Tornado-Cat

The winning foils

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^ Exactly how I see it as well TC.

 

To see how the AOA on the horizontal foil changes during heave, you must see that as the boat rises it also moves to leeward (according to Tom Speer, anyway). If a line could be drawn from any point on the horizontal foil just prior to heave commencing, and terminating the line at maximum heave (and leeway) then the line will be on a diagonal rather than just vertical (I'm ignoring the forward distance-covered vector of this line). As the foil moves along this line it will "see" a change in AOA that will be reduced, and thus reduce lift, and the greatest change in AOA will be seen by a foil that has a span more perpendicular to this line.

 

In an ideal world where heave is not present then the most efficient dihedral angle for the horizontal foil is actually zero or close to it, and this may explain why some of the foils we see have a larger horizontal portion in proportion to the greater diherdal portion

 

By combining low and high dihedral then the foil can function not only as an efficient load-carrying foil, but can also respond to heave/leeway changes.

 

I'm certainly not saying any of this is correct and it probably isn't, but in my mind I can see how this scenario could work and explain what we see.

 

EDIT: Damn. Once again I withdrew my post to add to it while TC added his. This should have been just before TC's post above, and it looks like we have both reached very similar conclusions.

Edited by Count Drac

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^ Exactly how I see it as well TC.

 

To see how the AOA on the horizontal foil changes during heave, you must see that as the boat rises it also moves to leeward (according to Tom Speer, anyway). If a line could be drawn from any point on the horizontal foil just prior to heave commencing, and terminating the line at maximum heave (and leeway) then the line will be on a diagonal rather than just vertical (I'm ignoring the forward distance-covered vector of this line). As the foil moves along this line it will "see" a change in AOA that will be reduced, and thus reduce lift, and the greatest change in AOA will be seen by a foil that has a span more perpendicular to this line.

 

In an ideal world where heave is not present then the most efficient dihedral angle for the horizontal foil is actually zero or close to it, and this may explain why some of the foils we see have a larger horizontal portion in proportion to the greater diherdal portion

 

By combining low and high dihedral then the foil can function not only as an efficient load-carrying foil, but can also respond to heave/leeway changes.

 

I'm certainly not saying any of this is correct and it probably isn't, but in my mind I can see how this scenario could work and explain what we see.

 

EDIT: Damn. Once again I withdrew my post to add to it while TC added his. This should have been just before TC's post above, and it looks like we have both reached very similar conclusions.

^ Correct !

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Bar now has at least two different UptiP foils: (Top photo posted by nav and cropped here, bottom photo posted by nav on p4 with no other photo credits)

 

1nxnwp.jpg

 

20jsaqv.jpg

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Here is a "definition" for those that don't know or can't tell an UptiP foil when they see one:

 

definition(to be applied using a picture of a deployed foil) : any foil that when it is deployed allows the more or less horizontal portion to be less than 90 degrees from a line normal(90 degrees) to the waters surface and/or when the more or less horizontal portion is less than 90 degrees from the more or less vertical portion of the foil as in the sketch:

stb hull coming at you:

post-30-0-92424400-1467666477_thumb.png

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Doug, you owe me a new keyboard! I couldn’t have hoped for nor expected such a fantastically predictable response to my post........ It’s true what they say – It is good to belly laugh.

Following my post, biplane boy's response is to post the attached thumbnail of the original ETNZ uptip foil.

A style of board that is no longer seen, deployed in a manner also no longer seen.
Why? - Because they are a (relatively) high drag, low RM solution that is suited to downwind applications.

I wrote: Yes, fundamentals remain analogous - but the relationship between flight, height of flight and leeway resistance is no longer driven by the early leeway coupling principle that you continually refer to.

I don't dispute that there is still an intrinsic relationship between vertical and horizontal foil elements that combine to control height and leeway in a symbiotic manner.

The original uptips required a very similar level of dihedral between the two elements to achieve the auto height stabilisation which was enabled by leeward slip.

Even TC wrote in post #405:
1) It is the coupling of leeway with heave that is exploited by the L foil to provide vertical static stability.

However, what is being forgotten here is that the current cycle is foiling everywhere – not just downwind – and the more efficient way to proceed upwind is to eliminate leeway wherever possible or at least minimise it as much as practically possible.

What was radical with the AC72’s is now widely copied on one designs – by they GC32’s or Flying Phantoms. Cool? Yes! Cutting Edge? No. The game has moved on a long way from those AC34 days. So to see endless and predictable rehashing of first generation foil technology by the florida biplane boy is misleading as to what is going on NOW.

I wrote in post #312 how that all foils will have two elements at approximately 90 degress – but this does not make them uptip – that whole term is reundundant and misleading – hence our endless calls for the foils to be described as T , L or Tick. They are descriptives only – definition is unnecessary and misleading when used in the context applied by Doug.

(View attached Dagram: Contemporary AC foil - Not uptip)

Which if you them simplify to Doug’s original pictograms gives you:

(View attached Diagram: Does Not equal)

This is why I have consistently stated that the uptip mechanism as stated by Speer is no longer in play and why uptip is redundant as a phrase. There is no automatic heave stability when deployed in this manner.

It does not require a large step to see how the diagram on the above left could be a Moth Hull with T shaped main foil – but missing the leeward lower horizontal (Turning a T to an L) and with the boat only just entering into Veal Heel Mode.

I am not saying that it is Veal Heel – but for those that understand the virtuous cycle that Veal Heel brings about would also understand the parallels that AC designers would be trying to assimilate – it just requires some very complex engineering, control systems and massive cost – perfect design storm for AC boffins to try and resolve.

Slag me as much you like – it is water off a ducks back – but facts are facts – the game is very different now.

Re read posts 312, 333, 368, 380 and 395

post-108539-0-11608800-1467693481_thumb.png

post-108539-0-40881400-1467693503_thumb.png

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Boink, a good summary of where we are at now, I think.

 

From what I see of the modern foil photos, most if not all still have a certain amount of positive dihedral when the foil is fully employed as deep as it can go. I believe this is a consequence of the heave/leeway motion of the boats and is the obvious way to employ some form of auto-correcting (assuming the conclusions Tornado-Cat and I have come to are correct). The foils can have any combination of constant dihedral along the whole horizontal span, which may make building them easier, to a combination of dihedral angles (which may even be influenced by how tightly they can be tucked up against the windward hull). As TC said above - the computers will be working overtime to come up with the best configurations.

