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1 hour ago, MaxHugen said:

I'm not yet convinced that GB is using negative lift on the windward foil. To do this would place quite a burden on the flight controller. As they approach where they want to gybe, they put the port foil down, and both have to be adjusted to share the required lift. This must be maintained as they go through the gybe, and only then could they apply negative lift to the windward foil. At the same time the leeward foil has to compensate by increasing lift to100% required lift plus the negative lift.

Stepping through frame by frame you can see that the heel had already increased to 4° before the starboard (windward) foil was lifted.

image.png.bb2fdc3cea71cf35957547436fe47b96.png

Another explanation for heel could of course be mainsail trim.

I've just watched the feed again and I agree they were already heeling. It looks like maybe the main didn't go out fast enough? It is interesting to note that they ease the sheet before the traveler which is unusual for controlling heel.

2 hours ago, MaxHugen said:

At the same time the leeward foil has to compensate by increasing lift to100% required lift plus the negative lift.

I don't think the leeward foil has any extra work to do if the windward foil is producing negative lift. The windward foil producing negative lift is acting as righting moment. It is something that I know has been played with on foiling cats, and the theory all works but its very tricky to do if you don't have proper control over the foil. I think that with a flight controller, it is likely that teams are using the windward foil to control the heel in moments like these. Nathan Outteridge touched on it with his interviews on Planet Sail (link), I think it's around the 12 minute mark.

In fact Nathan talks about a scenario exactly like this one with Ineos, where if you have negative lift on the windward board and you bring it out, the boat will get blown over. 

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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

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3 hours ago, MaxHugen said:

I'm not yet convinced that GB is using negative lift on the windward foil. 

Another explanation for heel could of course be mainsail trim.

Giles literally said so in the post race press conference.

The main was trimmed on hard and the flight controller must have gone negative to compensate. BA called for the foil up and the heel drastically accelerated soon after.

But yes, ultimately the main was the reason heel, as it should have been eased so the windward foil could go neutral before being lifted. No idea how they coordinate that normally, i watched their JK from stern camera and it wasn't clear.

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AC75 foil wing section design, part 5

So far, cavitation has been like the Star Wars trash compactor, putting the squeeze on the speed range from both ends.  The tentacles reaching up to pull the design down into the muck are the various sources of drag.  And profile drag is all about the development of the boundary layer.

Absent cavitation or flow separation, the principal source of profile drag is skin friction.  When the boundary layer is laminar, the skin friction is low.  Once it transitions to turbulent flow, the mixing produced by eddies brings higher speed flow closer to the surface and raises the skin friction. So the farther back laminar flow can be maintained, the lower the skin friction will be.  This also delays the growth of the turbulent boundary layer and minimizes the pressure drag from the boundary layer effectively changing the shape of the section.

Xfoil uses the e^n method to predict when transition will occur.  This is based on the idea that the water the foil is flying through is not perfectly still, but has eddies and other small motions.  These disturb the boundary layer as they get swept into it.  The boundary layer itself can amplify or dampen these disturbances.  If the disturbances reach a critical size, the flow will become nonlinear and generate eddies of its own, becoming turbulent.  If the disturbances are initially very small, then they have to be amplified a great deal to reach the critical size.  But if they are much larger already when they enter the boundary layer, then they need only be amplified a modest amount before they become critical and transition occurs.  Xfoil allows one to assume what the amplification factor is (actually the logarithm of the amplification factor) with the parameter Ncrit.  Ncrit is the critical value of the exponent when the critical amplification factor is represented as e^Ncrit.  This is how Xfoil accounts for the effects of the external flow conditions on boundary layer transition.

A favorable pressure gradient will dampen disturbances in the boundary layer and extend laminar flow.  An adverse pressure gradient will amplify disturbances and lead to earlier transition.  If the adverse pressure gradient leads to laminar separation, the separated flow is highly unstable and transition will occur very quickly, leading to turbulent reattachment (if the adverse pressure gradient is not too severe) forming a laminar separation bubble.  So the two main routes to transition on these wings are linear amplification of disturbances or the formation of a laminar separation bubble.

The proper value to use for Ncrit is hotly debated.  Anecdotal evidence, much of it based on hot film experiments on IACC keel bulbs, has transition occurring at lower Reynolds numbers in water compared to air.  This could be due to lots of factors, such as turbulence from wave action, and contaminants like air bubbles or sediment.  It could even change from day to day, as the sea state changes or runoff washes more sediment into the water.  The prudent thing to do is to run all the calculations assuming a range of values for Ncrit.

Here are the polars for the H142 section with undeflected flap.  The Reynolds numbers are based on the average chord of 410 mm, and are varied with speed according to the design loading of 49 kN/m^2.  The red curves have the boundary layer tripped to be fully turbulent.  The plot on the right side for each case shows where transition is occurring on the upper and lower surfaces.  As the angle of attack increases, the changes in slope of the pressure distribution drive transition forward on the upper surface and back on the lower surface.  The laminar boundary layer is not able to negotiate the hinge line on the lower surface, which is why all of the transition lines congregate there.  

plot_poloar_H142_p7003rxx_r38e5IInx_Page_5.thumb.png.834ce063e20d8e26a9972c9a4470eacf.png

There is potentially a saving in drag upwards of 25% at the high speed CL of 0.2, and more at somewhat lower speeds.  If the laminar flow can be realized and Ncrit turns out to be high.  Conjuring Dirty Harry, "You've got to ask yourself one question. Do I feel lucky?"  Laminar flow requires total commitment by the whole team - it's not just a design choice.  The foils have to be accurately constructed to the design shape.  The surface has to be smooth, free of waviness, and polished.  And it has to be maintained in pristine condition.

Here are the polars for the other flap deflections. The humps and hollows in the drag curves are due to rapid changes in the transition location with angle of attack that change the proportion of laminar vs turbulent extents of the boundary layer.

-5 deg flap

plot_poloar_H142_p7003rxx_r38e5IInx_Page_6.thumb.png.676ac75d97e976d16e0cae53f454735a.png

+5 deg flap:

plot_poloar_H142_p7003rxx_r38e5IInx_Page_7.thumb.png.0af108b89a459d0f1ffef435e7cc957b.png

10 deg flap:

plot_poloar_H142_p7003rxx_r38e5IInx_Page_4.thumb.png.a849a6ae688e6c5068b795e92cd08452.png

Here are the various flap deflections assuming the boundary layer is fully turbulent:

plot_poloar_H142_p7003rxx_r38e5IInx_Page_1.thumb.png.e59353acfa85bdf5747b6a5292e7b0f4.png

Assuming Ncrit = 1, with free transition:

plot_poloar_H142_p7003rxx_r38e5IInx_Page_2.thumb.png.f3a6a49fac7ae9d150cdde54aa423b81.png

Assuming Ncrit = 3

plot_poloar_H142_p7003rxx_r38e5IInx_Page_3.thumb.png.5bf24fe76ba2d42cd8800e1158ade21f.png

Assuming Ncrit = 5

plot_poloar_H142_p7003rxx_r38e5IInx_Page_4.thumb.png.a849a6ae688e6c5068b795e92cd08452.png

My guess, and it's only a guess, is Ncrit will be somewhere between 1 and 3.  I wouldn't bet on it being higher than that, but teams may have better information than I do.

