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What will AC75 v 2 look like


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On 12/29/2021 at 6:12 AM, enigmatically2 said:

So having said I'd finished there are a couple of areas I want to look at again. First quantities:

 

Hull Surfaces - Last time 2; this time 1 legacy and 1 new, plus 1 LEQ12. Definitely favours those who went last time IMO. 

Foil arms (stocks)- last time 4 supplied. This time 4 legacy; 4 new and 4 for an LEQ 12

Foil Wings - last time 6; this time legacy 2 and new 3, but those 3 must be initially identical (rule 4.9) - and the modifiable area must be the same. Plus 4 for the LEQ12s. This seems very significant to me. It makes an LEQ 12 pretty essential if you want to try anything at all radical. Otherwise you are going to have to go with the modelling. Does it also mean that everyone will want to launch their Ac75 last to ensure they can learn from competitors? 

Foil flaps - last time 20, this time 2 legacy and 5 new - but again those must have the same initial design

Rudders - last time 4 (upper and lower separately0. this time 2 legacy; 2 new and 1 for the LEQ12

mast tubes - last time 3, this time 1 legacy; 2 new and 1 for the LEQ12

Mainsails - last time 10; this time 8 legacy skins and 12 new skins plus 8 for the LEQ 12. So contrary to what I originally thought this seems to increasingly favour the defender who will find it easier to keep new sails for the final. Also favours anyone with a boat last time where the old sails can at least be modified to work on the new one so that they can save the new ones

Headsails - last time 29; this time 10 legacy and 15 new. Ditto

So we will see far less development as the class matures this time around. What they launch with will be much closer in every respect to the final design. To me it emphasises modelling; the benefit of the LEQ 12 and of any re-use they can make of the legacy stuff.

 

 

This is all so one sided for the developers of the class of boat.   So many testing restrictions on all of the components.  This doesn’t encourage innovation, just restrictions to prevent others from learning what NZ thinks they know.

If you are new to this class and have not already bought the technology (via hiring experience designers) it is a totally waste of time/money.  This is why all of the teams are pairing up with F1 teams so they can have some greater confidence in the design software.

If NZ thinks they are better designers and sailors, why not open up the rules and prove it?

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39 minutes ago, The_Alchemist said:

This is all so one sided for the developers of the class of boat.   So many testing restrictions on all of the components.  This doesn’t encourage innovation, just restrictions to prevent others from learning what NZ thinks they know.

Yes and no. I understand what you mean and in some cases I agree. However I believe the foils that win AC37 will be very different from those that won AC36. The rule is just too different to be otherwise. Therefore all the teams have effectively one go at it. They can test scaled examples on LEQ12s or even perhaps an AC40, but there is only one real go at it on the full scale example. 

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2 hours ago, enigmatically2 said:

Anyone got a (link to a) good photo of ETNZ rules. I want to use it as basis for analysing new rule if I can

What do you mean by "a good photo of ETNZ rules"? Are you talking about the AC 75 Class Rule as used in AC 36, or something else?

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5 hours ago, accnick said:

What do you mean by "a good photo of ETNZ rules"? Are you talking about the AC 75 Class Rule as used in AC 36, or something else?

Sorry, typing on phone went awry with autocorrect. A good photo of ETNZ foils (under AC36 rules). Preferably from orthogonal to plane of foil

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3 hours ago, enigmatically2 said:

Sorry, typing on phone went awry with autocorrect. A good photo of ETNZ foils (under AC36 rules). Preferably from orthogonal to plane of foil

Thanks for clarifying, almost asked.. 

Hopefully one of us will dig up some good photos - yes it absolutely is key to AC37 too.

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Comparison of the old and new foil rules below (red is old rule, green dotted is new).

Now the most obvious difference is the 12.5% increase in width. But I am also intrigued by the fact that the max width now extends up much further than it did. The most obvious assumption is that we will get tips added to the foils. If I recall my aerodynamics, the tips on aircraft wings essentially increased lift by as much as if the lengths of those tips were added to the wing length. Assuming the same holds true for hydro-dynamics (and I have no direct evidence to support such a claim- anyone else?) this would mean that that the effective foil length would be increased by approx 30% rather than 12.5%

Now we know that they want to increase lift to improve the light airs performance, but I can't really see them accepting a penalty of increased drag in medium to high winds. And with all 3 of their AC75 foils having to be have the same initial design that means they can't pick and choose foils for conditions. Therefore they will presumably reduce drag back to Ac36 levels or below. Which all other things being equal means a reduction in the foil cord or foil thickness of approx 30%, or more likely some combination of the two.

