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Xlot

Are Z foils that much slower?

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Just wondering: couldn't Z foils - inserted from above, manual rake control through slow worm gear - solve the "hamsters" issue, be much cheaper and different enough from AC35 foils to encourage new teams entering?

 

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1 hour ago, Xlot said:

Just wondering: couldn't Z foils - inserted from above, manual rake control through slow worm gear - solve the "hamsters" issue, be much cheaper and different enough from AC35 foils to encourage new teams entering?

 

Got a pic or a link?

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Z foils are those now universally adopted by A-Class cats, the olympic Nacra17F, and M&M's TF10 tri (courtesy of DL)

http://dnaperformancesailing.com/our-boats/dna-tf10-foiling-trimaran/

http://nacra17.org/reasoning-behind-foiling-regattas-summer/

 

Both boards have to be down all the time, which does decrease the righting moment but also simplifies handling

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Logic says, two main foils in the water and a stability mechanic that relays on 'bad' slippage will always be slower than one...

But then logic certainly didn't imagine those ETNZ foils shapes and profiles, so I don't think anyone can categorically state fact either way.  

Funny how thinkers, when boxed into a corner, find a solution to a problem that didn't exist until they stood in the corner.

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4 minutes ago, Rohanoz said:

Logic says, two main foils in the water and a stability mechanic that relays on 'bad' slippage will always be slower than one...

 

But still significantly faster than displacement mode, I'm sure. Shouldn't that be enough? And, as you point out, they provide a degree of intrinsic stability ... BTW, would you have a link to an explanation of how they work?

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Just now, Xlot said:

 

But still significantly faster than displacement mode, I'm sure. Shouldn't that be enough? And, as you point out, they provide a degree of intrinsic stability ... BTW, would you have a link to an explanation of how they work?

Haven't got a link handy, but 'leeward coupling foil' is the term I would google.  Or PM Doug.

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10 minutes ago, Xlot said:

 

But still significantly faster than displacement mode, I'm sure. Shouldn't that be enough? And, as you point out, they provide a degree of intrinsic stability ... BTW, would you have a link to an explanation of how they work?

 

Quick and dirty - foils generate lift towards center of boat away from the hulls. Two mirrored wing surfaces counteracting lift and the only direction is up, giving boat lift. 

Lifting from two surfaces also gives catamaran the stability they're supposed to have, unlike the three legged AC clones. 

IMO the best solution are T foils like moths on each hull with control surfaces and auto adjusting based on simple floats. 

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ETNZ showed us the VMG gains that are made with foils that have near zero reliance on leeward coupling - but in a human controlled environment or on a smaller 'manual' boat it is currently not feasible to control them.

I wouldn't take the Olympics as any model for design or evolution in this space.  Their design philosophy is based on uniformity and production for a set timeframe, and certainly not the best or fastest of kind.  The rapid development that is foiling sailing, ensures that anything released today is obsolete by the time the Olympics come around - most likely well before then.

 

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17 minutes ago, Rohanoz said:

Haven't got a link handy, but 'leeward coupling foil' is the term I would google.  Or PM Doug.

Nooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

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Doug

New thread, same shit. How many times do you need to be told. Haven't you made a fool of yourself enough on this forum with your totally wrong pronouncements.

The link that Doug has provided is work done by M&M which compares very stable and slow Z boards (they are very big to make the boat easy to sail) with V boards that have leeward coupling. It does not compare the best Z boards with the best V boards. The fact is that very little comparative testing has been done in this regard. The closest is on the A's, where decent V foils developed by Carbonix who had the imput of a numkber of top class designers were compared with the Z foils that were around at the time. We know the V foils in question worked very well, yet the Z foils were faster and since then, the Z foils have improved a huge amount. Work done by one world class foil designer suggests that Z foils are are the preferred option over V foils and that there wouold be no advantage to the A's changing their rules.

Bringing this back to the AC, the foils they are currently using are rather different from, the V foils Doug is so fond of and insists on calling UptiP (dickhead!). The AC foils have no leeward coupling and are effectively part of the L foil family. They need constant adjustment to maintain flight height which is why there is a need for the grinders. I believe that this style of foil will always be faster in a straight line than any olther style of board. Clearly the AC guys think they are faster than V foils because those have now been consigned to AC history (not one team used them).

Z foil type boards might be a decent answer for the AC so long as they are strictly controlled to prevent anything too wild. A rule not dissimilar to the A Class with insert from above plus some limits on how the board may be moved when sailing would go a long way to providing unstablke but manageable flight (which is what we have now) without the need for constant grinding. I suspect with 3/4 years development, we would see speeds not dissimilar to the current foils.

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At the very limited public photos of the ETNZ foils, I would also hasten to add that there is as much (if not more) to be learnt about the profile sections of the boards even more so than the obvious 'gullwing' shape.  

Bit like a sail profile, the profile is almost meaningless if the twist and section shapes aren't right.  

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15 minutes ago, Rohanoz said:

At the very limited public photos of the ETNZ foils, I would also hasten to add that there is as much (if not more) to be learnt about the profile sections of the boards even more so than the obvious 'gullwing' shape.  

Agreed. The profile is the key.

The batwing shape is interesting in that it allowed them to get an effectively longer surface area under water contributing lift (within the rule constraints) when coupled with canting the foil, but the lift and drag generated is much more about the foil profile which is pretty much undetectable from examining photographs or video footage.

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7 hours ago, Xlot said:

Just wondering: couldn't Z foils - inserted from above, manual rake control through slow worm gear - solve the "hamsters" issue, be much cheaper and different enough from AC35 foils to encourage new teams entering?

 

Excellent question that I aked myself many times.

I don't think the last AC rule prevented it as the requirement is not to create rm when in the water, however no team chose it.

This is what I think:

- most of the lifting surface is more under the cat than present foils = less rm

- the winward foil in the water creates lift = less rm

- the winward foil is in the water = drag.

That said, small cats with Z foils have excellent results, and I would love to hear the explanations of an architect

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22 minutes ago, Tornado-Cat said:

- the winward foil in the water creates lift = less rm

Why does everyone assume that the windward foil must stay down just because it's a Z?

Given a bit of "toe-in" and leeway, the windward board may not produce much lift, if any, so even if left down, drag is significantly reduced and RM not hugely affected.

It seems to me the NZ foils in full cant mode were very much like Z foils.

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27 minutes ago, Tornado-Cat said:

Excellent question that I aked myself many times.

I don't think the last AC rule prevented it as the requirement is not to create rm when in the water, however no team chose it.

This is what I think:

- most of the lifting surface is more under the cat than present foils = less rm

- the winward foil in the water creates lift = less rm

- the winward foil is in the water = drag.

That said, small cats with Z foils have excellent results, and I would love to hear the explanations of an architect

I am not an architect and cannot give you the answers, but I did read an interesting interchange on Facebook between Kevin Ellway (leading foil designer) and Simon Nelson (used to post here as SimonN). Check out Ellway Aero-Hydrodynamic designs on facebook. Very cool page.

Kevin stated that theory says that on an A Class, using Z foils means you lose 1/3rd of the righting moment after taking into account leeway and other factors compared with a boat that has straight foils. I think we can all agree that is significant. Then Simon posts the results of tests that show they could find no difference in RM in the real world between  foils and a boat with straight foils. He claimed on near identical boats sailed by people of the same weight, the hulls popped up and the need to trapeze happens at the same amount of wind strength. 