Next up:  Going thinner.

plot_poloar_H142_p7003rxx_r38e5IInx_Page_8.png

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I think you're beginning to see how the uncertainties multiply in the design process.  At first we only had to be concerned with shaping for low- and high-speed cavitation at potential flap angles.  Now we're starting to be concerned with drag, too, and that means we need to take into account a range of ambient conditions.  And so far, it's only been about one section, the average chord.  There will need to be sections designed at a half dozen or more spanwise locations.  The number of case that need to be run multiplies quickly.

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4 hours ago, JoeW said:

I've just watched the feed again and I agree they were already heeling. It looks like maybe the main didn't go out fast enough? It is interesting to note that they ease the sheet before the traveler which is unusual for controlling heel.

I don't think the leeward foil has any extra work to do if the windward foil is producing negative lift. The windward foil producing negative lift is acting as righting moment. It is something that I know has been played with on foiling cats, and the theory all works but its very tricky to do if you don't have proper control over the foil. I think that with a flight controller, it is likely that teams are using the windward foil to control the heel in moments like these. Nathan Outteridge touched on it with his interviews on Planet Sail (link), I think it's around the 12 minute mark.

In fact Nathan talks about a scenario exactly like this one with Ineos, where if you have negative lift on the windward board and you bring it out, the boat will get blown over. 

Thanks, I'll check out Nathan's comments.

Note that there are forces, which are calculated in 3 directions: x (longitudinal), y (lateral) and z (vertical).  The ± vertical force(s) of one (or both) of the foils has to equal the mass of the boat ± the lift/downforce of the rudder foil for a balanced state.

These 3 directional forces also produce 3 "turning" forces, which are the moments. You're right, that any ± moment produced by the windward foil does not affect the leeward foil (which is generally considered the axis of rotation).

But as a force in the z direction, any downward force of the windward foil has to be countered by the leeward foil - or the boat would descend back to displacement mode.

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3 hours ago, sfigone said:

Giles literally said so in the post race press conference.

The main was trimmed on hard and the flight controller must have gone negative to compensate. BA called for the foil up and the heel drastically accelerated soon after.

But yes, ultimately the main was the reason heel, as it should have been eased so the windward foil could go neutral before being lifted. No idea how they coordinate that normally, i watched their JK from stern camera and it wasn't clear.

Giles didn't specifically say the windward foil was producing downward force...

GS: "Ultimately the windward board breached the surface and that resulted in a big leeward heel."

Although it does seem to imply that.

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1 hour ago, Basiliscus said:

I think you're beginning to see how the uncertainties multiply in the design process.  At first we only had to be concerned with shaping for low- and high-speed cavitation at potential flap angles.  Now we're starting to be concerned with drag, too, and that means we need to take into account a range of ambient conditions.  And so far, it's only been about one section, the average chord.  There will need to be sections designed at a half dozen or more spanwise locations.  The number of case that need to be run multiplies quickly.

Thanks, I really enjoy these posts.

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2 hours ago, Basiliscus said:

I think you're beginning to see how the uncertainties multiply in the design process.  At first we only had to be concerned with shaping for low- and high-speed cavitation at potential flap angles.  Now we're starting to be concerned with drag, too, and that means we need to take into account a range of ambient conditions.  And so far, it's only been about one section, the average chord.  There will need to be sections designed at a half dozen or more spanwise locations.  The number of case that need to be run multiplies quickly.

I've been using Ncrit=9 for both the sails and the foils in XFoil, having assumed a high level of turbulence for both. Considering your discussion regarding the different turbulence conditions of water vs air, should I theoretically use a lower Ncrit for air?

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4 hours ago, MaxHugen said:

Giles didn't specifically say the windward foil was producing downward force...

GS: "Ultimately the windward board breached the surface and that resulted in a big leeward heel."

Although it does seem to imply that.

 

That's not what he said.   He said:

"Ultimately um the windward board would have been pulling down and it breached the surface and that resulted in ah in a big uh big heel"

 

 

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On 2/14/2021 at 12:55 AM, erdb said:

 

So yeah you were right. Something is weird with LR's instruments. I checked, and they had the same issue in the semis, too. I don't know how this happens, because the error is not symmetric. Anyway, here is upwind leeway on port and starboard - pretty much the same for INEOS, but messed up for LR:

1906546823_uw_portleeway.png.1925cc0cd270c84ac876154cc6da27b9.png   1566238557_uw_strleew.png.6dd5d15a9ecf6687ab37251cf1d6bdf2.png

Same thing downwind (port and starboard):

86622553_dw_portleeway.png.966a860ba4849ce93fc06f88fab453b8.png   2052614148_dw_strleew.png.a11f19571ac0abc96c07b4d20547c499.png

 

I had to mess with my code to get them separately, but once there, I thought at least I could look at JS vs Bruni. It's kind of silly, because currents, waves (and calibration issues - grrr) can make the course/numbers asymmetric, but here it is (from Race-2):

Upwind VMG port and starboard. The funny thing is that it's INEOS that shows a difference. On port, they actually matched LR's upwind VMG, on starboard, they were slower.

550502459_uw_portvmg.png.f8318bfa5a32051981309689be09d8b7.png   199196057_uw_strvmg.png.bb4f756aebe326654dd14f1778eeaf27.png

Downwind VMG port and starboard. Here, it's reversed, INEOS is better on starboard, LR is better on port. :blink:

710148988_dw_portvmg.png.d0755c0d54d357550faa48953c9c6fc5.png  144501685_dw_strvmg.png.ef51b515b1802aaef0fb5829da531682.png

Thanks for this. 

Is leeway corrected for tack. Or is port tack always negative and starboard positive (for example)? So the twin peaks we saw for LR were the same leeway, but on the two different tacks?

Whereas INEOS see asymmetric? 

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3 hours ago, sfigone said:

That's not what he said.   He said:

"Ultimately um the windward board would have been pulling down and it breached the surface and that resulted in ah in a big uh big heel"

My apologies, you are correct.  I had previously taken some notes by both BA and GS from that press conference as I was interested in the cause. Should have re-checked the video. :unsure:

Been wondering if there were any similar contributory factors between GB's leap, and AM's capsize. Could this have also been partially responsible for AM's heel prior to loss of control, as well as reduced speed, backstay, and a gust?

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11 hours ago, MaxHugen said:

I've been using Ncrit=9 for both the sails and the foils in XFoil, having assumed a high level of turbulence for both. Considering your discussion regarding the different turbulence conditions of water vs air, should I theoretically use a lower Ncrit for air?

Ncrit=9 is Xfoil's default value, and it is appropriate for airfoils at high altitude.  It corresponds to ambient turbulence values that are less than 0.1% of the freestream.  Here are some values of Ncrit and their associated turbulence levels:

9.00   ( 0.070 % turb. level )
5.00   ( 0.371 % turb. level )
3.00   ( 0.854 % turb. level )
1.00   ( 1.966 % turb. level )

The main thing is not what the actual turbulence levels are, but picking Ncrit so the transition location matches experiment, as it is the main means in Xfoil of adjusting transition.