 

I also agree that the surface-piercing foils we saw in the previous cup are far less efficient compared to keeping the foil submerged all the time, and were probably the best solution to maintaining ride-height in the absence of really good and quick foil control systems.

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Doug, you owe me a new keyboard! I couldn’t have hoped for nor expected such a fantastically predictable response to my post........ It’s true what they say – It is good to belly laugh.

 

Following my post, biplane boy's response is to post the attached thumbnail of the original ETNZ uptip foil.

 

A style of board that is no longer seen, deployed in a manner also no longer seen.

Why? - Because they are a (relatively) high drag, low RM solution that is suited to downwind applications.

 

I wrote: Yes, fundamentals remain analogous - but the relationship between flight, height of flight and leeway resistance is no longer driven by the early leeway coupling principle that you continually refer to.

 

I don't dispute that there is still an intrinsic relationship between vertical and horizontal foil elements that combine to control height and leeway in a symbiotic manner.

 

The original uptips required a very similar level of dihedral between the two elements to achieve the auto height stabilisation which was enabled by leeward slip.

 

Even TC wrote in post #405:

1) It is the coupling of leeway with heave that is exploited by the L foil to provide vertical static stability.

 

However, what is being forgotten here is that the current cycle is foiling everywhere – not just downwind – and the more efficient way to proceed upwind is to eliminate leeway wherever possible or at least minimise it as much as practically possible.

 

What was radical with the AC72’s is now widely copied on one designs – by they GC32’s or Flying Phantoms. Cool? Yes! Cutting Edge? No. The game has moved on a long way from those AC34 days. So to see endless and predictable rehashing of first generation foil technology by the florida biplane boy is misleading as to what is going on NOW.

 

I wrote in post #312 how that all foils will have two elements at approximately 90 degress – but this does not make them uptip – that whole term is reundundant and misleading – hence our endless calls for the foils to be described as T , L or Tick. They are descriptives only – definition is unnecessary and misleading when used in the context applied by Doug.

 

(View attached Dagram: Contemporary AC foil - Not uptip)

 

Which if you them simplify to Doug’s original pictograms gives you:

 

(View attached Diagram: Does Not equal)

 

This is why I have consistently stated that the uptip mechanism as stated by Speer is no longer in play and why uptip is redundant as a phrase. There is no automatic heave stability when deployed in this manner.

 

It does not require a large step to see how the diagram on the above left could be a Moth Hull with T shaped main foil – but missing the leeward lower horizontal (Turning a T to an L) and with the boat only just entering into Veal Heel Mode.

 

I am not saying that it is Veal Heel – but for those that understand the virtuous cycle that Veal Heel brings about would also understand the parallels that AC designers would be trying to assimilate – it just requires some very complex engineering, control systems and massive cost – perfect design storm for AC boffins to try and resolve.

 

Slag me as much you like – it is water off a ducks back – but facts are facts – the game is very different now.

 

Re read posts 312, 333, 368, 380 and 395

 

Inaccurate, overly simplistic, nonsense that ignores the fact that most of the boats are using uptip foils! And that upwind AC foiling made its debut in 34!! Your "facts" are made up suppositions that are just plain wrong.

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Bar now has at least two different UptiP foils: (Top photo posted by nav and cropped here, bottom photo posted by nav on p4 with no other photo credits)

 

1nxnwp.jpg

 

20jsaqv.jpg

 

The foils above when fully deployed behave as UptiP foils relying on leeway coupling for lift control without relying on the surface piercing tip on some uptip foils. As such they meet the low drag criteria mentioned by Tom Speer below. The shape of the board allows the lifting surface to move outboard slightly increasing the righting arm and therefore righting moment.

It should be clear that an UptiP foil doesn't have to look like the original TNZ foil to provide automatic lift control-there is a wide range of shapes that work the same way. It should also be clear that the critical design element is to provide a low drag foil that is also heave stable in order to reduce ,as much as possible, the workload on the control system and the person operating it. Automatic electronic foil control is illegal so what the designers are doing is improving the response time and accuracy of foil rake adjustment. But that has to be mated with a foil that provides the highest level of intrinsic ride height control(heave stability) with the lowest level of drag possible.

========

 

Tom Speer's rather detailed explanation of how an UptiP foil works. Some uptip foils work a bit differently than what he describes because the foil designer wanted the tip to behave like a surface piercing foil.(GC32)

But nonetheless an excellent technical description:

The curved part of the vertical foil produces essentially the same lift as it rises. This is necessary to counter the side force from the sail rig, which does not change as the height changes.

 

Because the horizontal lift is constant but the vertical area is reduced as the boat rises, the leeway angle increases. It is the coupling of leeway with heave that is exploited by the L foil to provide vertical static stability.

 

The dihedral angle of the horizontal wing is set so that the angle of attack of the wing is reduced as the leeway angle increases. This satisfies the static stability condition that the vertical lift decrease as the heave increases.

 

Because the same horizontal lift is produced over a reduced vertical span, the sideways wash in the wake is also greater and the trailing vortices are more intense. This causes a coupling with the horizontal wing that increases the vertical lift, because the horizontal wing acts as a winglet for the vertical part of the foil (and vice versa). The dihedral angle required for vertical stability is greater than what one might expect by looking at the wing alone because it must overcome this wake-coupled influence. The result is there is a range of dihedral angles that provide positive vertical stability and a range of dihedral angles that are destabilizing in heave because of the coupling with the shed vorticity of the vertical part of the foil.

 

Although there are times when the foil tip has broached the surface, this is not the normal mechanism for providing heave stability in L foils. The best performance is obtained with the hull just above the wavetops and the wing submerged well below the surface. The leeway-modulated heave stability is still effective in this condition, and the induced drag is minimized.

 

Canting the foil inboard has the effect of increasing the dihedral angle of the wing, which enhances the heave stability. The vertical lift is spread over a greater span because the curved part of the foil is oriented to provide more vertical component of the force. This reduces the induced drag due to the vertical force. However, the induced drag of the horizontal force would be increased, so cant is typically used off the wind when the side force from the rig is less and the side force produced by the foils is correspondingly less. The foils still have to support the weight of the boat, so the vertical force is not lessened, but the relative proportions of vertical and horizontal force are changed, making the canted foil better suited to the operating condition. Cant allows the leeway-modulated heave stability to be increased an an acceptable penalty in the induced drag because of the lower side force and the higher speeds, which also reduce induced drag.