I made a few enquiries about how well a Z foil boat goes upwind when not foiling compared with a straight board boat. If what we are being told is correct, surely we should see a differece based on 1/3rd less righting moment but guess what, there is none observed.

The conclusion drawn on facebook by Simon is that we don't yet fully understand what is going on. He alludes to other things that supports that, but that he wouldn't go into them on a public forum.

As said, the results seen from small cats using Z foils are pretty amazing. I think this supports the idea that we don't fully understand them and they might have a lot more potential than some realise. They don't seem to be holding the A's back.

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1 hour ago, Team_GBR said:

I am not an architect and cannot give you the answers, but I did read an interesting interchange on Facebook between Kevin Ellway (leading foil designer) and Simon Nelson (used to post here as SimonN). Check out Ellway Aero-Hydrodynamic designs on facebook. Very cool page.

Kevin stated that theory says that on an A Class, using Z foils means you lose 1/3rd of the righting moment after taking into account leeway and other factors compared with a boat that has straight foils. I think we can all agree that is significant. Then Simon posts the results of tests that show they could find no difference in RM in the real world between  foils and a boat with straight foils. He claimed on near identical boats sailed by people of the same weight, the hulls popped up and the need to trapeze happens at the same amount of wind strength. 

I made a few enquiries about how well a Z foil boat goes upwind when not foiling compared with a straight board boat. If what we are being told is correct, surely we should see a differece based on 1/3rd less righting moment but guess what, there is none observed.

The conclusion drawn on facebook by Simon is that we don't yet fully understand what is going on. He alludes to other things that supports that, but that he wouldn't go into them on a public forum.

As said, the results seen from small cats using Z foils are pretty amazing. I think this supports the idea that we don't fully understand them and they might have a lot more potential than some realise. They don't seem to be holding the A's back.

Well, well, well...

I don't know Kevin Ellway, his statement seems logic, but not of us can support the figures.

Simon always pretends to know, knows the monkey who knows the other monkey, and is often full of shit. He was the one keeping repeating Artemis boat 1 (AC34) was faster upwind because it was not a foiler. He was probably repeating some dock talk without understanding but pretended to know because sailing an A cat. He is totally unreliable, and the fact he does not want to explain is another hint that he is repeating what he heard somewhere.

More serious, the Foiling Phantom has a version equipped with Z foil. It is considered easier but not as fast as the original with the uptip foils. However, it is considered as fast or faster in some strong conditions. My guess is that it has more stability downwind and thus faster in strong conditions of wind and sea, but slower upwind because with less RM.

I wish to hear some testimonies and proves in races though.

 

 

 

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1 hour ago, RobG said:

Why does everyone assume that the windward foil must stay down just because it's a Z?

Given a bit of "toe-in" and leeway, the windward board may not produce much lift, if any, so even if left down, drag is significantly reduced and RM not hugely affected.

It seems to me the NZ foils in full cant mode were very much like Z foils.

Yes, it was an hypothesis that I made months ago, that the kiwi foil worked like a Z foil. Then I agree. However, it does not seem to reflect that as the end tip is probably flat in the water. The intermediary tip however coud work as a surface piercing water. We still wait for the explanation of the architects.....

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1 minute ago, Tornado-Cat said:

Well, well, well...

I don't know Kevin Ellway, his statement seems logic, but not of us can support the figures.

Simon always pretends to know, knows the monkey who knows the other monkey, and is often full of shit. He was the one keeping repeating Artemis boat 1 (AC34) was faster upwind because they had were not foiling. He was probably repeating some dock talk without understanding but pretended he knew because he was sailing an A cat. He is totally unreliable and the fact he does not want to explain is another hint that he is repeating what he heard somewhere.

Shows what little you know. He is Stevie Brewin and Darren Bundock's main training partner. He not only knows whats going on but he is an active part of it. He stopped posting on here because they are keeping quiet about everything they are doing and because of idiots like you and Doug Lord. Now I can see why.

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10 hours ago, Miffy said:

 

IMO the best solution are T foils like moths on each hull with control surfaces and auto adjusting based on simple floats. 

 

Perhaps, but not in offshore conditions. Keep in mind GD's statement about the next Cup boat having to be seaworthy

 

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7 hours ago, A Class Sailor said:

Shows what little you know. He is Stevie Brewin and Darren Bundock's main training partner. He not only knows whats going on but he is an active part of it. He stopped posting on here because they are keeping quiet about everything they are doing and because of idiots like you and Doug Lord. Now I can see why.

Simon ?

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Quote

A Cat Sailor - Z foil type boards might be a decent answer for the AC so long as they are strictly controlled to prevent anything too wild. A rule not dissimilar to the A Class with insert from above plus some limits on how the board may be moved when sailing would go a long way to providing unstablke but manageable flight (which is what we have now) without the need for constant grinding. I suspect with 3/4 years development, we would see speeds not dissimilar to the current foils.

 

 

Quote

Tornado-Cat -  the Foiling Phantom has a version equipped with Z foil. It is considered easier but not as fast as the original with the uptip foils. However, it is considered as fast or faster in some strong conditions. My guess is that it has more stability downwind and thus faster in strong conditions of wind and sea, but slower upwind because with less RM.

 

 

Quote

Team_GBR - Kevin stated that theory says that on an A Class, using Z foils means you lose 1/3rd of the righting moment after taking into account leeway and other factors compared with a boat that has straight foils. I think we can all agree that is significant. Then Simon posts the results of tests that show they could find no difference in RM in the real world between  foils and a boat with straight foils. He claimed on near identical boats sailed by people of the same weight, the hulls popped up and the need to trapeze happens at the same amount of wind strength. 

I made a few enquiries about how well a Z foil boat goes upwind when not foiling compared with a straight board boat. If what we are being told is correct, surely we should see a differece based on 1/3rd less righting moment but guess what, there is none observed.

The conclusion drawn on facebook by Simon is that we don't yet fully understand what is going on. He alludes to other things that supports that, but that he wouldn't go into them on a public forum.

As said, the results seen from small cats using Z foils are pretty amazing. I think this supports the idea that we don't fully understand them and they might have a lot more potential than some realise. They don't seem to be holding the A's back.

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Thanks all for the valuable contributions. It seems to me that Z foils could indeed solve several issues outstanding with multihulls in the AC: on AC50s, they would eliminate the need for "hamsters" and lower the entry barrier for new teams, while retaining used market value of existing AC50 hulls. On soft-sail AC62 cats or MOD70 tris, they would tick the "seaworthy" case while the crew would be busy on traditional tasks ...

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15 hours ago, Team_GBR said:

I am not an architect and cannot give you the answers, but I did read an interesting interchange on Facebook between Kevin Ellway (leading foil designer) and Simon Nelson (used to post here as SimonN). Check out Ellway Aero-Hydrodynamic designs on facebook. Very cool page.