I don't know what the right value is for foils in Auckland.  I suspect it is somewhere between 1 and 3, but that's just a guess.  I think Mark Drela uses at least 5 - 7 for model airplanes, so that may be appropriate for sails, as both are operating in the near-ground atmosphere.  

As a practical matter, I don't see how there would be any laminar flow past the mast/sail junction, due to the roughness of the junction.  So I would artificially trip the flow there.

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47 minutes ago, Basiliscus said:

Ncrit=9 is Xfoil's default value, and it is appropriate for airfoils at high altitude.  It corresponds to ambient turbulence values that are less than 0.1% of the freestream.  Here are some values of Ncrit and their associated turbulence levels:

9.00   ( 0.070 % turb. level )
5.00   ( 0.371 % turb. level )
3.00   ( 0.854 % turb. level )
1.00   ( 1.966 % turb. level )

The main thing is not what the actual turbulence levels are, but picking Ncrit so the transition location matches experiment, as it is the main means in Xfoil of adjusting transition.

I don't know what the right value is for foils in Auckland.  I suspect it is somewhere between 1 and 3, but that's just a guess.  I think Mark Drela uses at least 5 - 7 for model airplanes, so that may be appropriate for sails, as both are operating in the near-ground atmosphere.  

As a practical matter, I don't see how there would be any laminar flow past the mast/sail junction, due to the roughness of the junction.  So I would artificially trip the flow there.

The mast/sail junction is at about 9% of chord from the LE.  What would be the TripLocation value for this pls?  Can't find an explanation in the XFoil docs.

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AC75 foil wing section design, part 6

In light of the free transition results in my last post, I've made another iteration on the section design.  I reduced the thickness from 12% to 11% to bump up the high-speed cavitation, and I gave the rooftop on the pressure distribution a small favorable slope to encourage laminar flow.  I still think the flap is probably too thin to be practical.  Here's what the new shape looks like:

plot_H143_p7003rxx_r38e5IInxx_Page_1.thumb.png.7855d1af36dfccca02e347095e723411.png

As before, the design pressure distribution has no net lift over the forward half of the section:

plot_H143_p7003rxx_r38e5IInxx_Page_2.thumb.png.4668a8b8356d81ac3680bd8dad846696.png

I also ensured the leading edge pressure peak wasn't too high at the takeoff condition:

plot_H143_p7003rxx_r38e5IInxx_Page_3.thumb.png.b1e9023b32573162e7286925f457cfdd.png

A comparison of the profile drag with the previous section showed a savings of about 11 counts (more than 12%)  for both fixed and free transition at high-speed: 

plot_polar_H143vsH142_r38e5IInxx_Page_1.thumb.png.08c1d2901b2e91ba01291f3a59478afa.png

Here are the polars assuming Ncrit=3 for all the flap deflections:

plot_polar_H143_p7003rxx_r38e5IInxx_Page_3.thumb.png.e1feb48b4eb5877878104aa4f6a04ea3.png

The cavitation envelopes show the cavitation speed is an honest 45 kt, now, and at a slightly higher loading that would allow increasing the loading from 49 kN/m^2 to 52 kN/m^2, saving another 6% in profile drag.  The higher loading might need a bit of a tweak to the leading edge shape for the higher takeoff CL.

H143_Cavitation.thumb.png.95c23b35e060ba23b7b208950fd24597.png

I think I'm going to leave it here.  This idiot needs his village to provide guidance as to where the design needs to be improved in order to make things feasible for the other engineering disciplines.

The main points I've tried to make with these posts are:
- Cavitation drives the hydrofoil section design at both high and low speeds
- The local velocities due to thickness make it hard to have thick sections for structural stiffness and ballast volume, while still having cavitation onset speeds above 40 kt.
- At high speed, the forward half of the section has very similar pressures on both surfaces, with all of the lift generated by the aft half of the foil, especially the flap. 
- As a result, the shape of the forward half of the section is nearly symmetrical. 
- Given that the heaviest part of the section shape is essentially dictated by the physics, the 20% rule allows for considerable tailoring of the section by swapping out flaps.
- Inverse design methods, like those of Xfoil, are essential to producing sections that are tailored to the specific design requirements.  No team will be using off-the-shelf NACA or Eppler sections, although those may provide reasonable starting points.
- The AC75s are operating near the edges of what is physically possible in hydrofoil design.

For those interested in playing with this shape, I've attached a zip file with the section coordinates and polar data.

 

H143_Data.zip

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1 minute ago, MaxHugen said:

The mast/sail junction is at about 9% of chord from the LE.  What would be the TripLocation value for this pls?  Can't find an explanation in the XFoil docs.

Yes.  Go to OPER->VPAR->X.  Positive values of the trip location are distances from the leading edge.  Negative values are distances from the stagnation point.  The latter can be helpful when working with high lift sections that have the stagnation point well to the windward side of the leading edge.

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1 minute ago, Basiliscus said:

Yes.  Go to OPER->VPAR->X.  Positive values of the trip location are distances from the leading edge.  Negative values are distances from the stagnation point.  The latter can be helpful when working with high lift sections that have the stagnation point well to the windward side of the leading edge.

So for 9% from the LE,  should I use the value 9.0, or 0.09? 

(I don't know the 'range')

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23 minutes ago, Basiliscus said:

I think I'm going to leave it here.... 

Difficult question from one village idiot to another.   With the work you've done on foils, how practical do you think it would be to make a foiler for us common folk?   

Just ball park calculations, do you think it possible to make foils for a 10m boat of about 1200KG (excluding a keel or weighted foils) with 350Kg crew weight? For simplicity, let's say the boat has 2 fixed foil arms, with both foils can be used for take off and then once going the leeward foil only would be used for lift and the windward one neutral or negative.

Such a boat should be able to achieve 10kn boat speed in displacement mode in moderate winds, so if you don't care about max speed, are there foils that could produce enough lift to take off at that speed?    

 

 

 

 

 

 

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I definitely think that in manoeuvres like that, the WW board is being used to produce RM. I assume when Ben called for board up, the flight controller went neutral flap and board up, assuming the mainsheet would take over the heel control.

7 hours ago, MaxHugen said:

My apologies, you are correct.  I had previously taken some notes by both BA and GS from that press conference as I was interested in the cause. Should have re-checked the video. :unsure:

Been wondering if there were any similar contributory factors between GB's leap, and AM's capsize. Could this have also been partially responsible for AM's heel prior to loss of control, as well as reduced speed, backstay, and a gust?

It doesn't look like AM were using the WW board for negative lift before their capsize. If you watch the replays, they are stable when the board comes up, using the main to control the heel.

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11 minutes ago, JoeW said:

It doesn't look like AM were using the WW board for negative lift before their capsize. If you watch the replays, they are stable when the board comes up, using the main to control the heel.

?  AM had quite a lot of heel right after the maneuver, and the mainsail was restricted due to the leeward backstay.

image.png.f71bcad64155f3aa6c21a903fe167fff.png

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52 minutes ago, sfigone said:

Difficult question from one village idiot to another.   With the work you've done on foils, how practical do you think it would be to make a foiler for us common folk?   

Just ball park calculations, do you think it possible to make foils for a 10m boat of about 1200KG (excluding a keel or weighted foils) with 350Kg crew weight? For simplicity, let's say the boat has 2 fixed foil arms, with both foils can be used for take off and then once going the leeward foil only would be used for lift and the windward one neutral or negative.