 

Upwind, the foils are canted to their vertical position to minimize the induced drag from the high side force and reduced speeds. The reduction in horizontal wing dihedral angle with vertical cant impacts the leeway-modulated heave stability, which is why it is much more difficult to achieve stable flight upwind than downwind. The crew had to be more active in trimming the wing and foil to deal with the reduction in natural heave stability, which was very hard on the grinders when flyng upwind.

 

Whether canted or upright, the mechanism for providing natural heave stability was still the coupling between heave and leeway,(emphasis DL) which led to a reduction in vertical lift because of the designed-in coupling between leeway and vertical lift by virtue of the wing dihedral. Reduction in horizontal/vertical-lifting area due to the foil tip broaching the surface was not part of this primary source of heave stability. Allowing the tip to broach the surface had big penalties in terms of induced drag and increased leeway due to insufficient vertical span.

__________________

Tom Speer

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board.

 

Makes sense to me for the windward foil - not so much for the leeward.

 

Boat lifts - leeway increases - windward board "digs in" but doesn't leeward keep lifting (in a non-virtuous cycle)? Understood: when the lifting surface breaks the surface, then lift will be reduced (heave stability). But - before the lifting surface physically airs out - what is the effect of leeway on the leeward board?

 

post-18173-0-86855900-1467783788_thumb.jpg

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Please all of you just shut the fuck up.

 

I fear you are all inexplicably confused this shit is beyond boring.

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How to pump an hydro foll. Superb video, love the music (The Day - Moby).

I did not see that coming. :blink:

 

Thanks!

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board.

 

Makes sense to me for the windward foil - not so much for the leeward.

 

Boat lifts - leeway increases - windward board "digs in" but doesn't leeward keep lifting (in a non-virtuous cycle)? Understood: when the lifting surface breaks the surface, then lift will be reduced (heave stability). But - before the lifting surface physically airs out - what is the effect of leeway on the leeward board?

 

attachicon.gifimage.jpg

If this is true, it should work like the other uptip foils: when the foil is up it should increase the leeway, thus increasing the turbulence under the foil, thus decreasing the lift = autostable.

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board.

 

Makes sense to me for the windward foil - not so much for the leeward.

 

Boat lifts - leeway increases - windward board "digs in" but doesn't leeward keep lifting (in a non-virtuous cycle)? Understood: when the lifting surface breaks the surface, then lift will be reduced (heave stability). But - before the lifting surface physically airs out - what is the effect of leeway on the leeward board?

 

attachicon.gifimage.jpg

 

I found this description by Ferdinand Van West in catsailingnews.com:

 

Van West was asked by CSN(Martin) "Will the 4 foil setup will equal or better 3 foil NACRA 20FCS set up?"

 

We believe so, by designing the boards such that there is a leeway-coupling effect between the two surface piercing daggerboards, this effect together with the fluctuating surface area of the foil effected by the flight height makes the boat 'Heave Stable'.

 

------------------

Of course, this configuration is illegal on the AC boats...........

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board.

 

Makes sense to me for the windward foil - not so much for the leeward.

 

Boat lifts - leeway increases - windward board "digs in" but doesn't leeward keep lifting (in a non-virtuous cycle)? Understood: when the lifting surface breaks the surface, then lift will be reduced (heave stability). But - before the lifting surface physically airs out - what is the effect of leeway on the leeward board?

 

attachicon.gifimage.jpg

If this is true, it should work like the other uptip foils: when the foil is up it should increase the leeway, thus increasing the turbulence under the foil, thus decreasing the lift = autostable.
I guess "turbulence" under the leeward foil could be a factor. Not a very satisfying answer. Simple loss of lifting area might be the reality.

 

But that's part of the problem with understanding the dihedral foil - leeway induced change in aoa works for the "up half" of the dihedral.

 

Not so much for the "down half".

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Of course, this configuration is illegal on the AC boats...........

 

 

:lol::lol:

 

Carry on...

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board.

 

Makes sense to me for the windward foil - not so much for the leeward.

 

Boat lifts - leeway increases - windward board "digs in" but doesn't leeward keep lifting (in a non-virtuous cycle)? Understood: when the lifting surface breaks the surface, then lift will be reduced (heave stability). But - before the lifting surface physically airs out - what is the effect of leeway on the leeward board?

 

attachicon.gifimage.jpg

If this is true, it should work like the other uptip foils: when the foil is up it should increase the leeway, thus increasing the turbulence under the foil, thus decreasing the lift = autostable.
I guess "turbulence" under the leeward foil could be a factor. Not a very satisfying answer. Simple loss of lifting area might be the reality.

 

But that's part of the problem with understanding the dihedral foil - leeway induced change in aoa works for the "up half" of the dihedral.

 

Not so much for the "down half".

 

Dihedral: if the boat slips on the side the AOA will be sligthly modified, however I don't think it is so much the AOA than the turbulence that will affect the lift of the foil (personnal opinion though)

For the Z foil, the same process may occur but I would say that the lesser portion of the foil in the water has more importance and does not have the adverse side effect of an uptip piercing the surface.

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TC-a "Z" foil is a surface piercing foil.........see post 421.

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TC-a "Z" foil is a surface piercing foil.........see post 421.

Yes, I know. I don't think it has the same side effect as when the tip of an L uptip pierces the surface.

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How to pump an hydro foll. Superb video, love the music (The Day - Moby).

I did not see that coming. :blink:

 

Thanks!

 

Wish I was 40 years younger !!!

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board.

 

Makes sense to me for the windward foil - not so much for the leeward.

 

Boat lifts - leeway increases - windward board "digs in" but doesn't leeward keep lifting (in a non-virtuous cycle)? Understood: when the lifting surface breaks the surface, then lift will be reduced (heave stability). But - before the lifting surface physically airs out - what is the effect of leeway on the leeward board?

 

attachicon.gifimage.jpg

 

I found this description by Ferdinand Van West in catsailingnews.com:

 

Van West was asked by CSN(Martin) "Will the 4 foil setup will equal or better 3 foil NACRA 20FCS set up?"