Kevin stated that theory says that on an A Class, using Z foils means you lose 1/3rd of the righting moment after taking into account leeway and other factors compared with a boat that has straight foils. I think we can all agree that is significant. Then Simon posts the results of tests that show they could find no difference in RM in the real world between  foils and a boat with straight foils. He claimed on near identical boats sailed by people of the same weight, the hulls popped up and the need to trapeze happens at the same amount of wind strength. 

I made a few enquiries about how well a Z foil boat goes upwind when not foiling compared with a straight board boat. If what we are being told is correct, surely we should see a differece based on 1/3rd less righting moment but guess what, there is none observed.

The conclusion drawn on facebook by Simon is that we don't yet fully understand what is going on. He alludes to other things that supports that, but that he wouldn't go into them on a public forum.

As said, the results seen from small cats using Z foils are pretty amazing. I think this supports the idea that we don't fully understand them and they might have a lot more potential than some realise. They don't seem to be holding the A's back.

I thought about this stuff until my head exploded. Then decided that hydrodynamics best left to Speer and co.

still - it seems to me that because of leeway, the angle of incidence on port and starboard foils will never be equal. So - although the paired z foils appear symmetric (on the beach - looking at them) they are in fact far from symmetrical wrt water flow and pressure while under way. 

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16 hours ago, A Class Sailor said:

Shows what little you know. He is Stevie Brewin and Darren Bundock's main training partner. He not only knows whats going on but he is an active part of it. He stopped posting on here because they are keeping quiet about everything they are doing and because of idiots like you and Doug Lord. Now I can see why.

 

9 hours ago, Tornado-Cat said:

Simon ?

Surprised that he would be sailing with those guys or surprised that he would actually knows what is going on? Just shows that you never know who is behind a keyboard. For all we know, you might be a decent guy in real life :D

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1 hour ago, A Class Sailor said:

 

Surprised that he would be sailing with those guys or surprised that he would actually knows what is going on? Just shows that you never know who is behind a keyboard. For all we know, you might be a decent guy in real life :D

I don't pretend to know, but your first sentence is a signature :)

Anyway, if that''s the case, your participation is much more positive under the new alias, which means we can perhaps get along..............behind a keyboard :o.

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1 hour ago, Tornado-Cat said:

I don't pretend to know, but your first sentence is a signature :)

Anyway, if that''s the case, your participation is much more positive under the new alias, which means we can perhaps get along..............behind a keyboard :o.

I misunderstood. You think I am SimonN.:lol: Whatever. Maybe this should be an "I'm Spartacus" moment, if that makes you happy.

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From experience in the A Class, I am with A Class Sailor in that SimonN has good information. 

Floater, you are right.  Leeway can be a signifiant factor with Z foils and that can transfer the lift primarily to the leeward foil.

Several of us sail Z foil boats and they can work well and are less energy intensive as they are passive.  Interesting idea for the America's Cup.  Wand or sensor based foils could also be intriguing and are just a step further than what ETNZ had.  

The AC50s had to have three point foiling because their rules dictated the windward board must be retracted.  This rule as I understand it came from the prior Cup to avoid windward board downforce designs.  They could not try 4 point Z systems even if they wanted to.

Side note: I personally didn't like the level of downforce the teams ran in the rudders in this Cup because if the boats healed and exposed the windward elevator, they lost pitch control and went nose in.  The prior Cup's boats with their ability to heal and still maintain flight or skimming mode sailing looked a little looser and therefore a little more exciting sometimes even though they didn't perform as well.

 

 

 

 

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3 hours ago, Lost in Translation said:

From experience in the A Class, I am with A Class Sailor in that SimonN has good information. 

The AC50s had to have three point foiling because their rules dictated the windward board must be retracted.  This rule as I understand it came from the prior Cup to avoid windward board downforce designs.  They could not try 4 point Z systems even if they wanted to.

 

 

^^

You seem lost in interpretation, first with SimonN, and then with the rule.

Can you mention where the AC35 rule mentions that the "windward board must be retracted" ? :D

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On 2017-06-29 at 8:27 PM, A Class Sailor said:

The fact is that very little comparative testing has been done in this regard. WRONG, the Flying Phantom has been compared to the Essentiel equipped with Z foils.

The closest is on the A's, where decent V foils developed by Carbonix who had the imput of a numkber of top class designers were compared with the Z foils that were around at the time. We know the V foils in question worked very well, yet the Z foils were faster and since then, the Z foils have improved a huge amount. Work done by one world class foil designer suggests that Z foils are are the preferred option over V foils and that there wouold be no advantage to the A's changing their rules. WRONG, the Phantom Essential has been considered slower in most conditions (with a few exceptions).

Z foil type boards might be a decent answer for the AC so long as they are strictly controlled to prevent anything too wild. A rule not dissimilar to the A Class with insert from above plus some limits on how the board may be moved when sailing would go a long way to providing unstablke but manageable flight (which is what we have now) without the need for constant grinding. WHY ? Z foils are generally considered more stable than the 3 points ones, and it makes sense.

I am not against Z foils, I just mentions that most of your points are baseless.

 

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10 hours ago, Lost in Translation said:

From experience in the A Class, I am with A Class Sailor in that SimonN has good information. 

Floater, you are right.  Leeway can be a signifiant factor with Z foils and that can transfer the lift primarily to the leeward foil.

Several of us sail Z foil boats and they can work well and are less energy intensive as they are passive.  Interesting idea for the America's Cup.  Wand or sensor based foils could also be intriguing and are just a step further than what ETNZ had.  

The AC50s had to have three point foiling because their rules dictated the windward board must be retracted.  This rule as I understand it came from the prior Cup to avoid windward board downforce designs.  They could not try 4 point Z systems even if they wanted to.

Side note: I personally didn't like the level of downforce the teams ran in the rudders in this Cup because if the boats healed and exposed the windward elevator, they lost pitch control and went nose in.  The prior Cup's boats with their ability to heal and still maintain flight or skimming mode sailing looked a little looser and therefore a little more exciting sometimes even though they didn't perform as well.

It's easy to forget about the rudders. And especially that the rudders AC35 <> AC34. I guess another way to phrase this topic is "what 'set it and forget it' foiling package lends itself best towards AC36". 

And that would include both main foils and rudders. 

Keeping the purity of a foiling A class in mind, the absurdity of a row of hamsters really comes to the fore. 

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Indeed. And keep in mind the new requirement of seaworthiness, which IMO rules out wands and continuously adjusted flaps

About the stabilizer downforce - 1 ton max. now per Cammas! - it should be limited. Its effect on the forward thrust the boat can handle is so dramatic however, that crews will always squeeze the utmost (nose down etc.)

 

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8 hours ago, Tornado-Cat said:

^^

You seem lost in interpretation, first with SimonN, and then with the rule.

Can you mention where the AC35 rule mentions that the "windward board must be retracted" ? :D

I can see how you would argue the windward foil can be left down as long as it is contributing lift and not righting moment if that is what you are implying with interpretation, but even a Z board would contribute righting moment from the windward side with the lifting force vector aiming to leeward of the center of gravity of the boat.  

Rule 11.14.  

Funny to compare the Phantom Essential, a relatively low cost boat, with the Flying Phantom as a definitive proof of foil types.  One boat is widely advertised at 23K Euros and one is what, 42K Euros?  One is 8.5 foot beam and one is ~10.  One has aluminum mast and one has carbon.  One is made for accessible foiling and the other for ultimate speed.  One is also more suitable to me for short course racing for average sailors.   