Both of which reduce strength. And they are unlikely to be able to reduce thickness by 30% because they still need the flap controls in there. So these foils will be thinner, narrower and longer.  The higher aspect ratio will make them more efficient, but also less stable.

Hence my view that we will get more crashes, and possibly even breakages

 

foil.png

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2 hours ago, enigmatically2 said:

Comparison of the old and new foil rules below (red is old rule, green dotted is new).

Now the most obvious difference is the 12.5% increase in width. But I am also intrigued by the fact that the max width now extends up much further than it did. The most obvious assumption is that we will get tips added to the foils. If I recall my aerodynamics, the tips on aircraft wings essentially increased lift by as much as if the lengths of those tips were added to the wing length. Assuming the same holds true for hydro-dynamics (and I have no direct evidence to support such a claim- anyone else?) this would mean that that the effective foil length would be increased by approx 30% rather than 12.5%

Now we know that they want to increase lift to improve the light airs performance, but I can't really see them accepting a penalty of increased drag in medium to high winds. And with all 3 of their AC75 foils having to be have the same initial design that means they can't pick and choose foils for conditions. Therefore they will presumably reduce drag back to Ac36 levels or below. Which all other things being equal means a reduction in the foil cord or foil thickness of approx 30%, or more likely some combination of the two.

Both of which reduce strength. And they are unlikely to be able to reduce thickness by 30% because they still need the flap controls in there. So these foils will be thinner, narrower and longer.  The higher aspect ratio will make them more efficient, but also less stable.

Hence my view that we will get more crashes, and possibly even breakages

 

foil.png

One serious constraint is the ability to change certificates. The foils are listed components on the cert, and those must be declared 120 hours (five days) before the start of an event stage. Once that configuration declaration is made, you are stuck with that configuration until the end of that event stage. 

This makes it very difficult--one might say impossible--to fully optimize the foil configuration for a specific set of races. Your foils will need to have a fairly wide operating range, or you will need to be very lucky in getting a consistent set of conditions for racing at any stage. This puts a premium both on foil design, and long-range weather forecasting.

These are the key governing rules on this, but there are other clarifications withing the rule or tech regs that elaborate further.

From the tech regs:

11.11      AC75 event stage
One of:
(a)      an entire Preliminary Regatta, if raced in AC75 Class Yachts;
(b)      a Round Robin stage of the Challenger Selection Series;
(c)      a Semi-Finals stage of the Challenger Selection Series;
(d)      the Finals stage of the Challenger Selection Series; or
(e)      the entire Match,
where those regattas or parts of regattas listed above are detailed in the Protocol.
 

From the Class Rule:


32     Yacht configuration
32.1        The “declaration deadline” for an AC75 event stage shall be 120 hours before the 
scheduled start of the first race of that AC75 event stage.

32.2        Prior to the declaration deadline, Competitors shall declare confidentially to the 
Measurement Committee:
(a)      the yacht configuration to be sailed in; and
(b)      a component substitution schedule for the AC75 event stage.
 

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Another aspect of the foils that has changed is the flaps. Whilst the overall restrictions seem much the same, they now have the ability to divide the flaps up into individual segments which are separately controllable, and can apparently have different axes. I'm not quite sure what to expect here

1) Use of all segments only at low speeds and just outer segment usage at higher speeds for lower drag?

2) Bent wings with separate flap segments? (maybe like Ineos w-wings but with greater freedom so that it is now workable?)

3) Rakes wings with different wing segment rake?

4) Rake on flaps on the winglets?

 

Any views?

 

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3 hours ago, enigmatically2 said:

the tips on aircraft wings essentially increased lift by as much as if the lengths of those tips were added to the wing length

I think that a span extension is generally more efficient than an equally-sized winglet; however if the teams are all building foils to max span, I suppose we may see them   https://aviation.stackexchange.com/questions/8556/is-a-winglet-better-than-an-equal-span-extension

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6 minutes ago, porcorosso1337 said:

I think that a span extension is generally more efficient than an equally-sized winglet; however if the teams are all building foils to max span, I suppose we may see them   https://aviation.stackexchange.com/questions/8556/is-a-winglet-better-than-an-equal-span-extension

Plus the winglet would strengthen the wing spar which could allow both to be thinner which brings the winglet closer in performance. I don't think the analysis you quoted allows for that.

But as you say in any case the wing extension is not possible within the rules beyond the box. It is also worth noting that in this case that because the max foil span increases righting moment, so a winglet, by increasing lift near the end of the foil, would also improve righting moment. So I think they will be used

 

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2 hours ago, accnick said:

One serious constraint is the ability to change certificates. The foils are listed components on the cert, and those must be declared 120 hours (five days) before the start of an event stage. Once that configuration declaration is made, you are stuck with that configuration until the end of that event stage. 