Such a boat should be able to achieve 10kn boat speed in displacement mode in moderate winds, so if you don't care about max speed, are there foils that could produce enough lift to take off at that speed?    

 

 

 

 

 

 

You can make anything foil if you get the right weight and enough power. Whether it is any good or worth doing is another matter!

I don't know whether there is much of a trickle down effect from these boats. An engineer on ETNZ I spoke to said they are basically using production parts which are already readily available and slightly adapting them as required. There isn't really that much development in terms of the foil systems.

I think it is still going to be expensive to get foiling for a while yet. If you want decent foils for a Moth then you're looking at over £3k for a main foil (horizontal and vertical) and £2.5k for a rudder foil (horizontal and vertical). Its going to be a lot of cash to get a boat that size foiling, especially using flap technology and with well made foils. You also have to think about how the boat is going to take this force. You'll probably need a huge amount of reinforcement both to take the load from the foil and to make the boat durable through crashes. I can see the cost increasing very quickly the more I think about it! I saw this image from an RS Aero which was using an adaptive foiling kit - maybe just goes to show how you need a boat designed for it...

 

More likely, I would expect to see the Imoca 60 foils trickle down to keelboats/yachts more. I think the most limiting factor of the inverted T foil style is sailor ability. You really have to keep the boat balanced to stay on the foils. We saw what happens when you get too much heel from Ineos the other day and AM earlier last month. The curved foils on the Imocas seem to be a lot more forgiving and user friendly. 

IMG_0154.JPG

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2 minutes ago, MaxHugen said:

?  AM had quite a lot of heel right after the maneuver, and the mainsail was restricted due to the leeward backstay.

image.png.f71bcad64155f3aa6c21a903fe167fff.png

If you look just before that, they are flat for a couple of seconds before they bear away. I do not think it is the same as Ineos because there is no immediate leeward heel, if you watch the onboard, the boat stays relatively flat through the board up, and only heels excessively when they bear away. I think Terry said the backstay was released as normal, but due to other factors the backstay became an issue and pinned the main in. 

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1 hour ago, sfigone said:

Difficult question from one village idiot to another.   With the work you've done on foils, how practical do you think it would be to make a foiler for us common folk?   

Just ball park calculations, do you think it possible to make foils for a 10m boat of about 1200KG (excluding a keel or weighted foils) with 350Kg crew weight? For simplicity, let's say the boat has 2 fixed foil arms, with both foils can be used for take off and then once going the leeward foil only would be used for lift and the windward one neutral or negative.

Such a boat should be able to achieve 10kn boat speed in displacement mode in moderate winds, so if you don't care about max speed, are there foils that could produce enough lift to take off at that speed?    

I don't know about your specs, but there are lots of foiling sailboats available.  The range from Dave Clark's UFO to beach cats (IFly15, WhisperETF26, Viper, many more) to the GC32, TF10G4.  If you want a monohull, there's the Quant 23.  With a 10m length, you're talking a daysailer and not a cruiser or open ocean racer, and a lot of people have put a lot of time and money developing foiling daysailers.  I think the GC32 comes closest to your specs.

Personally, I think a multihull is the way to go, rather than a ballasted monohull.  There are a lot of reasons for this, among them having maximum righting moment to accelerate to takeoff, and not having to lift ballast.  

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11 hours ago, Mozzy Sails said:

Thanks for this. 

Is leeway corrected for tack. Or is port tack always negative and starboard positive (for example)? So the twin peaks we saw for LR were the same leeway, but on the two different tacks?

Whereas INEOS see asymmetric? 

Do you think LR may be running an asymmetric foil setup? It's either that or their compass is off a little.

I checked my code again, everything seems to be correct. Yes, I flip the tacks, so positive leeway always means the same ("sliding" to leeward relative to centerline).

Weirdly, this split with leeway between port vs starboard only happens with LR. My first reaction was that I surely screwed up something, but look at these graphs from "Race-19":

Upwind leeway both tacks, port only, starboard only:

625429360_uwleewboth.png.d44354a9c1c6452d0ca4f3e99b0476f1.png  1218783708_uwleewp.png.303a68a1be73fe596cd4e633d76ff9d5.png  1255428828_uwleewsb.png.fdcb0612b236e59ecfe31132ffa37605.png

Leeway is exactly the same for INEOS on both tacks. LR has the same +2 deg leeway on starboard, but -0.8 deg on port.

Looks similar downwind:

both tacks, port only, starboard only:

1735979706_dwleewboth.png.e6b0bf45404e2d08eb3d2e9da2911e2b.png  701478645_dwleewp.png.13b4c6bc1c36d3534a231d4299b5235b.png  740017487_dwleewsb.png.2966df01050c6d10b97d420a6bac5e86.png

On starboard, both INEOS and LR have positive leeway, although LR's angle is a little higher. On port, INEOS has pretty much the same leeway as on starboard, but once again LR has negative leeway on port (-1.2 deg).

I've checked all the other races for LR going back to RR3, and they always have negative leeway on port.

So it's either their compass is slightly off, and it hasn't been touched since RR3, or there is a slight difference between the two sides in foil to foil arm angle or a foil profile / flap shape. Or maybe it's JS vs Bruni!  One likes to pull the flap lever harder! :D

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Data from Prada Final day 2:

LR still has a very very small advantage upwind (VMG, Race-1, Race-2):

387592736_uwvmg.png.314f7c6408a1fbab05b22580b6493838.png   2038453194_uwvmg.png.d6bf5ed95640f5df2c34da1cd77c4487.png

Very close downwind (VMG, Race-1, Race-2):

1109450126_dwvmg.png.b6a37aa8786a638dbb7e9e2a77ada619.png  1818007179_dwvmg.png.599e74f68a89512d2fbee909a43a67e2.png

As it has been discussed, there seems to be a difference in how much speed / distance is lost during tacks. INEOS loses ~10 m distance more towards the mark while tacking.

Race 1, Race 2:

vmgs.png.7464aaee366aedcc59351c8d91deb52c.png vmgs.png.ab39ddfdc9df6ccdd36b796ba4ad1618.png

Mozzy speculated that it was how they lift the windward foil after tack. To me the difference in how they change cant angle on the new foil seems much more significant:

INEOS kept the cant angle in the lower acceleration setting longer (Race 1, Race 2):

cant.png.012f91c5a50f93821c0e3c8d51a6f756.pngcant.png.75c579923a7e1ab181b42c7f61c24f6e.png

Of course that could be because it takes longer for them to accelerate (boat speed, Race 1, Race 2). So maybe more of a sail design/trim problem.

bs2.png.61d1c93ea78e79944ebbd01a8af1e936.png  bs.png.02761542ed8edfe5bfc0301dedefd32f.png

 

dw vmg.png

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9 hours ago, erdb said:

Mozzy speculated that it was how they lift the windward foil after tack. To me the difference in how they change cant angle on the new foil seems much more significant:

INEOS kept the cant angle in the lower acceleration setting longer (Race 1, Race 2):

cant.png.012f91c5a50f93821c0e3c8d51a6f756.pngcant.png.75c579923a7e1ab181b42c7f61c24f6e.png

 

 

The ERDB, you never fail! 