I am not claiming superiority of any foil design or approach either.  It would be like arguing which type of hammer is best.  Choose the tool for the job.  

 

 

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Funny thing is, both the old crop of AC34 style j foil, as well as the A Class z foil - are creative answers to cirmumvent a design rule intended to inhibit foiling!

what do we get if we implement a rule meant for foiling: more hamsters than sailors on the yacht. 

For some reason I feel prejudice against bouncy wands and moveable flaps - not sure exactly why. But it may simply be a personal (and unsophisticated) sailing ethos: 1) Don't drag shit, and 2) fragile parts to be avoided

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All most all foil designs are constrained, to some extent by Class rules. So the present successful solutions have to be considered within the box they live in. A Class limits horizontal span and bans surface sensing wands. AC boats ban 4x4 configurations , and flaps. C Class limits beam.  GC 32 are one design. So to consider what is really possible and what may be a "best" solution you have to look someplace other than racing classes. The problem with that is that there is no testing.

Ellway's Vampire is one such out of the box example as is the Seafoiler, where the designers have sought practical answers without the type forming constraints of fair racing.

From my perspective, flaps flaps flaps flaps. They are proven to quickly and reliably alter the lift of wings. The loads are small, and can be rapidly actuated. There are some difficulties in construction, but those hydraulics were not cheap either.

SHC

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44 minutes ago, Lost in Translation said:

I can see how you would argue the windward foil can be left down as long as it is contributing lift and not righting moment if that is what you are implying with interpretation, but even a Z board would contribute righting moment from the windward side with the lifting force vector aiming to leeward of the center of gravity of the boat.  

Rule 11.14.  

Funny to compare the Phantom Essential, a relatively low cost boat, with the Flying Phantom as a definitive proof of foil types.  One boat is widely advertised at 23K Euros and one is what, 42K Euros?  One is 8.5 foot beam and one is ~10.  One has aluminum mast and one has carbon.  One is made for accessible foiling and the other for ultimate speed.  One is also more suitable to me for short course racing for average sailors.   

I am not claiming superiority of any foil design or approach either.  It would be like arguing which type of hammer is best.  Choose the tool for the job.  

 

 

In fact I love the concept of the Z foils and I wish it was the best but we don't have the demonstration yet.

1 ) The AC:  rule : 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.

I don't think the Z foil can increase the RM except perhaps with leeway ? I don't think so because the lifting profile of the windward foil would probably not allow it. I am not an architect and cannot give a definite answer. But if the 4 points foil solution was a good solution, the AC architects could have worked on it and they did not.

2) A cats: difficult to know as most of them use Z foils because of their rule. How to compare a tested Z foil with a V that is does not compare ?

3) 18ft and 20 ft cats like the Flying Phantom and the Essential, the Nacra, the Vampire Projet : they may give us the solution and as far as now it goes toward the 3 points sailing.

A agree with you, the difference in the offer between the FP and the essentiel is huge !

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16 minutes ago, Steve Clark said:

All most all foil designs are constrained, to some extent by Class rules. So the present successful solutions have to be considered within the box they live in. A Class limits horizontal span and bans surface sensing wands. AC boats ban 4x4 configurations , and flaps. C Class limits beam.  GC 32 are one design. So to consider what is really possible and what may be a "best" solution you have to look someplace other than racing classes. The problem with that is that there is no testing.

Ellway's Vampire is one such out of the box example as is the Seafoiler, where the designers have sought practical answers without the type forming constraints of fair racing.

From my perspective, flaps flaps flaps flaps. They are proven to quickly and reliably alter the lift of wings. The loads are small, and can be rapidly actuated. There are some difficulties in construction, but those hydraulics were not cheap either.

SHC

Agree with you, however:

- AC: the 4 points is not prohited by the rule as mentionned below

- A cats: totally agree

- GC 32: yes

- Small cats : they are going to give us the answer between the V, Z, L, W (whomper), flaps + wand.

I think that planes give us the solution and, as you say, it will be flaps + manual or wands controls.

It will be then used on MOD70

 

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12 minutes ago, Steve Clark said:

From my perspective, flaps flaps flaps flaps. They are proven to quickly and reliably alter the lift of wings. The loads are small, and can be rapidly actuated. There are some difficulties in construction, but those hydraulics were not cheap either.

 

I can see your point, Steve - and congrats on your UFO. But perhaps not for comparatively heavy, offshore boats, no?

 

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2 hours ago, Steve Clark said:

..

From my perspective, flaps flaps flaps flaps. They are proven to quickly and reliably alter the lift of wings. The loads are small, and can be rapidly actuated. There are some difficulties in construction, but those hydraulics were not cheap either.

SHC

Thanks, flaps have been my (swag) hope too for what direction AC foilers would go next.

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Above it is mentionned that some real world testing has demonstrated that a foiler and a straitgh board similar A-cat will fly the hull excatly at the same time in similar conditions and then the conclusion is that both have same righting moment.

That is true, but only in 6knts TWS when both are sailing windward and flying a hull as floaters

In different wind conditions, the RM might be very different.

So I dont understand what this experience is supposed to demonstrate.

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17 hours ago, Tornado-Cat said:

The fact is that very little comparative testing has been done in this regard. WRONG, the Flying Phantom has been compared to the Essentiel equipped with Z foils.

The closest is on the A's, where decent V foils developed by Carbonix who had the imput of a numkber of top class designers were compared with the Z foils that were around at the time. We know the V foils in question worked very well, yet the Z foils were faster and since then, the Z foils have improved a huge amount. Work done by one world class foil designer suggests that Z foils are are the preferred option over V foils and that there wouold be no advantage to the A's changing their rules. WRONG, the Phantom Essential has been considered slower in most conditions (with a few exceptions).

Z foil type boards might be a decent answer for the AC so long as they are strictly controlled to prevent anything too wild. A rule not dissimilar to the A Class with insert from above plus some limits on how the board may be moved when sailing would go a long way to providing unstablke but manageable flight (which is what we have now) without the need for constant grinding. WHY ? Z foils are generally considered more stable than the 3 points ones, and it makes sense.

I am not against Z foils, I just mentions that most of your points are baseless.

Maybe I didn't make myself clear enough because you cannot compare the performance of the FP with the Essential and draw conclusions. There has not been a serious study done where the object was to achieve the maximum speed around a course from Z foils to compare with the best V foils. The Essential design brief was around safe, easy foiling. If they had designed for speed, they would end up with a different design of Z foil. Span and section change the characteristics and performance a lot, which is why one of the A Class builders is now up to the 19th version of their foils and why speeds have increased by close to 30% in a year.

The A Class is the only time we see Z foils being developed for maximum speed round a course. There have been attempts to develop both V foils and Moth style T foils with wands (same as the S9 Stunt) for the A and in both cases, they were slower than what was being achieved by Z foils which is one of the reasons why people have dropped the idea of changing the A Class rules on foils. It is true that both the V and T foils made the boat a bit easier to sail in a straight line, but the V foils needed the windward foil to be raised which lost a lot of time, adding to the overall loses around the course.