This makes it very difficult--one might say impossible--to fully optimize the foil configuration for a specific set of races. Your foils will need to have a fairly wide operating range, or you will need to be very lucky in getting a consistent set of conditions for racing at any stage. This puts a premium both on foil design, and long-range weather forecasting.

These are the key governing rules on this, but there are other clarifications withing the rule or tech regs that elaborate further.

From the tech regs:

11.11      AC75 event stage
One of:
(a)      an entire Preliminary Regatta, if raced in AC75 Class Yachts;
(b)      a Round Robin stage of the Challenger Selection Series;
(c)      a Semi-Finals stage of the Challenger Selection Series;
(d)      the Finals stage of the Challenger Selection Series; or
(e)      the entire Match,
where those regattas or parts of regattas listed above are detailed in the Protocol.
 

From the Class Rule:


32     Yacht configuration
32.1        The “declaration deadline” for an AC75 event stage shall be 120 hours before the 
scheduled start of the first race of that AC75 event stage.

32.2        Prior to the declaration deadline, Competitors shall declare confidentially to the 
Measurement Committee:
(a)      the yacht configuration to be sailed in; and
(b)      a component substitution schedule for the AC75 event stage.
 

Isn't this how it was in 36? That's partially why we had those displacement battles in the low wind. Seems that TNZ are especially good at all around foils.

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4 minutes ago, pusslicker said:

Isn't this how it was in 36? That's partially why we had those displacement battles in the low wind. Seems that TNZ are especially good at all around foils.

But with fewer available you can't have different ones built for different conditions and select between them. Especially foils

 

 

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2 minutes ago, enigmatically2 said:

But with fewer available you can't have different ones built for different conditions and select between them. Especially foils

 

 

They still were locked into one set of foils for the whole round robin though? Or am I remembering it wrong?

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3 minutes ago, pusslicker said:

They still were locked into one set of foils for the whole round robin though? Or am I remembering it wrong?

Each round at a time I think. But now you are effectively locked for all qualification and final

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5 hours ago, porcorosso1337 said:

I think that a span extension is generally more efficient than an equally-sized winglet; however if the teams are all building foils to max span, I suppose we may see them   https://aviation.stackexchange.com/questions/8556/is-a-winglet-better-than-an-equal-span-extension

The winglets reduce drag.

https://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-15-DFRC.html

 

 

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2 hours ago, Stingray~ said:

e2, Did you post somewhere above a regulation that implies cyclors will be limited to a max of 4 people? 

I don't think I did, but section 19 restricts primary force input devices to either 

4 devices allowing a single person. OR 

2 devices that each allow 2 people to use

 

 

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1 hour ago, The_Alchemist said:

I think practically speaking airliners like the A320 series and B737s have winglets added to reduce induced drag without increasing span. That is vital as a larger span airplane won’t fit in the existing parking gates that the airlines have to use. 
Boeing’s latest f#@$up er I mean creation, the 787 does not have winglets only slightly curved up tips. This works as the gates these airplanes generally use accomodate much larger wingspans. 
So there is a choice to be made but the science says with no restrictions longer span is slightly better than short span plus winglets. 

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6 minutes ago, amc said:

I think practically speaking airliners like the A320 series and B737s have winglets added to reduce induced drag without increasing span. That is vital as a larger span airplane won’t fit in the existing parking gates that the airlines have to use. 
Boeing’s latest f#@$up er I mean creation, the 787 does not have winglets only slightly curved up tips. This works as the gates these airplanes generally use accomodate much larger wingspans. 
So there is a choice to be made but the science says with no restrictions longer span is slightly better than short span plus winglets. 

The latest 777X's do have massive winglets on their massive wings for parking gate reasons but I suspect those winglets are also valuable for how (like with the latest 737's) they 'fence' the wingtip flow and vortices, effectively making the wings 'longer.'

Do the new foil rules allow for vertical winglets? Do they allow for ones adjustable in length, angle, sweep?

 

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12 minutes ago, amc said:


So there is a choice to be made but the science says with no restrictions longer span is slightly better than short span plus winglets. 

I dont believe that   , can you point me towards that science.

i understand winglets to be about reducing tip vortex in a manner that recovers some energy

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3 minutes ago, breezie said:

I dont believe that   , can you point me towards that science.

i understand winglets to be about reducing tip vortex in a manner that recovers some energy

The previous poster already did. 

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10 minutes ago, Stingray~ said:

The latest 777X's do have massive winglets on their massive wings for parking gate reasons but I suspect those winglets are also valuable for how (like with the latest 737's) they 'fence' the wingtip flow and vortices, effectively making the wings 'longer.'