 

We believe so, by designing the boards such that there is a leeway-coupling effect between the two surface piercing daggerboards, this effect together with the fluctuating surface area of the foil effected by the flight height makes the boat 'Heave Stable'.

 

------------------

Of course, this configuration is illegal on the AC boats...........

 

We wouldn't want poor old Oracle getting blindsided again so no wonder.

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Poke their eyes out I say...

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Van West was asked by CSN(Martin) "Will the 4 foil setup will equal or better 3 foil NACRA 20FCS set up?"

 

We believe so, by designing the boards such that there is a leeway-coupling effect between the two surface piercing daggerboards, this effect together with the fluctuating surface area of the foil effected by the flight height makes the boat 'Heave Stable'.

 

------------------

Of course, this configuration is illegal on the AC boats...........

 

 

We wouldn't want poor old Oracle getting blindsided again so no wonder.

 

 

It's not illegal though - just another DL 'misunderstanding'......

 

4509206-md-510x371.jpg

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Haven't followed this shitfight to much, but wouldn't have worked in the last one as you were only allowed 2 foils down for a short time.

 

Has this time restraint been removed for this version.

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Haven't followed this shitfight to much, but wouldn't have worked in the last one as you were only allowed 2 foils down for a short time.

 

Has this time restraint been removed for this version.

Yes

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You simple creature, I attach a labelled diagram to explain to you why configuration and orientation of similar foil shapes WILL give different outcomes to heave stability and ride height. ETNZ style foils were proportional in how they generated lift and traded that lift with reduced leeway resistance in a predictable and controllable manner. But when these foils are set vertically or canted outward - that proportional relationship is lost and either higher level foil control is required OR you resort to the Lurching Hip Hop style of flight control that you yourself, are all too familiar with.....

 

I have consistently said that the new orientation and configuration are only possible because of the higher level of foil control that is available now, and this includes active Rudder control. I have also consistently said that there are a lot of parallels between foils from last to current cup cycle - but all of this reinforces why foils with 90 turns should not be labelled uptip (try T, L or Tick) and why it is misleading.

 

All of this would also explain why, how without such refined foil control and not previously being allowed to have active rudder control, that Foil shapes as shown in Post #329 were not flight stable to the extent that ETNZ had flight stability.......)

 

Flame on biplane boy. Cant wait for the red ink and indignation. I have fresh popcorn kernels ready for the weekend.......

 

 

post-108539-0-05492400-1467980514_thumb.png

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Haven't followed this shitfight to much, but wouldn't have worked in the last one as you were only allowed 2 foils down for a short time.

 

Has this time restraint been removed for this version.

Yes

 

 

No.

 

The question is false - because you were allowed two foils down last time - as you are this time.

 

The significant wording has not changed, i.e.

 

11.14 Daggerboards shall not be used to generate force for the purpose or effect of increasing righting moment when used on the windward side of an AC Class

Yacht.

 

(a few of the details of when this does not apply - have been changed however)

 

 

So using a foil to lift the windward hull was and remains ok* '4x4oiling'

 

 

*but note: having the ww board down and that hull not lifted - might leave you open to protest and needing to prove the board was not increasing RM

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The blind leading the blind here.

 

Boink and doug. Give it a rest!... supposition is not you strong points dudes.

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Are there any rules to prevent foils from actively (de)forming to 'flap their wings' for adding power, stingray-style?

I would say that actively yes, passively no.

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Are there any rules to prevent foils from actively (de)forming to 'flap their wings' for adding power, stingray-style?

I would say that actively yes, passively no.
Yes, rules prevent it from being done actively?

 

Passively, I wonder if there is energy that can be captured and redirected from wave or other gravity-induced fluctuations.

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Are there any rules to prevent foils from actively (de)forming to 'flap their wings' for adding power, stingray-style?

I would say that actively yes, passively no.
Yes, rules prevent it from being done actively?

 

Passively, I wonder if there is energy that can be captured and redirected from wave or other gravity-induced fluctuations.

 

11.11 specifies that the "dagger board shape shall not be adjusted while racing ". However natural distortions are possible with the use of preshaped material.

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Passively, I wonder if there is energy that can be captured and redirected from wave or other gravity-induced fluctuations.

There are, of course, designs for harvesting energy from the movements of the tides, so it's not a completely crazy question.

 

But the laws of thermodynamics are against you when it comes to storing and recovering energy from a spring.

 

You can never get more energy out of the system than you put in (conservation of energy).

 

You can never get all of the energy back out of the system that you put in (entropy increases).

 

The energy that goes into the original movement will not all come back out in the subsequent movement, and it will never exceed the original input.

That doesn't mean that a springy foil cannot be more efficient than a rigid foil.

 

All it means is that any "passive flapping" done by the foil is not going to accelerate the boat.

 

It may, if you're a brilliant designer, keep the foil from dragging as much as a different design.

 

Or it may help stabilize the boat in some other fashion.

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^ Could the foils be riding on 'springs' instead of rigidly locked down? Any 'spring' energy might then be the result of input from wave, wind, or 'gravity' bounces. Energy you could recover, maybe like how regenerative braking is done.

 

Agreed it is a bit crazy, so thanks for toying with the idea anyway.

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board....

http://www.tspeer.com/Aclass/A-ClassCatamaranFoils.pdf

Well - thx.

 

I was really trying to use the foil pair of an A Class platform as a straw man for understanding a single TNZ style foil. And I guess it's not all for naught.

 

It would seem that asymmetric loading - it's a sailboat after all - means that the behavior of port and starboard boards is different (even though the boards are exactly the same shape). From the slide deck:

 

Drag increases as boat flies higher

Lift and drag shift to leeward board

 

I understand that lift decreases on the windward board because of leeway - but drag may be limiting a corresponding increase in lift on the leeward foil - if I understand correctly.

 

On the other hand - it could be using a pair of matching foils is not an ideal model of a single uptip foil. Still - the fact that an A doesn't drop its sailor in the drink (tea bag) with increased leeway - is intriguing.

 

A couple new phrases in the deck: Heave stiffness (for you spring theorists). And pitch-heave coupling (for the bow down aficionado).