To understand speed potential of different configurations for the AC boats, it would need a specific study done where limitations are removed

When looking at foiling cars and configurations, you see that the only boats foiling consistently upwind are the AC boats. With almost all the other cat foilers, upwind foiling doesn't or rarely pays around a race course. The only other cat that it does pay on is the A, but only in over about 12 knots and only with the very top sailors. It will be interesting to see how the Nacra 17 goes in this respect.

Even the picture with the A's is distorted by the rules and by time put into development. We don't know if Z foils can be even faster if the limits imposed by the A Class rules were relaxed but we also know that more time has been spent developing A  Class Z foils than any other foils in the cat world other than the AC. That development has also been done by AC designers, so again the picture is distorted.  This is why I say we have not seen any proper comparisons and that we cannot draw any conclusions.

All of this is a bit of a distraction because while Z foils are clearly an alternative for the AC, this might not be the issue we should be discussing. I suspect the real solution to the "hamster" issue mentioned by the OP is around the rules of how much you can move the foils when sailing and how you do that. The type of foil doesn't change that very much because if you set a type of foil and a limit on how it moves, the teams will come up with a design solution that works. it might not be the fastest it could be without the limitations, but because of the time and money put into development, you can bet that whatever the rules say, the end solution will be more than fast enough. Allowing 4 point foiling will reduce the amount of oil that needs to be pumped because you no longer have to raise and lower boards and I suspect that this would allow cheaper foil case solutions. Maybe the fact they lift the boats well into the air means they could do away with the need to ever raise and lower the boards, simply fitting the boards in the down position before launching like they do with the rudders

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3 hours ago, A Class Sailor said:

Maybe I didn't make myself clear enough because you cannot compare the performance of the FP with the Essential and draw conclusions. There has not been a serious study done where the object was to achieve the maximum speed around a course from Z foils to compare with the best V foils. The Essential design brief was around safe, easy foiling. If they had designed for speed, they would end up with a different design of Z foil. Span and section change the characteristics and performance a lot, which is why one of the A Class builders is now up to the 19th version of their foils and why speeds have increased by close to 30% in a year.

The A Class is the only time we see Z foils being developed for maximum speed round a course. There have been attempts to develop both V foils and Moth style T foils with wands (same as the S9 Stunt) for the A and in both cases, they were slower than what was being achieved by Z foils which is one of the reasons why people have dropped the idea of changing the A Class rules on foils. It is true that both the V and T foils made the boat a bit easier to sail in a straight line, but the V foils needed the windward foil to be raised which lost a lot of time, adding to the overall loses around the course.

To understand speed potential of different configurations for the AC boats, it would need a specific study done where limitations are removed

When looking at foiling cars and configurations, you see that the only boats foiling consistently upwind are the AC boats. With almost all the other cat foilers, upwind foiling doesn't or rarely pays around a race course. The only other cat that it does pay on is the A, but only in over about 12 knots and only with the very top sailors. It will be interesting to see how the Nacra 17 goes in this respect.

Even the picture with the A's is distorted by the rules and by time put into development. We don't know if Z foils can be even faster if the limits imposed by the A Class rules were relaxed but we also know that more time has been spent developing A  Class Z foils than any other foils in the cat world other than the AC. That development has also been done by AC designers, so again the picture is distorted.  This is why I say we have not seen any proper comparisons and that we cannot draw any conclusions.

All of this is a bit of a distraction because while Z foils are clearly an alternative for the AC, this might not be the issue we should be discussing. I suspect the real solution to the "hamster" issue mentioned by the OP is around the rules of how much you can move the foils when sailing and how you do that. The type of foil doesn't change that very much because if you set a type of foil and a limit on how it moves, the teams will come up with a design solution that works. it might not be the fastest it could be without the limitations, but because of the time and money put into development, you can bet that whatever the rules say, the end solution will be more than fast enough. Allowing 4 point foiling will reduce the amount of oil that needs to be pumped because you no longer have to raise and lower boards and I suspect that this would allow cheaper foil case solutions. Maybe the fact they lift the boats well into the air means they could do away with the need to ever raise and lower the boards, simply fitting the boards in the down position before launching like they do with the rudders

Thanks for your detailed an thorough answer.

You surely know more than I do, about V foil test with the A cat, but what I saw were mainly test with Z foils because of the rule, and you know better than me that the rule was not amended as required by some. The only serious try I have seen was Petrucci, and he was seriously attacked by some old stubborn and narrow minded A cat sailors.

Also this question marks:

- If Z foils were faster, why would Phantom use it to make a slower one ?

- As Z were not prohibited from the AC why no team chose to use it ?

- If Z foil are faster why don't they win at open races like Texel and the Raid Eurocat ? in fact see either uptips or the Vampire

- The Nacra 17 have Z foils designed for speed, why don't we see it winning the Eurocat, Texel or other similar event ?

 

 

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Tornado Cat,

The only serious try I have seen was Petrucci, and he was seriously attacked by some old stubborn and narrow minded A cat sailors.

You dare everything, including mentionning Bimare which has disappear from the cat industry

How many bimare boats did you buy and sail in the past ??

Last market niche bimare had was the French market, but after a young 23 old lady died in a capsize on a bimare F16 in June 2013, bimare boat were less appealing for the french sailors despite special price arrangments.

This accident occured on the lake of Sanguinet at 50 m from the RC boat, but weather conditions were terrible around 12 knts wind and 3 inches chop.(many top A-cat sailors know the place)

That is why bimare seeks desperatly to sell their stuff on new markets where they have no bad records, and that is why they have changed their name, it is not bimare anymore.

Importers of these boats should perform a thorought due-diligence before distributing them in their own country.

If you read french or want to translate, I can post the newspapers which mentionned this sad events.

I dont wish you a good Sunday

 

 

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6 hours ago, Bench Warmer said:

weather conditions were terrible around 12 knts wind and 3 inches chop.

 

You call that terrible ? Please post the newspaper article in French.

And what has this accident to do with Petrucci foilers performance ?

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15 hours ago, Tornado-Cat said:

Thanks for your detailed an thorough answer.

You surely know more than I do, about V foil test with the A cat, but what I saw were mainly test with Z foils because of the rule, and you know better than me that the rule was not amended as required by some. The only serious try I have seen was Petrucci, and he was seriously attacked by some old stubborn and narrow minded A cat sailors.

Also this question marks:

- If Z foils were faster, why would Phantom use it to make a slower one ?

- As Z were not prohibited from the AC why no team chose to use it ?

- If Z foil are faster why don't they win at open races like Texel and the Raid Eurocat ? in fact see either uptips or the Vampire

- The Nacra 17 have Z foils designed for speed, why don't we see it winning the Eurocat, Texel or other similar event ?

 

 

A few people have tried different V foils on As, but nobody has made them go faster than the Z foils being currently used. There has also been 1 boat built with Moth style T foils. It was sailed by some top Moth sailors but never got the performance expected. The boat builder tried to get the rules changed to suit his needs with appeals to ISAF and threats of legal action, but failed. It was suggested that if he could show that the foils he was promoting were faster and no harder to use he might stand a better chance, he disappeared for the A Class scene because neither his T or V foils were even up to the speed of current A's.

-The choice of Z foils for the Essentiel had nothing to do with speed. For an easy to sail boat, they wanted a 4 foils down set up, so they didn't need to raise the windward board.