Do the new foil rules allow for vertical winglets? Do they allow for ones adjustable in length, angle, sweep?

 

Stinger…. Really from you, the 777x whatever while currently being vapourware, well not quite but it ain’t certified yet has no winglets only folding tips so it can move around without closing the whole airport and fit in the existing size gates. 
pic below courtesy flight global. 

5BE177C6-75D4-49D3-8D1C-DFBC437E48AC.jpeg

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Extra wing span may be better. But that is not an option here. And winglets are certainly better than increase cord length or wing thickness.

Plus in this case they move the centre of lift further out. An advantage which is not relevant on an aircraft but is massive here. 

Folding winglets are not explicitly prohibited but are worthless because of the rule that the axis must be at least 45 degrees from line of symmetry of foil wing

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58 minutes ago, amc said:

Stinger…. Really from you, the 777x whatever while currently being vapourware, well not quite but it ain’t certified yet has no winglets only folding tips so it can move around without closing the whole airport and fit in the existing size gates. 
pic below courtesy flight global. 

5BE177C6-75D4-49D3-8D1C-DFBC437E48AC.jpeg

Thanks, I stand corrected.

Those things are monsters, they take off on their test flights and fly sometimes visible from my place, the wings always look gargantuan but I (wrongly) assumed they had tips set horizontal only for testflight-safe takeoffs and then landings after sailing over the Puget Sound near Everett.

Should have known, having been inside the massive 777X wing-build facility once, although early in that facility's build. It is next to the (at one time anyway) largest-by-volume building in the world, where Boeing assembles most of their wide-bodies. Ten minutes from my place, the area is full of die-hard and proud Boeing families.

 

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22 hours ago, enigmatically2 said:

Comparison of the old and new foil rules below (red is old rule, green dotted is new).

Now the most obvious difference is the 12.5% increase in width. But I am also intrigued by the fact that the max width now extends up much further than it did. The most obvious assumption is that we will get tips added to the foils. If I recall my aerodynamics, the tips on aircraft wings essentially increased lift by as much as if the lengths of those tips were added to the wing length. Assuming the same holds true for hydro-dynamics (and I have no direct evidence to support such a claim- anyone else?) this would mean that that the effective foil length would be increased by approx 30% rather than 12.5%

Now we know that they want to increase lift to improve the light airs performance, but I can't really see them accepting a penalty of increased drag in medium to high winds. And with all 3 of their AC75 foils having to be have the same initial design that means they can't pick and choose foils for conditions. Therefore they will presumably reduce drag back to Ac36 levels or below. Which all other things being equal means a reduction in the foil cord or foil thickness of approx 30%, or more likely some combination of the two.

Both of which reduce strength. And they are unlikely to be able to reduce thickness by 30% because they still need the flap controls in there. So these foils will be thinner, narrower and longer.  The higher aspect ratio will make them more efficient, but also less stable.

Hence my view that we will get more crashes, and possibly even breakages

 

foil.png

I appreciate the time you are putting into your analysis. There was an interview with Dan B. Where he said the box was wider, and I thought he said deeper for more RM..maybe arm length?

But to extrapolate crash, break is the same as the the.."will tip over at the dock, will get luffed and fall over, will be incredibly awkward in the transition to foiling" peanut gallery that opined without data when the 36 rule was published and really had to stfu for a couple of minutes when the boats smoothly took off without a wobble.

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3 minutes ago, barfy said:

But to extrapolate crash, break is the same as the the.."will tip over at the dock, will get luffed and fall over, will be incredibly awkward in the transition to foiling" peanut gallery that opined without data when the 36 rule was published and really had to stfu for a couple of minutes when the boats smoothly took off without a wobble.

Don't get me wrong, I'm not being a doom merchant. I believe they will get it right with time. I'm just pointing out that these foils will be more extreme so they could have difficulty and be entertaining in the early stages, and the need for higher quality engineering

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1 hour ago, barfy said:

I appreciate the time you are putting into your analysis. There was an interview with Dan B. Where he said the box was wider, and I thought he said deeper for more RM..maybe arm length?

 

Unfortunately the foil arm spec is in a separate document because it is a supplied part, so I'm not sure whether its length has changed. However as I have shown above, the foil "box" is wider and deeper, both of which can be used to increase RM as I have explained

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So thinking about this some more...

All up weight of the boat has gone down by approx 11.4%

So to get the same RM they need to move the centre of lift further out. I cannot see anything about the foil arms which would be the easiest way to accomplish that, but...