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Here's a brain teaser. It was reported that a pair of A class z foils can behave like a single uptip foil - in terms of leeway coupling. I guess the notion is that a pair of lifting surfaces = 1 dihedral board....

http://www.tspeer.com/Aclass/A-ClassCatamaranFoils.pdf

...

Drag increases as boat flies higher

Lift and drag shift to leeward board

...

This analysis only considered the induced drag due to lift, not the total drag. The parasite drag will decrease as the wetted surface decreases. So the total drag should initially drop as the boat flies higher, but then increase as the wetted span is shortened to the point that the increase in induced drag outweighs the decrease in parasite drag. But the effect of leeway on lift and righting moment should be correct, within the limits of lifting line theory. Unfortunately lifting line theory doesn't capture the effects of the free surface, so there are still a lot the physics that are left out.

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Thanks. Honestly I felt I had it wrong there: induced drag - not parasitic drag.

 

Prandtl theory aside (crap - I was looking through microscopes in college!) I wonder if one of the reasons the best sailors of flying boats seem to have such unaccountably twitchy tillers - is to shrug off some of the ill effects of leeway.

 

I suspect they can feel something happening to the boards - while sailing - that simply cannot be observed - by watching.

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Back to the theory that leeway decreases the lift on an L foil with uptip,. I can see 3 main reasons:

- because of the turbulence under the lifting surface (if the tip has a correct angle vs the vertical part when the leeway occur)

- because, as the vertical surface diminishes, thus the lifting one has to sustain more load for a same speed and lift, thus decreasing the altitude

- because of the leeway the rudder foil lift the stern, thus giving less aoa to the main foil.

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^ Could the foils be riding on 'springs' instead of rigidly locked down? Any 'spring' energy might then be the result of input from wave, wind, or 'gravity' bounces. Energy you could recover, maybe like how regenerative braking is done.

You can never get more out of a spring than you put into it (law of conservation of energy).

 

You can never get all the energy out of a spring that you put into it (law of increasing entropy).

 

Pushing the spring-loaded foils into loaded position is going to rob the boat of some forward momentum. The energy to cock the spring has to come from somewhere.

 

It's true that you might get SOME of the back, but never all of it. Some of the energy robbed from elsewhere is going to turn into heat and become incapable of doing work.

 

That doesn't mean that there is no advantage in using springs as shock absorbers or some kind of dampening system, at least in theory.

 

I wonder how big the springs would have to be to take the loads involved in foiling these boats. I think there is a weight limit for the whole boat and all of its systems.

 

I don't know whether it is true of boats, but in the radio-controlled hobby, people say, "Lighter flies better."

 

Having said all that, the kind of advantage that I think people envision is a relatively flexible foil that bends to an optimum setting under load, as some airplane wings do quite noticeably in flight. That's a whole different kettle of fish.

 

Agreed it is a bit crazy, so thanks for toying with the idea anyway.

If you could get net positive propulsion out of a spring-loaded foil, you would have the makings of a perpetual-motion machine. That is definitely "a bit crazy." :D

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Van West was asked by CSN(Martin) "Will the 4 foil setup will equal or better 3 foil NACRA 20FCS set up?"

 

We believe so, by designing the boards such that there is a leeway-coupling effect between the two surface piercing daggerboards, this effect together with the fluctuating surface area of the foil effected by the flight height makes the boat 'Heave Stable'.

 

------------------

Of course, this configuration is illegal on the AC boats...........

 

 

We wouldn't want poor old Oracle getting blindsided again so no wonder.

 

 

It's not illegal though - just another DL 'misunderstanding'......

 

4509206-md-510x371.jpg

 

 

Illegal because the windward board cannot be used to create RM..... Apparently the windward board does not have to be retracted as it did in the past?

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I thought I remembered a rule to the effect that the windward board had to be retracted. I just checked the AC 50 rule and the AC72 rule and there is no such restriction. The only restriction-that I can find- is not using the windward board for RM. So theoretically two surface piercing boards could be used as long as they can be shown to not increase RM. Two lifting surface piercing daggerboards on either side of the boat would reduce total righting moment so I don't see the advantage on an AC boat.

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The A cat has the design challenge of marrying a pair of foils that must: lift horizontally, lift vertically, and operate successfully (fully immersed) on either tack = mind officially blown.

 

In other words, a single foil (design structure) must operate simultaneously in opposing regimes: one board with lateral load on the outside, and the other with lateral load on the inside. The fact that this can even be done is a testimate to the designer's ingenuity.

 

OTOH, the latest iteration of L foils, as demonstrated by Team Japan for example, seem trivial in terms of the design problem. Loads are consistent in direction - and a pair of orthogonal foils are dedicated to either horizontal or vertical load.

 

Therefore, unless somebody can do better than an L foil - the design challenge this time around would seem to be weighted towards the control system - and not so much the foils anymore.

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In other words: the design problem created by keeping four foils down seems immeasurably more complicated - and inherently less efficient - than swimming a single lifting surface dedicated to lift in a single direction.

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Floater-the UptiP foils lift in two directions: vertically(for lift) and horizontally(for lateral resistance). The interaction between those is what "leeway coupling" is all about and why the uptip foil has a range(s) of automatic heave stability-not generally speed dependent like a surface piercing foil*.

 

A-Cat "Z" foils are surface piercing.....

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Yes, the uptip foil is "two dimensional". But when I look at Team Japan's foil - I don't see a TNZ style board (ironically).

 

I see a near perfect L foil. A "one dimensional" board that would seem to rely less on leeway coupling and more on Herbie coupling.

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And to push an analogy too far: the Z foil is a "three dimensional" design challenge - because it must operate with lateral forces on either side of the dagger - which switch from port to starboard tack.

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You simple creature, I attach a labelled diagram to explain to you why configuration and orientation of similar foil shapes WILL give different outcomes to heave stability and ride height. ETNZ style foils were proportional in how they generated lift and traded that lift with reduced leeway resistance in a predictable and controllable manner. But when these foils are set vertically or canted outward - that proportional relationship is lost and either higher level foil control is required OR you resort to the Lurching Hip Hop style of flight control that you yourself, are all too familiar with.....

 

I have consistently said that the new orientation and configuration are only possible because of the higher level of foil control that is available now, and this includes active Rudder control. I have also consistently said that there are a lot of parallels between foils from last to current cup cycle - but all of this reinforces why foils with 90 turns should not be labelled uptip (try T, L or Tick) and why it is misleading.