- For the AC, we are saw something completely different from the V or T style foils I was comparing the Z foils to. The L style foils were inherently unstable and needed constant adjustment making them unsuitable for most other forms of sailing. Even the best teams in the world didn't get it right all the time with touchdowns happening. Without the constant grinding, these boards would not be able to work and then we do not know what boards would be fastest. The boards used for the AC were a product of their rules, as has happened with the A Class.

- Can you show me any racing Z foil boat that has raced properly in the Texel or similar

- The N17 Z foils are not designed for speed. They are designed to make the boat relatively easy to sail. Some who have tried the boat think they have made the boat too easy at the expense of speed.The foils are very big and go a long way inboard. The good news is that because they foil relatively easily, we will see upwind foiling pay in the N17, which is pretty rare in beach cats.

I think it is important to realise that you cannot simply group all Z foils together. You can design them to have very different performance attributes (maybe that is true for all foil types). It seems to be true that just like with the AC foils, the more stable and easy they are to fly, the less speed they have. This means that when you are designing for a one design, such as the N17 or even the Essentiel, which do not have the challenge of being faster than others in the same class that we see in development classes, it is possible to favour ease of use without penalty. A 1 or 2 knot loss of speed is meaningless while in the A's, if you favour ease of use, you get left behind. For a one design, why would anybody go to the lengths that we see from at least one builder in the A's, who is now up to the 20th iteration of Z foils because I believe that when designing for a one design, as soon as the foils display the right handling characteristics, you would stop development. The thing that distorts the picture is the limits placed by the A Class rules. Nobody knows what would happen if we opened the rules up but what we believe is that we have been pushed into the faster, less heave stable end of the Z foil continuum  but that the unstable nature of the foils is still at an acceptable level for the vast majority of those who would sail an A.

This "game" is changing so fast. Look at the A's (sorry to keep using them but that is where the most foil development is being done outside of the AC). Since we first saw foiling at the front of the fleet 3 years ago, we have seen a speed increase of something like 35% around a course. 3 years ago upwind foiling didn't work. Now the good guys are achieving just under 20 knots and on the same heading or higher than a standard boat. Downwind, 3 years ago they were hitting 24 knots. Now I believe it is 28 knots and going lower.

I am not aying Z foils are the answer to everything or that they are the fastest foils you can get in a total free for all situation. What i do believe is that in an evironment where you don't want to be adjusting the boards very much, the are a very good option, which is what this thread is all about.

10 hours ago, Bench Warmer said:

Tornado Cat,

The only serious try I have seen was Petrucci, and he was seriously attacked by some old stubborn and narrow minded A cat sailors.

You dare everything, including mentioning Bimare which has disappear from the cat industry

You are ill informed. He was not talking about Bimare. He was talking about a different company run by Michelle Petrucci and in particular he is talking about the S9 Stunt, a cat with 2 Moth style T foils which is selling in reasonable numbers.

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16 minutes ago, Tornado-Cat said:

Correct, S9 with wands (from Outlaw sailing)

You do know that Outlaw Sailing are only one of the distributors. The builder is Michelle Petrucci whose father owns Bimare. The important fact is that the boat is not a Bimare product.

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Z's are a good option for the A class for a number of reasons, but the the AC I would like to see foils completely unregulated other than not to protrude outside a box limit and the number of foils allowed to be used each event. I think we would very soon find out what is the best system in an unregulated environment.

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but - think we just did - hamsters required  

goal is an apparent wind boat, maneuvers suitable for match racing, but - ideally - no hamsters. 

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Allowing active control should get rid of the need for the hamster wheel. And if not why not allow battery packs. Art had a battery powered training boat so the weren't limited by grinder endurance while training/ evaluating 

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I wanted to underline that:

mentionning bimare or the S9 as a reference for the foiling cat  universe

is just like

mentionning Doug Lord and his uptip semantic as a reference for hydrofoil CFD.

To get more info about the accident, you just need to googlize 

"Le drame de Sanguinet"

What you will notice in the different newspaper articles , the journalists avoided to mention bimare, instead, the only boat mentionned is the cat she used to sail for training in her usual club a SL16, if I remenber correctly.

That is a manipulation which implictly suggests the boat involved in the accident is a SL16

But if you dig correctly, you will find the info.

The journalists had probably to comply with some crappy lobbying, just like when the French Sailing Federation try to prohibit foiling for the French National in 2016. with the same red-necks behind both manipulations.

Have a good week

 

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2 hours ago, floater said:

 

goal is an apparent wind boat in 6-30 kts wind, maneuvers suitable for match racing, but - ideally - no hamsters. 

Right. And - again - seaworthy. Plus numerous crew kept busy handling soft sails, and can be taken apart to fit into a 40' container

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Softsails?

I wonder what the sailors have to say about that. The platform and aerodynamic advantages of the wing seem tough to give up.

It seems true that absolute performance doesn't matter, but surely relative performance does.

Could they move to any boat that might be outsailed by an AC45?

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10 hours ago, Bench Warmer said:

This journalist would be better at praising Macron like all the other ones, he doesn't know what he is talking about:  "Apparemment, le cata était trop "volage", et s'est arreté net après la casse de la barre,"

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The GC32's being run in the ESS are fun enough to watch being sailed, maybe a big version would be okay. But it's JAR at that point if too similar.

The MOD 70's, do they mostly get only partial lift or can they fly full-out?

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2 minutes ago, ~Stingray~ said:

The GC32's being run in the ESS are fun enough to watch being sailed, maybe a big version would be okay. But it's JAR at that point if too similar.

The MOD 70's, do they mostly get only partial lift or can they fly full-out?

I think Gitana and Maserati are fully foiing.

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12 minutes ago, ~Stingray~ said:

The GC32's being run in the ESS are fun enough to watch being sailed, maybe a big version would be okay. But it's JAR at that point if too similar.

The MOD 70's, do they mostly get only partial lift or can they fly full-out?

 

I see your point, but at around 62' we'd be double the size, plus platform fairing w/o bracing ... one thing that should be copied from the ESS is the simplicity of transportation and setting up venues around the world

AFAIK the only flying MOD70 is the ex-Gitana Maserati, which hasn't exactly set the Catibbean on fire, being regularly beaten by the standard Phaedo 3. The Gitana team are making the full jump to an Ultime class foiling tri, should be sailing soon

 

 

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11 hours ago, Bench Warmer said:

I wanted to underline that:

mentionning bimare or the S9 as a reference for the foiling cat  universe

is just like

mentionning Doug Lord and his uptip semantic as a reference for hydrofoil CFD.

 

How about you STFU. The S9 is not bimare and even if it was, that is totally irrelevant as is an incident in an F16 in 2013, however tragic.

The S9 is a very good foiling cat and has shown the potential for T foils for wands. It work and is relatively easy to sail. In the foiling world, certain things are very binary - they either work or they do not and the S9 most certainly works. Michelle Pertucci should be congratulated on his boat and your attacks are out of order.

Lessons from the S9 and the A that was built to the same configuration here is in Australia gives us a very good idea of what the potential is. 2 T foils with wands seem to be one of the easier set ups to sail with but also seem to be limited in speed/performance. The A in that configuration barely managed an improved VMG around the course compared with the then C foil, floating boats that were the leaders. I was told that the V foil boat using the same platform and rig was faster. Upwind foiling was rather compromised and it seems the same is true with the S9. Overall, I believe that this configuration is good for the recreational market and one designs.