We know LR raced with odd foils early in the RR... could they really still be on odd foils now? It's quite a major difference between tacks. You would think negative leeway would be pretty horrible from a sail plan point of view... Perhaps their compass is just off centreline by 1.5 degree, and instead they sail with 0.5 degrees positive leeway?

Other than being stuck with partially upgraded technology I can't really think of a reason why a team would want to be asymmetric like this. It's not like we have asymmetric courses like in AC34+35. 

I did in my video actually suggest the foil drop was important too and highlighted the difference I saw in the data. I was seeing in race 19 and 20 that LR drop the new foil deeper, then raise a degree whereas INEOS just drop to the set point. Not seeing the longer build for INEOS, but, it was windier. Can you do the plots of both foils for Race 18? Maybe just the first couple of tacks?

Also, one other question, is 30sec centred on head to wind (TWA = Heading)? 

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9 hours ago, Mozzy Sails said:

The ERDB, you never fail! 

We know LR raced with odd foils early in the RR... could they really still be on odd foils now? It's quite a major difference between tacks. You would think negative leeway would be pretty horrible from a sail plan point of view... Perhaps their compass is just off centreline by 1.5 degree, and instead they sail with 0.5 degrees positive leeway?

Other than being stuck with partially upgraded technology I can't really think of a reason why a team would want to be asymmetric like this. It's not like we have asymmetric courses like in AC34+35. 

I did in my video actually suggest the foil drop was important too and highlighted the difference I saw in the data. I was seeing in race 19 and 20 that LR drop the new foil deeper, then raise a degree whereas INEOS just drop to the set point. Not seeing the longer build for INEOS, but, it was windier. Can you do the plots of both foils for Race 18? Maybe just the first couple of tacks?

Also, one other question, is 30sec centred on head to wind (TWA = Heading)? 

Yeah, who knows. I just checked what happens if I artificially shift the compass numbers by a few degrees, and it causes a similar double-peak distribution in leeway, so it could be just an off center compas, but from the data, we can't really tell for sure. For what it's worth, I looked at the foil cant angles port vs starboard as well. There may be a small difference upwind. This is from "Race-19" upwind cant 1) both tacks, 2) port only, 3) starboard only.

574073507_uwcant.png.f7faadcb759ac8dc8a4af904f2cd97eb.png1753657851_uwcantportonly.png.80fffa838006fbbb9f15e6e346d18625.png 121742769_uwcantstbonly.png.b8402fc4c9423150bc5202cf2c433b4c.png

So cant angle is sometimes 1 deg higher on starboard tack, but that could for other, tactical, reasons. I always thought LR was careful with what and when they reveal, so I wouldn't be completely surprised if they'd still be testing / holding back a foil upgrade for the AC if they make it. 

As for negative leeway, I think the gen 1 boats sailed like that a lot more than the gen 2 boats. "Crabbing windward" was one of the first debates here. In some videos it was very obvious. I think the sail plan would actually benefit from opening up the gap between the jib and main. However, the hull aero may suffer, especially with the more pronounced keels the gen 2 boats have. 

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10 hours ago, Mozzy Sails said:

 I can't really think of a reason why a team would want to be asymmetric like this. 

Perhaps having one foil that is better at take off means that they can always get up in light winds and then tack into the other foil.

The other way to think of it is that if you need to compromise foils for take off, then there is less need to compromise both.

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Perhaps, but, in reality, you never really get the choice of which foil you attempt to get re-airborne on. It's just pot luck of where you fall off on the course. 

The only time you do control which foil you attempt to get flying on is pre-start. And there they can get towed up. 

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On 2/16/2021 at 12:36 AM, erdb said:

Do you think LR may be running an asymmetric foil setup? It's either that or their compass is off a little.

I checked my code again, everything seems to be correct. Yes, I flip the tacks, so positive leeway always means the same ("sliding" to leeward relative to centerline).

Weirdly, this split with leeway between port vs starboard only happens with LR. My first reaction was that I surely screwed up something, but look at these graphs from "Race-19":

Upwind leeway both tacks, port only, starboard only:

625429360_uwleewboth.png.d44354a9c1c6452d0ca4f3e99b0476f1.png  1218783708_uwleewp.png.303a68a1be73fe596cd4e633d76ff9d5.png  1255428828_uwleewsb.png.fdcb0612b236e59ecfe31132ffa37605.png

Leeway is exactly the same for INEOS on both tacks. LR has the same +2 deg leeway on starboard, but -0.8 deg on port.

Looks similar downwind:

both tacks, port only, starboard only:

1735979706_dwleewboth.png.e6b0bf45404e2d08eb3d2e9da2911e2b.png  701478645_dwleewp.png.13b4c6bc1c36d3534a231d4299b5235b.png  740017487_dwleewsb.png.2966df01050c6d10b97d420a6bac5e86.png

On starboard, both INEOS and LR have positive leeway, although LR's angle is a little higher. On port, INEOS has pretty much the same leeway as on starboard, but once again LR has negative leeway on port (-1.2 deg).

I've checked all the other races for LR going back to RR3, and they always have negative leeway on port.

So it's either their compass is slightly off, and it hasn't been touched since RR3, or there is a slight difference between the two sides in foil to foil arm angle or a foil profile / flap shape. Or maybe it's JS vs Bruni!  One likes to pull the flap lever harder! :D

If LR really sailed with a different leeway on port & starboard, surely it would show in their sheeting angles on videos?

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@Basiliscus: Thank you for your superb analysis.

I have been thinking about how far these 2-dimensional flow codes such as Foil or MSES can take us, considering that turbulence is totally 3-dimensional by nature. How correctly can the 2-dimensional boundary layer theory describe the growth of the turbulent boundary layer, restricted in 2 dimensions?

I’m sure codes like Xfoil are geared towards 3-dimensional accuracy, since the results have been compared to wind tunnel tests, executed with very low aspect ratio wings, rather than really 2-dimensional “profiles”. With pressure tapping on the centre line of such a profile, you should get results encompassing 3-dimensional turbulence, within a 2-dimensional flow field.

It would be interesting to run a RANS (or LBM) code, with a 1 m wide profile spanning from wall to wall in a 3-dimensional domain, and compare that to results obtained in a 2-dimensional (RANS) model. I should do that with your beautiful H124 profile, as soon as I find the time :-)

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I think the 2D codes are pretty good, so long as the outer flow is 2D.  As I understand it, the Tollmien-Schlichting waves are pretty much 2D in the laminar boundary layer as they undergo linear amplification.  Once things get nonlinear and the boundary layer transitions to turbulent flow, then there are 3D structures like hairpin vortices in the boundary layer.  However the averaged mixing effect of these 3D structures is accounted for by the parameters of the integral boundary layer calculation.

It's when the outer flow is 3D that the integral boundary layer method starts to lose accuracy.  Spanwise pressure gradients and attachment line flows are not accounted for in the 2D calculation.  There is also the superposition of outer flows, such as at strut/bulb/wing junctions, that alters the local velocities from those calculated from the 2D shape.  

