max righting moment between T- and Y-foil diminishes. At the max wind speed limit with a lateral sail force of ~50kN, the righting moment would be about the same for both foils.

top2.thumb.png.391ddaec40f5cddeb6944119c6977918.pngrm.png.cc5a13a4df13630690a1ced6f273e534.png

 

yeah :)

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8 minutes ago, Blitzkrieg9 said:

Which, I believe LR can do greater than ETNZ with a y-foil and separate control surfaces...

Yes, differential flap settings can move the Vertical force CE further outboard, but not by much.

Then you need to consider the drag penalty from using the flaps like this, and weigh up advantage vs disadvantage.

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1 hour ago, Blitzkrieg9 said:

...At top wind speeds, hydro drag becomes irrelevant since every boat is over powered/ over canvassed (hence the bat-wing sails and reverse camber on the mainsail head).   If boats are desperately trying to shed power, then the excess hydro drag from larger foils becomes moot. Right?

 

51 minutes ago, Blitzkrieg9 said:

Okay. So, my understanding is that with the 30% larger foils, LR can produce more RM overall.  ...

I don't believe either of these statements are true.  Foil profile drag (which is mostly skin friction) increases with the square of the speed, while lift-induced drag decreases with the square of the speed.  So foil area matters more at high speed.

The larger foils do not give LR more righting moment.  The righting moment is the lift times the moment arm, and the lift essentially equals the weight.  So more foil area means the foil produces the same lift at a lower angle of attack (or with less flap deflection) than for a smaller foil.  But the righting moment is the same because the foils are constrained to have the same span and arm length.

Where the larger foils may be useful at high speed is in pushing out the onset of cavitation.  If two foils have the same physical thickness, then the larger chord will give the foil a smaller thickness ratio and this will lower the velocities on the foil and can raise the cavitation speed.  Of course, if the larger foil has a larger physical thickness in order to hold the ballast or flap controls, that will negate the cavitation advantage.

As I posted earlier, it would be interesting to compare the wetted aspect ratio of the two foils.  Or, since the span is the same, just the wetted area of the wing, bulb, and immersed strut.  That will tell you more about the high speed drag difference than just the planform area.

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^ Did a couple of diagrams showing the difference in CEs when using differential flaps. They assume that 70,000N of Vertical force (Fz) is required to balance boat mass:

Capture.JPG.ffed6eb702e4587f7099cfc9e8c759c7.JPG

Then differential flaps are applied. Still need a total of 70,000N Fz, but the leeward foil wing has extra flap to create more Fz there, and windward flap is reduced so total is still 70kN.  CE-Fz has moved outboard a bit, but Fy is reduced.

Capture.JPG.28d30a9274cef6944ff6c42d6d28653d.JPG

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24 minutes ago, Basiliscus said:

Where the larger foils may be useful at high speed is in pushing out the onset of cavitation.  If two foils have the same physical thickness, then the larger chord will give the foil a smaller thickness ratio and this will lower the velocities on the foil and can raise the cavitation speed.  Of course, if the larger foil has a larger physical thickness in order to hold the ballast or flap controls, that will negate the cavitation advantage.

As I posted earlier, it would be interesting to compare the wetted aspect ratio of the two foils.  Or, since the span is the same, just the wetted area of the wing, bulb, and immersed strut.  That will tell you more about the high speed drag difference than just the planform area.

So how do you think ETNZ managed to get away with much smaller foils? Based on your cavitation analysis you've posted here earlier, it seems they should have some serious cavitation issues both at low and high speeds. Yet, they seemed to take off and foil just fine in the light air, and they certainly didn't seem to have problems going fast either.

Do you see anything unique in their foil design that probably solved those issues?

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1 hour ago, Blitzkrieg9 said:

Okay. So, my understanding is that with the 30% larger foils, LR can produce more RM overall.  But, in lighter winds, the RM isn't needed so all you get is extra drag. In other words, LR is "over foiled" (more foil and RM than they can use).  

ETNZ with smaller foils can't produce as much maximum RM, but that's fine because they rarely need it. So normally ETNZ has enough RM to capture all the available wind power AND they have less hydro drag.   

But it seems to me that at some high wind speed ETNZ foils are at maximum RM and can't utilize anymore wind...  so they have to spill it. But, with larger foils, LR has more RM potential so they CAN use the excess wind/power. 

I suppose my idea is predicated on the notion that LR foils have a greater RM potential. Maybe that supposition is erroneous. 

LRs foils have more lift, but I'm not sure they would do much for righting moment because they are providing lift.

I suggest you watch @Mozzy Sails vids, particularly the one about righting moment. Really well done.

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4 minutes ago, erdb said:

So how do you think ETNZ managed to get away with much smaller foils? Based on your cavitation analysis you've posted here earlier, it seems they should have some serious cavitation issues both at low and high speeds. Yet, they seemed to take off and foil just fine in the light air, and they certainly didn't seem to have problems going fast either.

Do you see anything unique in their foil design that probably solved those issues?

I've not seen anything published that has enough detail to be able to say how they did it.  I'm pretty sure their foils were physically thinner than LRPP's, but I don't know about the thickness ratio.

The analysis I presented was concerned with the range of speeds for which cavitation cannot occur, because I have no way of predicting what happens after the onset of cavitation.  A team with a sophisticated multi-phase CFD capability might be able to design shapes that could push into the cavitation range with an acceptable penalty to lift and drag.

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