 

All of this would also explain why, how without such refined foil control and not previously being allowed to have active rudder control, that Foil shapes as shown in Post #329 were not flight stable to the extent that ETNZ had flight stability.......)

 

Flame on biplane boy. Cant wait for the red ink and indignation. I have fresh popcorn kernels ready for the weekend.......

 

 

 

You simply don't know what you're talking about.

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Yes, the uptip foil is "two dimensional". But when I look at Team Japan's foil - I don't see a TNZ style board (ironically).

 

I see a near perfect L foil. A "one dimensional" board that would seem to rely less on leeway coupling and more on Herbie coupling.

 

This picture shows an early foiling AC 45 with a classic "L" foil in a post where Tom Speer indicated that it has some degree of leeway coupling. It certainly uses vertical lift and generates lateral resistance simultaneously:

 

20b0efd.jpg

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And to add to the above: one of the newest foil configurations is used on the Q23 and Aeronamic 14 where the lifting foils are entirely separate from the foil that provides lateral resistance. Those boats can sail upwind with the lifting foils retracted.

Illegal on an AC boat but illustrative of the concept of separating vertical lift from horizontal lift(lateral resistance)....

 

b8qp1u.jpg

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I thought I remembered a rule to the effect that the windward board had to be retracted. I just checked the AC 50 rule and the AC72 rule and there is no such restriction. The only restriction-that I can find- is not using the windward board for RM. So theoretically two surface piercing boards could be used as long as they can be shown to not increase RM. Two lifting surface piercing daggerboards on either side of the boat would reduce total righting moment so I don't see the advantage on an AC boat.

 

In other words: the design problem created by keeping four foils down seems immeasurably more complicated - and inherently less efficient - than swimming a single lifting surface dedicated to lift in a single direction.

 

You simply don't know what you're talking about.

 

 

You need to pull your head in mate...

 

You make post after post all based on misunderstanding or misinformation - and then drag in a bunch of posters to argue over irrelavancies...

 

 

asked and answered days ago - in an attempt to clean up after you, when you last claimed the "configuration is illegal"

 

the rule you 'couldn't find' has been quoted here dozens of times from AC34 on.

 

so just stop digging

 

Haven't followed this shitfight to much, but wouldn't have worked in the last one as you were only allowed 2 foils down for a short time.

 

Has this time restraint been removed for this version.

 

The question is false - because you were allowed two foils down last time - as you are this time.

 

The significant wording has not changed, i.e.

 

11.14 Daggerboards shall not be used to generate force for the purpose or effect of increasing righting moment when used on the windward side of an AC Class

Yacht.

 

(a few of the details of when this does not apply - have been changed however)

 

 

So using a foil to lift the windward hull was and remains ok* '4x4oiling'

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nav, you're right- I was wrong that the two surface piercing foil configuration was illegal-it is legal but very problematic for an AC boat. Without downforce from the windward foil you cut RM in HALF by using such a configuration. Not to mention the "proof" that would be required to assure that the windward foil wasn't used intentionally or unintentionally for downforce.

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Aren't there still rules around when the windward board must be fully retracted? Within X secs before/after a maneuver, or mark, etc? Not that I'd expect any to 4-foil much even if they're permitted to do so, just thought the rule was still there somewhere.

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^ (a few of the details of when this does not apply - have been changed however)

 

 

Aren't there still rules around when the windward board must be fully retracted? Within X secs before/after a maneuver, or mark, etc? Not that I'd expect any to 4-foil much even if they're permitted to do so, just thought the rule was still there somewhere.

 

Short answer is again no.

 

The rule states exceptions to the 'windward board must not increase RM' however these in effect mean you are more free to deploy the windward board - not less.

 

In the circumstances mentioned (see (a) - (e) below) you do not have to worry about 'proving you are not increasing RM' (as you presumably would at all other times when using 2 'daggerboards', if challenged) - in fact you are free to produce all the negative lift if you want.

 

 

11.14 Daggerboards shall not be used to generate force for the purpose or effect of increasing

righting moment when used on the windward side of an AC Class Yacht.

 

 

This Rule 11.14 does not apply:

(a) when the daggerboards are fully retracted (in accordance with Rule 11.6);
**

(b] prior to starting, as defined in RRSAC;

(c] when the windward daggerboard inadvertently penetrates the surface of the water for less than 10 continuous seconds;

(d) when the AC Class Yacht is within 10 seconds prior to and after tacking or gybing; or

(e) when the AC Class Yacht is taking a penalty.

 

 

 

**

11.6 When fully retracted, daggerboards shall extend no more than 0.400 m below MWP.

The Measurement Committee may install draft stripes or other references to verify that daggerboards are fully retracted.

 

( i.e. the default option to avoid protests - and maybe still the smart option, but maybe not!?)

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Which also means that the team can use an negative aoa in order to pull the board down 10 seconds after tacking or gybing.

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Which also means that the team can use an negative aoa in order to pull the board down 10 seconds after tacking or gybing.

True, but you'd think they would set a positive aoa before lowering it. Negative might help initially, to roll it, but quickly adjusting the aoa to positive at anything like the speeds they will accelerate to shortly after the tack or gybe would be very labor-power-intensive.

 

Negative aoa on the windward foil to add RM is also a bit frightening, doing it through twist at the top of the wing is more plausible.

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For max 20 seconds per tack or gybe yeah.

 

It was 60 seconds per - for AC34

 

 

Someone clearly felt it was 'plausable' enough to ban it!

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^ Nope. It's a safe 'fall back' as I said - and a bit of a relic from the AC72 Rule.

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^ Sure looks like it. Thanks again for posting all the relevant language.

 

How on earth would they monitor compliance, assuming anyone did build RM that way?

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For max 20 seconds per tack or gybe yeah.

 

It was 60 seconds per - for AC34

 

 

Someone clearly felt it was 'plausable' enough to ban it!

 

What version of the AC72 rule to you find that in?

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30 secs before or after a maneuver (60 secs total) does sound longer than what I remember (thought it was 10/20) but it's certainly possible and nav likely has the latest AC 34 docs, as do I somewhere findable.