This large eddy simulation of an AC72 wingsail section done by Mario Caponetto is along the lines of what you propose.  It's a good reminder that what looks to be a nice smooth edge to the boundary layer in MSES or Xfoil is anything but in real life.

LES3final.thumb.PNG.de008fb4fababc3153dd2af1c743129a.PNG

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HI @Mozzy Sails, @MaxHugen, @dorox and @Basiliscus

Love the videos from @Mozzy Sails and the analysis from everyone else.  I'm in Australia and am doing a masters in naval engineering.  I've made a 6DoF VPP for the AC50 catamarans and AC75 monohulls using XFLR5 and MATLAB.  

@dorox how are you getting the raw data out of Virtual Eye? For AC35 I was able to get this data in a csv file. I've opened up developer tools in google chrome but can seem to find the link or file for the sources data.

@MaxHugen your drawing of the foils and line drawings from Chevalier have been great for having a starting point for foil and hull shapes. Are your profiles done in AutoCAD?

I see a lot of people are using XFLR5 and XFoiler. Are you using LLT or VLM2? I've done a comparison to tank testing for a moth T-foil (foil=NACA0012 and strut=NACA0015) and found lift is accurate to AOA=6deg for VLM2 and up to AOA=9deg for VLM2 with viscous drag underestimated.  Are you using any correction factor for form drag between the foil and struts?

Has anyone modelled the sails in XFLR5 or XFoiler?  what type of profile have you used? Below is screen shot of my Inventor models I was using to determine rough CoG and inertia values for a time domain VPP.

 

Cheers,

Neil

image.thumb.png.8bf9d126bb229882786031aac309c617.png

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On 2/16/2021 at 8:36 AM, erdb said:

Do you think LR may be running an asymmetric foil setup? It's either that or their compass is off a little.

I checked my code again, everything seems to be correct. Yes, I flip the tacks, so positive leeway always means the same ("sliding" to leeward relative to centerline).

Weirdly, this split with leeway between port vs starboard only happens with LR. My first reaction was that I surely screwed up something, but look at these graphs from "Race-19":

Upwind leeway both tacks, port only, starboard only:

625429360_uwleewboth.png.d44354a9c1c6452d0ca4f3e99b0476f1.png  1218783708_uwleewp.png.303a68a1be73fe596cd4e633d76ff9d5.png  1255428828_uwleewsb.png.fdcb0612b236e59ecfe31132ffa37605.png

Leeway is exactly the same for INEOS on both tacks. LR has the same +2 deg leeway on starboard, but -0.8 deg on port.

Looks similar downwind:

both tacks, port only, starboard only:

1735979706_dwleewboth.png.e6b0bf45404e2d08eb3d2e9da2911e2b.png  701478645_dwleewp.png.13b4c6bc1c36d3534a231d4299b5235b.png  740017487_dwleewsb.png.2966df01050c6d10b97d420a6bac5e86.png

On starboard, both INEOS and LR have positive leeway, although LR's angle is a little higher. On port, INEOS has pretty much the same leeway as on starboard, but once again LR has negative leeway on port (-1.2 deg).

I've checked all the other races for LR going back to RR3, and they always have negative leeway on port.

So it's either their compass is slightly off, and it hasn't been touched since RR3, or there is a slight difference between the two sides in foil to foil arm angle or a foil profile / flap shape. Or maybe it's JS vs Bruni!  One likes to pull the flap lever harder! :D

They might be pinching/footing differently between tacks. The course is never symmetric as the wind is never perfectly aligned with marks in direction nor the speed/gusts steady over the course, so they likely have different speed and pinching/footing requirements. Note in image below that they do have two bands of leeway, a 0deg and a 2 deg. So this may be down to the helmsman or tactician calling a mode based on where he wants to be on the course. Who's port helmsman?

625429360_uwleewboth.png.d44354a9c1c6452d0ca4f3e99b0476f1.png

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1 hour ago, TazLikesBoats said:

Has anyone modelled the sails in XFLR5 or XFoiler?  what type of profile have you used?

^ G'day Neil. I have profiles of the mainsail, headsail and foil which I use in XFLR5 for XFoil calcs.

The mainsail profile is derived from the mast profile (p37 of the Rules), and scaled for use with a sail chord of 7m (at the foot). The leeward skin profile is from a NACA generated shape, the windward skin is my interpretation.

image.png.d33233ccd8e9dc24ad6c5c91c4189097.png

image.png.be883b2ebc55b136124779809138e730.png

A headsail was difficult to use in XFoil (for convergence) without a suitable leading edge, so I ended up adapting the Eppler 376 as best I could.

For the foil I initially created a rough approximation from pics. Later I compared it to the NACA 64-206 foil, and found it was quite similar in profile, but increased the thickness to 9%. For calcs with flap, I use Flap Hinge at 60% from LE (as per NZ's foil).

Mainsail: AC75 8406.dat    (at 6% camber)
Headsail: EPPLER 376 (6403).dat
Foil: AC75 2509-00.dat     (from NACA 64-206)

Good luck with your calcs - look forward to seeing what you derive! :)

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18 minutes ago, Ncik said:

They might be pinching/footing differently between tacks. The course is never symmetric as the wind is never perfectly aligned with marks in direction nor the speed/gusts steady over the course, so they likely have different speed and pinching/footing requirements. Note in image below that they do have two bands of leeway, a 0deg and a 2 deg. So this may be down to the helmsman or tactician calling a mode based on where he wants to be on the course. Who's port helmsman?

625429360_uwleewboth.png.d44354a9c1c6452d0ca4f3e99b0476f1.png

It's possible, but it's suspicious that they have this double peak distribution both up- and downwind in all their races I analyzed since RR3. I don't have their GPS data from the earlier races. I think the most obvious answer is that the compass is off a little, but there are much more exciting - although less likely - explanations as well.

Port helmsman is Bruni.

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5 minutes ago, MaxHugen said:

^ G'day Neil. I have profiles of the mainsail, headsail and foil which I use in XFLR5 for XFoil calcs....

Good luck with your calcs - look forward to seeing what you derive! :)

Hi Max,

 

Thanks that is great! I want to stick to using an unmodified NACA series foil for the foils so that I can hopefully find some experimental data for comparison.  For the AC50 I stuck with using a NACA0012. A symmetrical foil is not as efficient as a foil with camber but meant I could compare with experimental data. for the AC75 I am looking at using an asymmetrical NACA foil ideally something where I can compare to a papers experimental data.

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14 minutes ago, TazLikesBoats said:

Hi Max,

 

Thanks that is great! I want to stick to using an unmodified NACA series foil for the foils so that I can hopefully find some experimental data for comparison.  For the AC50 I stuck with using a NACA0012. A symmetrical foil is not as efficient as a foil with camber but meant I could compare with experimental data. for the AC75 I am looking at using an asymmetrical NACA foil ideally something where I can compare to a papers experimental data.

Understand. You might find Eppler's paper on hydrofoils useful?

He discusses the NACA 64-206 foil as well as others:

Eppler - Section_Design_for_Hydrofoil_Wings_with_Flaps.pdf

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9 hours ago, TazLikesBoats said:

Has anyone modelled the sails in XFLR5 or XFoiler?  what type of profile have you used? Below is screen shot of my Inventor models I was using to determine rough CoG and inertia values for a time domain VPP.