 

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11 minutes ago, Xlot said:

 

I see your point, but at around 62' we'd be double the size, plus platform fairing w/o bracing ... one thing that should be copied from the ESS is the simplicity of transportation and setting up venues around the world

AFAIK the only flying MOD70 is the ex-Gitana Maserati, which hasn't exactly set the Catibbean on fire, being regularly beaten by the standard Phaedo 3. The Gitana team are making the full jump to an Ultime class foiling tri, should be sailing soon

 

 

Gitana X, is it?

Drool!!!

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37 minutes ago, ~Stingray~ said:

Gitana X, is it?

Drool!!!

 

More than X, I'd say - will be launched on July 17

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Not following references to trimarans. Seems like a foiling tri would tack like shit. 

For certain a tri makes a worthy open water boat. But around the buoys - is - absurd.

if we don't stick with the general hard sail, two hull platform - which was arrived at by no accident - I'll be a monkey's uncle.

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9 minutes ago, ~Stingray~ said:

That French foil designer who is/was with ETNZ, last name biginning with a G, was he involved in the Gitana Ultime? 

Guillaume Verdier - of course

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37 minutes ago, Xlot said:

Guillaume Verdier - of course

Thanks. Presumably with others, would he have been Ultime-involved?

With GD's talk of synergy with other events then a more MOD70-like boat seems more likely, and especially if the VOR chooses that for inport racing, but Gitana may be the better indicator of the longer-term next forefront among some insider philosophers. 

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On 7/1/2017 at 7:53 AM, Steve Clark said:

All most all foil designs are constrained, to some extent by Class rules. So the present successful solutions have to be considered within the box they live in. A Class limits horizontal span and bans surface sensing wands. AC boats ban 4x4 configurations , and flaps. C Class limits beam.  GC 32 are one design. So to consider what is really possible and what may be a "best" solution you have to look someplace other than racing classes. The problem with that is that there is no testing.

Ellway's Vampire is one such out of the box example as is the Seafoiler, where the designers have sought practical answers without the type forming constraints of fair racing.

From my perspective, flaps flaps flaps flaps. They are proven to quickly and reliably alter the lift of wings. The loads are small, and can be rapidly actuated. There are some difficulties in construction, but those hydraulics were not cheap either.

SHC

I agree with all the above.  Flaps are a much better way to control foils than raking the whole thing.  I would prefer fixed rake and flaps for control on the daggerboards.  That would significantly reduce the power demands on the crew.  The control system would also be much lighter. The stabilizer could have variable incidence through rudder rake or a hinged mounting to a non-raking rudder.  Or an elevator could be added to fixed rudder & stabilizer for pitch control.

The reason the AC cats weren't allowed to use the windward board is it's impossible to ensure the windward board isn't used to generate righting moment through down force.  If a means of adding righting moment exists, the teams will exploit it.  One of the reasons for the pronounced bow-down attitude of the AC cats at high speed is they were using the allowed stabilizer deflection differentially to generate down force on the weather hull, which left them with essentially fixed collective deflection that was little different from the AC72s.  If the windward board is used to generate righting moment, then as the wind increases the structural loads increase without bound.  The team that wins is the one that operates on the very verge of breaking without going over.  It also becomes extremely dangerous when the windward board ventilates or broaches, and the righting moment it was generating is suddenly lost.  

The Vampire solution is good for performance, but it could be a disaster in close-quarter maneuvering before the start.  It would be very difficult for the pilot in the windward hull to judge the clearance between the extended leeward board and another boat.  The reason for the beam limit on the retracted part of the AC50 boards was to prevent them from taking out the shroud on a competing boat in the event of a collision.  A retracted Vampire board could be an issue in the same situation.

When you factor in the performance and safety aspects, I think the windward-retracted L foil configuration, with either L or T rudders, is the one best suited for inshore match racing.  

Now, whether the rudders are forward or aft of the foil could be an interesting question and left to the teams to decide.

Another part of the Design Rule to revisit is the maximum depth restriction.  That's what forced the kink seen in some of the daggerboard wings.  The 4.2 m circle would have been sufficient to keep the boards from becoming too long, and the combination of cant range and depth limit when retracted would have sufficed to control the wing dihedral.  If it hadn't been for the depth limit, I think you might have seen leeward-only Z foils used.

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Wow: "Leeward only Z foils used". 

Looks like somebody guessed right (OP), and to answer your question:  No, Z foils would be faster!

A 3pt. foiling cat with z foils would be something new - and unexpected - at least for me. 

But I guess a z foil could simply mean "having a tip angle downwards". The purpose of which - I suppose an end plate, more dagger surface, or both. 

Still, the big deal would be flaps. 

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2 hours ago, Basiliscus said:

I agree with all the above.  Flaps are a much better way to control foils than raking the whole thing.  I would prefer fixed rake and flaps for control on the daggerboards.  That would significantly reduce the power demands on the crew.  The control system would also be much lighter. The stabilizer could have variable incidence through rudder rake or a hinged mounting to a non-raking rudder.  Or an elevator could be added to fixed rudder & stabilizer for pitch control.

The reason the AC cats weren't allowed to use the windward board is it's impossible to ensure the windward board isn't used to generate righting moment through down force.  If a means of adding righting moment exists, the teams will exploit it.  One of the reasons for the pronounced bow-down attitude of the AC cats at high speed is they were using the allowed stabilizer deflection differentially to generate down force on the weather hull, which left them with essentially fixed collective deflection that was little different from the AC72s.  If the windward board is used to generate righting moment, then as the wind increases the structural loads increase without bound.  The team that wins is the one that operates on the very verge of breaking without going over.  It also becomes extremely dangerous when the windward board ventilates or broaches, and the righting moment it was generating is suddenly lost.  

The Vampire solution is good for performance, but it could be a disaster in close-quarter maneuvering before the start.  It would be very difficult for the pilot in the windward hull to judge the clearance between the extended leeward board and another boat.  The reason for the beam limit on the retracted part of the AC50 boards was to prevent them from taking out the shroud on a competing boat in the event of a collision.  A retracted Vampire board could be an issue in the same situation.

When you factor in the performance and safety aspects, I think the windward-retracted L foil configuration, with either L or T rudders, is the one best suited for inshore match racing.  

Now, whether the rudders are forward or aft of the foil could be an interesting question and left to the teams to decide.

Another part of the Design Rule to revisit is the maximum depth restriction.  That's what forced the kink seen in some of the daggerboard wings.  The 4.2 m circle would have been sufficient to keep the boards from becoming too long, and the combination of cant range and depth limit when retracted would have sufficed to control the wing dihedral.  If it hadn't been for the depth limit, I think you might have seen leeward-only Z foils used.

Excellent post, thanks Basiliscus.

Back to Z foils, do you think the teams did not use because they could be suspected of generating RM ? I don't think so. Or because they were just less efficient ? which I guess.

The Vampire foils could be canted inside when up so the problem could be solved.