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A bit of background for those not paying attention - but with lots of opinions anyway

 

 

I guess it has occurred to you all by now that 'we' are not in the loop, rule-wise. They are either not published or are subject to repeated change - usually both!.....

So bearing that in mind; the same set of limits were originally to apply to AC35, as far as 4 x foiling goes, as applied in AC34 - except the significant time restriction has been reduced - twice.... see (d) - ( was 30 seconds in the AC72 Class Rule )

 

AC62 Class Rule V 1.0

11.13 Daggerboards shall not be used to generate force for the purpose or effect of increasing
righting moment when used on the windward side of an AC62 Yacht. This Rule 11.13 does not apply:

(a) when the daggerboards are fully retracted (as per Rule 11.5);
(b] prior to starting, as defined in RRSAC;
(c] when the windward daggerboard inadvertently penetrates the surface of the water for less than 15 continuous seconds;
(d) when the AC62 Yacht is within 15 seconds prior to and after tacking or gybing; or
(e) when the AC62 Yacht is taking a penalty.

 

 

AC Class Rule V 1.0

 

11.13. Daggerboards shall not be used to generate force for the purpose or effect of increasing
righting moment when used on the windward side of an AC Class Yacht. This Rule 11.13 does not apply:

(a) when the daggerboards are fully retracted (as per Rule 11.5);

(b] prior to starting, as defined in RRSAC;
(c] when the windward daggerboard inadvertently penetrates the surface of the water for less than 10 continuous seconds;
(d) when the AC Class Yacht is within 10 seconds prior to and after tacking or gybing; or
(e) when the AC Class Yacht is taking a penalty.

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"-it is legal but very problematic for an AC boat. Without downforce from the windward foil you cut RM in HALF by using such a configuration." said fLoriDoughboY

 

Not true.

 

Consider a race run in the lowest TWS allowed.

 

You would want all 4 foils down - the boat to achieve flight first & maintain it, will kill its opposition that can't.

Achieving flight mode and all the performance gains that it brings would be a much higher priority over maintaining maximum RM.

 

When the apparent has built and the boat begins to get over powered you would retract the windward foil thereby restoring maximum RM.

 

Which circles back to having really advanced foil control systems (as well as good foils)........ sound familiar?

 

 

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Going from 15 to 10 is probablly a safety measure. However, even though difficult to enforce, a yacht letting a board fall in the water 11 seconds before the tack, or still on the ww hull 11 seconds after a tack could be penalized. We can guess teams will check that.

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Going from a minute (total) to 30 seconds to 20 seconds you mean. How do you see that as a 'safety measure'?

 

Do you think the original AC34 ban on sailing with 'increased righting moment produced by the windward daggerboard' for big parts of the race was put there on the basis of safety rather than simply banning yet another area of design that OTUSA did not want to compete in? Remember this was in place for non-foiling AC72s (unless it was added as an amentment after ETNZ showed how to fly?)

 

Or do you mean 'safety' in the ironic, wink wink IM way, of forcing in a change wanted by a 'mate' - that would otherwise not be accepted?

 

Note that under the AC72 rule it was up to the protesting team to 'prove' somehow the rule was infringed. (>RM)

 

For a protest against a Competitor under this rule to be upheld, it must be proven to the complete satisfaction of the Jury that this rule has been broken.

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"-it is legal but very problematic for an AC boat. Without downforce from the windward foil you cut RM in HALF by using such a configuration." said fLoriDoughboY

 

Not true.

 

Consider a race run in the lowest TWS allowed.

 

You would want all 4 foils down - the boat to achieve flight first & maintain it, will kill its opposition that can't.

Achieving flight mode and all the performance gains that it brings would be a much higher priority over maintaining maximum RM.

 

When the apparent has built and the boat begins to get over powered you would retract the windward foil thereby restoring maximum RM. But you said "not true" above!! Which is it-you lose half the RM or not?

Which circles back to having really advanced foil control systems (as well as good foils)........ sound familiar?

 

 

 

So you're saying that each of the two foils have to be capable of lifting the total weight of the boat? And in the lightest air you want the extra drag of two foils when one foil would do the trick? Sounds crazy as hell to me! Problematic to say the least......

 

Gonzalo Redondo has a relevant comment : http://www.catsailingnews.com/2016/04/a-cat-applied-tech-new-z-board-racer.html#more

 

- The 4pt Z board is now being adopted in the Nacra 15, surely i nthe N17, you have designed latest Exploder foils and you have also worked in Americas Cup projects,

is there a chance to see the 4pt in coming AC for Bermuda?GR: No. Rule 11.14 says the windward board cannot be used to increase righting moment. This lack of righting moment is what makes the current 3pt configuration better than the current 4pt configurations. I would emphasise "current"

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"Point" foils???

 

 

20u3k92.png

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"-it is legal but very problematic for an AC boat. Without downforce from the windward foil you cut RM in HALF by using such a configuration." said fLoriDoughboY

 

Not true.

 

Consider a race run in the lowest TWS allowed.

 

You would want all 4 foils down - the boat to achieve flight first & maintain it, will kill its opposition that can't.

Achieving flight mode and all the performance gains that it brings would be a much higher priority over maintaining maximum RM.

 

When the apparent has built and the boat begins to get over powered you would retract the windward foil thereby restoring maximum RM. But you said "not true" above!! Which is it-you lose half the RM or not?

Which circles back to having really advanced foil control systems (as well as good foils)........ sound familiar?

 

 

 

So you're saying that each of the two foils have to be capable of lifting the total weight of the boat? And in the lightest air you want the extra drag of two foils when one foil would do the trick? Sounds crazy as hell to me! Problematic to say the least......

 

Gonzalo Redondo has a relevant comment : http://www.catsailingnews.com/2016/04/a-cat-applied-tech-new-z-board-racer.html#more

 

- The 4pt Z board is now being adopted in the Nacra 15, surely i nthe N17, you have designed latest Exploder foils and you have also worked in Americas Cup projects,

is there a chance to see the 4pt in coming AC for Bermuda?GR: No. Rule 11.14 says the windward board cannot be used to increase righting moment. This lack of righting moment is what makes the current 3pt configuration better than the current 4pt configurations. I would emphasise "current"

 

 

 

"Point" foils???