For what it's worth, I can give the sail shapes I've used so far - don't know how useful they are, since each skin is a separate sail & the mast is separate, too. One simple and free tool that could be useful for simulating the sails (and the foils) is MachUp, at http://aero.go.usu.edu/mu4/

LR1.png

LR2.png

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On 2/15/2021 at 2:36 PM, erdb said:

Do you think LR may be running an asymmetric foil setup? It's either that or their compass is off a little.

I checked my code again, everything seems to be correct. Yes, I flip the tacks, so positive leeway always means the same ("sliding" to leeward relative to centerline).

Weirdly, this split with leeway between port vs starboard only happens with LR. My first reaction was that I surely screwed up something, but look at these graphs from "Race-19":

Upwind leeway both tacks, port only, starboard only:

625429360_uwleewboth.png.d44354a9c1c6452d0ca4f3e99b0476f1.png  1218783708_uwleewp.png.303a68a1be73fe596cd4e633d76ff9d5.png  1255428828_uwleewsb.png.fdcb0612b236e59ecfe31132ffa37605.png

Leeway is exactly the same for INEOS on both tacks. LR has the same +2 deg leeway on starboard, but -0.8 deg on port.

Looks similar downwind:

both tacks, port only, starboard only:

1735979706_dwleewboth.png.e6b0bf45404e2d08eb3d2e9da2911e2b.png  701478645_dwleewp.png.13b4c6bc1c36d3534a231d4299b5235b.png  740017487_dwleewsb.png.2966df01050c6d10b97d420a6bac5e86.png

On starboard, both INEOS and LR have positive leeway, although LR's angle is a little higher. On port, INEOS has pretty much the same leeway as on starboard, but once again LR has negative leeway on port (-1.2 deg).

I've checked all the other races for LR going back to RR3, and they always have negative leeway on port.

So it's either their compass is slightly off, and it hasn't been touched since RR3, or there is a slight difference between the two sides in foil to foil arm angle or a foil profile / flap shape. Or maybe it's JS vs Bruni!  One likes to pull the flap lever harder! :D

Truly brilliant, thank you so much for all of this 

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2 hours ago, Stingray~ said:

Truly brilliant, thank you so much for all of this 

Hi @erdb,

How are you getting the data? Do you have it in a csv file?  Would be great to compare with my VPP. Any help would be greatly appreciated

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I tried to make a screenshot, but a still picture doesn't show anything convincing, but when on the 5th leg, LR is 1300 - 1400m from the upwind mark, the chopper flies behind them while they're on port. To me they really seem to be crabbing to windward = negative leeway. Maybe the data is good, and they do have an asymmetric setup for some reason.

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1 minute ago, Mozzy Sails said:

@MaxHugen did you ever do a projection drawing of the new ETNZ foils and LR foils? For shape and area?

No, haven't been able to get any decent close up pics, at the right angles, to do them.

Have done some comparisons using poor quality long distance pics, and can't see a significant difference in area though.

Only minor changes observed in the planforms, such as slightly thinner tips on NZ's latest foils, and slightly straighter leading edges on LR's.

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38 minutes ago, MaxHugen said:

No, haven't been able to get any decent close up pics, at the right angles, to do them.

Have done some comparisons using poor quality long distance pics, and can't see a significant difference in area though.

Only minor changes observed in the planforms, such as slightly thinner tips on NZ's latest foils, and slightly straighter leading edges on LR's.

What did you think of NO's comments about NZ's foils being 30% smaller than LRPPs? 

Sound correct to your expert eye? 

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2 minutes ago, 45Roller said:

What did you think of NO's comments about NZ's foils being 30% smaller than LRPPs? 

Sound correct to your expert eye? 

"Expert" might be pushing it... but my measurements indicate that NZ's foils are about 35% smaller:

image.png.7cbde510dcfaf360ff7891ab83e4d895.png

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3 minutes ago, MaxHugen said:

"Expert" might be pushing it... but my measurements indicate that NZ's foils are about 35% smaller:

image.png.7cbde510dcfaf360ff7891ab83e4d895.png

Ok can you ELI5 to me why that's an advantage, and what are the possible disadvantages to them going with a much smaller foil? 

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3 minutes ago, 45Roller said:

Ok can you ELI5 to me why that's an advantage, and what are the possible disadvantages to them going with a much smaller foil? 

All things being equal*, small foil will need more takeoff speed, say 19kts boatspeed rather than 17kt. Will be draggier in the high and slow mode that LR did so well, beacuse you are off optimal ~ 4 deg aoa situation because your increase in induced drag is outweighing the wetted surface improvement.

That said it''ll be dynamite once you are going over 30 - 35kts.

*They may have done something with section design or flaps which means that they can get same grunt from smaller area, oooor they could have some rig benefit that means they have enough low end punch  to unstick the foils at lower speeds.

Who knows, will be bloody interesting

 

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1 hour ago, Daniel Holman said:

All things being equal*, small foil will need more takeoff speed, say 19kts boatspeed rather than 17kt. Will be draggier in the high and slow mode that LR did so well, beacuse you are off optimal ~ 4 deg aoa situation because your increase in induced drag is outweighing the wetted surface improvement.

That said it''ll be dynamite once you are going over 30 - 35kts.

*They may have done something with section design or flaps which means that they can get same grunt from smaller area, oooor they could have some rig benefit that means they have enough low end punch  to unstick the foils at lower speeds.

Who knows, will be bloody interesting

 

With LR having such a high mode I suspect they are different tab angles for the inner and outer section of the foil.  This means they can produce a lot of leeway force quickly to have the high mode while maintaining a more consistent lift force. It will be interesting to see if ETNZ can do the same thing with their foils as it looks like they have one foil tab angle for the whole foil.

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24 minutes ago, TazLikesBoats said:

With LR having such a high mode I suspect they are different tab angles for the inner and outer section of the foil.  This means they can produce a lot of leeway force quickly to have the high mode while maintaining a more consistent lift force. It will be interesting to see if ETNZ can do the same thing with their foils as it looks like they have one foil tab angle for the whole foil.

Not sure that is permitted under the rules?

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1 minute ago, southseasbill said:

Not sure that is permitted under the rules?

There is nothing in the rules to stop it. Yes the foils have to be symmetrical about the centre but nothing stopping you from having different control on each side.  It wasn't my idea Nathan Outteridge said it back at the Christmas Cup

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21 minutes ago, Daniel Holman said:

*They may have done something with section design or flaps which means that they can get same grunt from smaller area, oooor they could have some rig benefit that means they have enough low end punch  to unstick the foils at lower speeds.

In all likelihood ETNZ has both between the seamless single alerion and increased sail power from their boomless main extension. Some of the recent footage of them in the light stuff seems to me to support the idea that they're just making way more lift than the other boats with less foil area. 

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4 hours ago, Wild Things said:

In all likelihood ETNZ has both between the seamless single alerion and increased sail power from their boomless main extension. Some of the recent footage of them in the light stuff seems to me to support the idea that they're just making way more lift than the other boats with less foil area. 

More power with less drag. Pretty powerful combination :ph34r:

Going off the time stamps of the footage of ETNZ training after the final race verse LR in the final race. ETNZ were 20 seconds faster during their practice upwind after the final race than LR were on their last upwind of the final race.