That said, I agree that the best solution is what planes chose: fixed wing with rudder and elevator to control it. We will very soon consider AC15 as prehistoric as plane that would have to move the complete wing to change altitude, nonsense of the rule.

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10 minutes ago, Tornado-Cat said:

The Vampire foils could be canted inside when up so the problem could be solved.

You misunderstand what Basiliscus said. His concern was nothing to do with the windward, raised board but the leeward board which is canted out a fair way outside max beam when down.

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 It would be very difficult for the pilot in the windward hull to judge the clearance between the extended leeward board and another boat

I admit I am not a fan of boats that have foils outside of max beam when there is likely to be any close racing. It's fine for offshore racing, but close quarters, round the cans, I think not.

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33 minutes ago, Tornado-Cat said:

Excellent post, thanks Basiliscus.

Back to Z foils, do you think the teams did not use because they could be suspected of generating RM ? I don't think so. Or because they were just less efficient ? which I guess.

He said:

If it hadn't been for the depth limit, I think you might have seen leeward-only Z foils used.

so it's about depth.

 

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We will very soon consider AC15 as prehistoric as plane that would have to move the complete wing to change altitude, nonsense of the rule.

Aircraft actually do move the complete wing to change altitude. They use flaps (elevators) on the tailplane, it changes the aircraft pitch to change the main wing AoA (noting that speed can also be used to alter altitude). Flaps are also used to increase lift when landing and taking–off, but not to climb or descend when cruising.

I think Clivee1's Flying Cherub adjusted main foil AoA, not a flap. It was tried on Moths but I suspect it required too much power to respond quickly enough so a flap was better. But other classes with other rules might have different results (e.g. stored power actuator with bowsprit mounted sensor).

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24 minutes ago, Tornado-Cat said:

Back to Z foils, do you think the teams did not use because they could be suspected of generating RM ? I don't think so. Or because they were just less efficient ? which I guess.

You seem to have a thing against Z foils, but I think you need to keep a more open mind. I go back to Kevin Ellway, who designed the Vampire foils and the current fastest Moth foils plus much more. He knows what he is talking about. He states

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This gives the A cat a righting moment of about 2000N.m about the foil CoP. A heeled moth (see previous post) has around 2200N.m of RM. So an A cat has less RM than a moth, but has much more sail area and mast length! 

That seems pretty straight forward. Less righting moment, more sail area, taller mast, double the number of surface piercing foils and heavier should equal slower. What doesn't add up is that where RM should matter most, upwind, the top A Class sailors are now claiming to be faster and higher than the top Moths. I have read about them doing 20 knots upwind. 

It would seem to me that even if the Z foils are losing out on RM, there is something going on in terms of efficiency that allows them to go faster than the moth in a straight line upwind. Interesting stuff.

RobG

You make a very valid point. The flaps on the main wing of an aircraft are to increase lift for slower speeds by extending. Having flaps on the main foil of a boat works very differently to a modern aircraft but it does work like early planes that didn't have extendable flaps. So the current foils are more like modern aircraft while foils with flaps are rather old school when it comes to planes.

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2 hours ago, Tornado-Cat said:

...Back to Z foils, do you think the teams did not use because they could be suspected of generating RM ? I don't think so. Or because they were just less efficient ? which I guess....

WRT AC35, you need to go to the Design Rule:

6.10  In measurement condition and appendage measurement condition, no part of the AC Class Yacht shall extend more than 2.400 m below MWP.

11.2  Daggerboards shall penetrate the lower surface of the hull entirely between 7.300 m and 8.050 m forward of the stern plane, and entirely within 0.150 m transversely either side of the hull centerplane.

11.5  The maximum dimension of any daggerboard shall be 4.200 m in any direction, measured along a straight line.

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

11.7  Daggerboards, in any and all positions, shall not exceed maximum beam below MWP. Daggerboards (including fittings and control systems) may exceed maximum beam above the diagonal line formed by a point 1.000 m above MWP at maximum beam, and a point 3.000 m above MWP at 0.500 m outboard of maximum beam. No part of a daggerboard or daggerboard system shall extend beyond 0.500 m outboard of maximum beam, regardless of height above MWP.

11.10 A daggerboard shall only:
(a) be retracted or extended; and
(b) rotate around no more than two axes (or combination of the two axes) whose limits shall be determined as follows:
(i) The maximum rotation about the cant axis shall be 15 degrees with the rake axis rotation set to appendage measurement condition; and
(ii) The maximum rotation about the rake axis shall be 12 degrees and the rake axis shall be within 15 degrees of horizontal with the daggerboard set to appendage measurement condition.

These rules pretty much dictated L boards.  The reverse curvature of the shaft brought the elbow out to maximum beam for maximum righting moment, but was limited by 11.7.  The dihedral angle was limited in the negative direction by 11.6, and to some extent 11.6 also put a maximum on the radius of the elbow, depending on how much of the elbow could be tolerated in the lower bearing.  

I've not analyzed such a shape, but I'm pretty sure the minimum drag would have been obtained by a daggerboard wing that was at 90 deg to the total force vector for its entire length.  But this wasn't possible because of the depth limit of 6.10.  Instead, the wing either had to be curved so the tip was at maximum depth, or it had to have a kink that allowed the wing to run along the maximum depth line.  The higher the elbow, the more negative the dihedral could be, but that made the hull fly lower.

A Z foil could not have the amount of negative dihedral seen on the A-Class.  The A-Class has a span limit for the Z foil, but no depth limit.  The winglet of the Z foil would have been useful to produce side force at high speed, but the span of the winglet would have come out of the shaft above the elbow, raising the entire wing up above the maximum depth line.  A Z foil would also have violated the 400 mm maximum depth when retracted, even with the board canted in by the maximum 15 deg.  The winglet of the Z foil would have only been possible if the wing had enough dihedral to keep the tip of the winglet above the 400 mm line.

Draw the box yourself and see if you can fit a Z foil in it.  

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2 hours ago, RobG said:

...I think Clivee1's Flying Cherub adjusted main foil AoA, not a flap. It was tried on Moths but I suspect it required too much power to respond quickly enough so a flap was better. But other classes with other rules might have different results (e.g. stored power actuator with bowsprit mounted sensor).

Using a flap has an advantage over changing the incidence in that it moves the sweet spot of the foil.  When you increase the incidence, the angle of attack or lift coefficient for minimum profile drag does not change, and it's likely the foil will be operating away from minimum profile drag (or best profile lift/drag ratio).  But when you increase the lift using a flap, the minimum profile drag lift coefficient increases, as does lift coefficient for best profile lift/drag ratio.  This makes it more likely the foil will be operating in the zone where the profile drag is minimized.  

Of course the best performance would come from a combination of flap and incidence control so the foil always operated along the envelope of least drag for the required lift coefficient.

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Thanks, Basiliscus

"If it hadn't been for the depth limit, I think you might have seen leeward-only Z foils used"

But wouldn't very deep/slender foils conflict with the "seaworthy" requirement? Instead, I'm now very much in favor of flaps - except that, as a sop to mono nostalgics, they would be called trim tabs. That should keep them happy :D

 

 

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9 hours ago, Basiliscus said:

 Of course the best performance would come from a combination of flap and incidence control so the foil always operated along the envelope of least drag for the required lift coefficient.

Uh oh. 

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