 

 

20u3k92.png

 

Yet again you demonstrate that you'll quote anything a 'designer' says, whether you understand it or not :lol: (and regardless of it's relavance - although this one was actually to the point somewhat)

 

Do 3 and 4 pt not just refer to the number of foils being used at once?? Afterall - and as quoted previously in this thread, the rule 11:14 referenced in your quote talks about when foils can be deployed and how used - but states nothing whatsoever about their shape.

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Your second paragraph sounds like it's plausible.... But the points on the illustration are also plausible. Whether you're talking about "Z", "L" or UptiP foils the boats using them ALL have 4 foils. It's not clear to me, but I think you may be right-3 foils in the water vs 4.

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Doug, reached here on your linkings, Life sometimes is not htat complicated: "4pt or 3pt" is just a simple, logical and quite descriptive way to identify how many working foils are used while airborne. A-class vs FP for ie. 'Z' foils vs 'TNZ' system.

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Well, thanks k2mav.

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No one was confused until you made it confusing.

I only refer to situations where 4 foils would be preferable to trying to foil on 3 foils - which you claim would never be the case.

The capacity for one foil to generate enough lift is not questioned - but nor does it exclude why there are situations where it would be preferable. Particularly when distribution of lift does not lead to stable or level flight.

I have already said that this situation will only occur when the wind is so light that remaining foil borne would be marginal and yet imperative.

So - to help your lack of understanding - consider an AC boat in utterly still and windless conditions.
- Attach to a tow boat
- Deploy only one of its main foils - ordinarily this would be the leeward foil - but for clarity's sake - let's just suggest that the foil is deployed within the hull that all the crew are not occupying.
- Tow from stationary to the point at which the foils generate some lift.
- You will now observe an AC boat where the hull with foil deployed, flies - whilst the other hull (containing crew) remains floating - making the whole platform cant to windward (but remember there is no wind).

- The T or L foils on the rudders are primarily stabilisers and generate only 10-20% of lift.

- Instead - repeat towing experiment - requiring both main foils deployed - but each running just enough AOA to achieve level flight - it may be required that the AOA on the crewed hull would initially be greater or slightly different than the other hull to achieve level flight - but it would be a very dynamic management - the aim being to achieve flight mode with all the drag reduction that it would entail.

- As the boat accelerates it will rise into flight mode stable, both longitudinally and awarthships.

This is why you may want to sail on four foils and not three. Just because the rig is generating thrust does not necessarily mean that that the thrust is balanced by the mass of the boat and the crew. Also that RM can be too great and needs to be managed - and not just by having the crew spread around where communication and boat handling can be made harder as a result.

 

Your spearing off into 3 & 4pt foils is another example of why the foils should just be described as C T L or Z.

 

 

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Your spearing off into 3 & 4pt foils is another example of why the foils should just be described as C T L or Z.

 

 

 

Thats amazing-you simply ignore UptiP foils which are one of the most significant developments in hydrofoils ever. The only single hydrofoil with no moving parts capable of automatically controlling flight altitude within a given range of conditions! A major innovation by Team New Zealand in 34.

And the type of foil currently used by the majority of competitors in AC 35!

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5 out of six with uptip foils-now TNZ's new test boat:

photo by Chris Cameron

 

9hm0xh.jpg

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The example of towing the foiler is worthwhile. However, it is helpful to understand that to do this more accurately requires the tow line made fast at an approximate COE (some meters up a mast). And the tow boat will not be directly ahead but instead pulling from well to leeward.

 

Melvin and ETNZ published a great video on this: the dawn of "three point" foiling, on an SL33.

 

The fact that "four point" foiling must work given unequal moments and flow across two opposing foils - means that "four point" foiling is a different problem than having a single main foil. And perhaps an even more difficult problem to solve - or so it seems to me.

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Floater, the example given by boink about towing is useless. You are 100% right-I've seen the SL33 video as well as having been involved in a lot of model testing. The tow line must be attached at the center of effort of the rig and must pull from the side to simulate the pitching forces of the rig coupled with leeway.

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I think Melvin produced his own video of same footage (and he may mention leeway coupling). Curious - in video above - no mention of coupling. At least with that original experimentation.

 

It's just a V foil granted heave stability by virtue of lesser lifting area with greater ride height.

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5 out of six with uptip foils-now TNZ's new test boat:

photo by Chris Cameron

 

9hm0xh.jpg

 

More confusion from you, good man.

 

This is a foil. Maybe old, maybe new. It's attached to a new boat, the crew is getting to grips with a new control package.

In the shot above they have allowed it to fly too high, in a few seconds it's going to nosedive spectacularly because of foil ventilation or maybe just twitchy controls and an overcorrection -who knows.

It's not supposed to do this.

The foil is neither surface piercing nor the 'other designation'* you alone insist on still using - label it 'badly utilised' if you need a label at all.

 

*your definition was most amusing though - thanks for that

 

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The only point I made is irrefutable: the foil is an UptiP foil! Regardless whether it is flown too high, it is still an uptip foil-that's just a fact. You can continue to try to ignore the technology behind uptip foils-used by most of the AC boats- because you don't understand how they work but that won't make them go away.

 

And I'm just calling the technology by the name given to it by the inventors-as you should do-if for no other reason than respect for their achievement that is still being used on AC boats today!!! Any other name for these foils is just ignorant BS.

 

Quote from the article,Part 1:

When we were working on the rule, we knew you wanted to get as much lift as possible when you were going fast downwind,” Melvin says. "For instance, in the 2010 America’s Cup, sailed on giant multihulls, the maximum amount of lift we thought we could get was about 50% of the weight of the boat. At that time, we were still relying on the hull to provide pitch control, so what’s come out of this is the boats all now have elevators (the horizontal foils on the rudders).

At Team New Zealand, we developed a new type of foil that allows you to keep your height above the water more or less steady. No one had been able to do that before, at least not on a course-racing boat that was not going downwind. We developed that mostly on our SL33 test boats -- they came with the stock constant curvature “C” foils and with those kinds of foils, you can generate 50% boat weight lift before they get unstable. But we noticed that when we could get one boat up fully foiling for a few seconds it would really accelerate away from the other boat – and that got the wheels turning. How, with such a huge potential benefit, can we achieve stable flight downwind? So our design team came up with the “up-tip” type of boards. We refined those on the 33s and our 72 is designed to do that and fortunately it worked right of the box.”

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