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6 hours ago, MaxHugen said:

"Expert" might be pushing it... but my measurements indicate that NZ's foils are about 35% smaller:

image.png.7cbde510dcfaf360ff7891ab83e4d895.png

NO was probably referring to THIS drawing of Max's, truth be told. ;-)

Edited by Sailbydate
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5 hours ago, TazLikesBoats said:

With LR having such a high mode I suspect they are different tab angles for the inner and outer section of the foil.  This means they can produce a lot of leeway force quickly to have the high mode while maintaining a more consistent lift force. It will be interesting to see if ETNZ can do the same thing with their foils as it looks like they have one foil tab angle for the whole foil.

The benefit of that is they can have smaller foils which they have taken well advantage of with their foils being about 30% smaller.

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3 hours ago, uflux said:

Going off the time stamps of the footage of ETNZ training after the final race verse LR in the final race. ETNZ were 20 seconds faster during their practice upwind after the final race than LR were on their last upwind of the final race.

Interesting.

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3 hours ago, uflux said:

More power with less drag. Pretty powerful combination :ph34r:

Going off the time stamps of the footage of ETNZ training after the final race verse LR in the final race. ETNZ were 20 seconds faster during their practice upwind after the final race than LR were on their last upwind of the final race.

So we're sandbagging then? ;)

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5 hours ago, uflux said:

More power with less drag. Pretty powerful combination :ph34r:

Going off the time stamps of the footage of ETNZ training after the final race verse LR in the final race. ETNZ were 20 seconds faster during their practice upwind after the final race than LR were on their last upwind of the final race.

LR were likely cruising home with a 700m+ lead by that point?

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10 minutes ago, arneelof said:

 

If that really holds up - we will have a short and not very exciting cup.

 

I'm not saying that ETNZ had chucked the sand overboard either. We'll not know until the 6th. Fun, eh?

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30 minutes ago, Nutta said:

LR were likely cruising home with a 700m+ lead by that point?

I doubt it...they would want to make sure of the victory. 

They were also 30 seconds slower in comparison downwind. So almost a minute slower over a lap.

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WARNING: NERD ALERT!
Easy to follow explanation of velocity and pressure when trying to understand Bernoulli's Principle:

 

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12 hours ago, I ride bikes said:

Is it permissible to twist the foils?

Isn’t it more difficult to make them so they don’t twist?

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20 hours ago, Daniel Holman said:

All things being equal*, small foil will need more takeoff speed, say 19kts boatspeed rather than 17kt. Will be draggier in the high and slow mode that LR did so well, beacuse you are off optimal ~ 4 deg aoa situation because your increase in induced drag is outweighing the wetted surface improvement.

That said it''ll be dynamite once you are going over 30 - 35kts.

*They may have done something with section design or flaps which means that they can get same grunt from smaller area, oooor they could have some rig benefit that means they have enough low end punch  to unstick the foils at lower speeds.

Who knows, will be bloody interesting

 

AR does have aoa l/d & reattached flow implications, so control input may be different, faster, and more precise for NZ.  It would need to be.  LR planform, at least,  looks to be more forgiving, which might explain their advantage maneuvering, in crappy tactical positions, being covered, and even sometimes in bigger waves, both upwind and down. 

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23 minutes ago, Amati said:

AR does have aoa l/d & reattached flow implications, so control input may be different, faster, and more precise for NZ.  It would need to be.  LR planform, at least,  looks to be more forgiving, which might explain their advantage maneuvering, in crappy tactical positions, being covered, and even sometimes in bigger waves, both upwind and down. 

I haven't seen any evidence to suggest that the larger foils will take-off at lower speeds. In one race both GB and AM both took off, after coming off the foils, at ~18.8 knots (if speeds were anywhere near accurate in the video).

For take-off, NZ needs to increase flap angle more than GB or LR to get equivalent lift force, but some calcs indicate that NZ's narrow foils still have a better L/D ratio than the wider ones. NZ takes off with zero pitch, using their narrow canoe-shaped bustle to effectively help reduce wetted area.

As discussed, I'd assume that these narrow foils are less forgiving than the wider foils, but it appears that NZ has both the experience and well-designed flight controllers to manage them.

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2 hours ago, MaxHugen said:

WARNING: NERD ALERT!
Easy to follow explanation of velocity and pressure when trying to understand Bernoulli's Principle:

 

Thanks for this one Max, very informative B)

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Bas,

    Thanks for your explanations here. Are you involved with Paul Bieker on the foiling ferryboat? 

    The earlier foil section you started with here before modding for the flaps looked somehow familiar to me and I looked up the foil that my sailplane uses, 

Wortmann FX-60-157

    I always thought it seemed fat but I guess it is somewhat laminar flow and seems to do the job.

http://airfoiltools.com/airfoil/details?airfoil=fx60157-il

    image.png.f14a109f4f18ed33e994e57f2794e67c.png

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1 hour ago, MaxHugen said:

I haven't seen any evidence to suggest that the larger foils will take-off at lower speeds. In one race both GB and AM both took off, after coming off the foils, at ~18.8 knots (if speeds were anywhere near accurate in the video).

For take-off, NZ needs to increase flap angle more than GB or LR to get equivalent lift force, but some calcs indicate that NZ's narrow foils still have a better L/D ratio than the wider ones. NZ takes off with zero pitch, using their narrow canoe-shaped bustle to effectively help reduce wetted area.

As discussed, I'd assume that these narrow foils are less forgiving than the wider foils, but it appears that NZ has both the experience and well-designed flight controllers to manage them.

Pressure under the larger LR foils (I know :o) at low speeds might make up some for a better but possibly lower d/l for a lower AR foil?  Reynold’s number might come into play here as far as flow reattachment too.  So hull design for non foiling speeds, specifically low WS and prismatic, might be optimized for LR to accelerate more quickly up to lower flying speed, even at semi planing speeds, specifically to match low speed foil dynamics?

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1 hour ago, MaxHugen said:

I haven't seen any evidence to suggest that the larger foils will take-off at lower speeds. In one race both GB and AM both took off, after coming off the foils, at ~18.8 knots (if speeds were anywhere near accurate in the video).

For take-off, NZ needs to increase flap angle more than GB or LR to get equivalent lift force, but some calcs indicate that NZ's narrow foils still have a better L/D ratio than the wider ones. NZ takes off with zero pitch, using their narrow canoe-shaped bustle to effectively help reduce wetted area.

As discussed, I'd assume that these narrow foils are less forgiving than the wider foils, but it appears that NZ has both the experience and well-designed flight controllers to manage them.

Foils work harder at lower speeds so for daggerboards at least, bigger is better to certain point, or refinement, at least, given equal spans and sails.  (One thing I learned messing around with div 2 boards).  Flapped foils, though.....:)

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2 hours ago, Amati said:

Isn’t it more difficult to make them so they don’t twist?

Sort of. I accidentally made a gybeing dagger system that I became convinced twisted shut. Constrained in all planes at deck, but only at the TE at the exit of the hull, so without infinite torsional stiffness I think it did the opposite of twist up when loaded.

This will also happen passively with forward rake, and twisting open will happen passively with aft rake / sweep.

 

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