The increase in foil span; increased foil box depth allowing winglets and the ability to use multiple foil flap segments will all allow that to happen. Assuming they had 2 completely independent foil flaps on either side of the line of symmetry then I reckon from some BOFP* calculations that in total those things could move the centre of lift approx 9% further from the boat centreline. But more flap segments or better control could improve that.

But at the same time that foil is producing 20+% more lift (even taking the most pessimistic assumption that a winglet produces half as much lift as a wing extension). So they are likely to want to reduce the foil to bring it back to a similar lift-mass ratio. Which means they need 30% less lift. So presumably they will reduce foil chord and foil thickness by somewhere around 30%.

So overall we could be looking at something of the order of 

11.4% less mass

Same RM

30% less hydro drag

Less aero-drag (fewer crew and no bowsprit plus more mainsail control)

So less wind would be needed for take-off even if boat speed at take-off was similar.

But if the drag really is that much less then they will presumably hit cavitation speeds more. And if they have reduced the foil chord and pushed the centre of lift out as I said, then cavitation could be worse (because the lift will come from a smaller area and thus the pressure difference will be higher). So what they do to mitigate the cavitation could be important

 

 

* for non-engineers, BOFP = Back of Fag Packet, the highly technical and accurate way we make wild-arsed guesses

 

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10 hours ago, amc said:

yeah stackexchange where the simple is made opaque.   looking further into this matter i read that winglets have the advantage at high angles of incidence whereas increased span has a slight edge at cruise.  This would suggest that winglets on the foils would be useful for breaking free

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1 hour ago, breezie said:

yeah stackexchange where the simple is made opaque.   looking further into this matter i read that winglets have the advantage at high angles of incidence whereas increased span has a slight edge at cruise.  This would suggest that winglets on the foils would be useful for breaking free

And slightly worse for the rest of the time. As I said before it is a choice the designers will have to make. 

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53 minutes ago, amc said:

And slightly worse for the rest of the time. As I said before it is a choice the designers will have to make. 

But you are comparing it to a wing extension, which is not possible here because if the rule. But winglets are better than a longer chord, especially as they increase lift at the outer end, and thus RM. 

I can't see any good reason for increasing the depth of the foil box apart from this. Can you?

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1 hour ago, enigmatically2 said:

But you are comparing it to a wing extension, which is not possible here because if the rule. But winglets are better than a longer chord, especially as they increase lift at the outer end, and thus RM. 

I can't see any good reason for increasing the depth of the foil box apart from this. Can you?

Okay several topics mashed into one here. The foil box is larger than the previous one as you showed in your diagram above. That of course allows winglets assuming that the extra span is not enough (and that is a totally reasonable assumption). 

The argument of the reason for extended tips v winglets on airplanes was what I responded to with the link not the foil. I know I know off topic slightly but that never happens here right. 

Increased lift at the outer end of the foil would only increase RM if that increased lift occurs on the outboard side of the foil only surely. Of course allowing the flaps to move independently would do this. Confounding this though is the tendency to run that tip above the water surface like we saw last time around. 

Choices! It will again be super interesting to see where the designs end up. 

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@amcmy thinking was that the inboard side would have the lift negated by putting the flaps in a neutral position. That way the winglets have no effect. But on the outboard side (or even just the outer segment) the flaps are such as to generate lift, the winglets increase that near the end, thus the centre of lift moves even further out and so RM is increased. That's a simplistic explanation because of course there is a gradual change from lift out to that situation but hopefully you get the point

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One aspect that could in theory help with cavitation would be the "foil flexures" because by smoothing the foil/flap join they can prevent localised low pressure 'hot spots'. The previous rule allowed "a flexure or soft hinge, such as a thin flexible material joining the foil flap to the foil wing"

Now there is a whole new definition of a "foil flexure" as an element of the boat: 

A region of a foil wing and/or foil flap that is declared by the Competitor as flexible

There are then a number of restrictions on them. I cannot immediately see what would be allowed under the new rule that would not have been under the original. But they have sure added an awful lot of text if there is no change

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3 hours ago, enigmatically2 said:

One aspect that could in theory help with cavitation would be the "foil flexures" because by smoothing the foil/flap join they can prevent localised low pressure 'hot spots'. The previous rule allowed "a flexure or soft hinge, such as a thin flexible material joining the foil flap to the foil wing"

Now there is a whole new definition of a "foil flexure" as an element of the boat: 

A region of a foil wing and/or foil flap that is declared by the Competitor as flexible

There are then a number of restrictions on them. I cannot immediately see what would be allowed under the new rule that would not have been under the original. But they have sure added an awful lot of text if there is no change

It appears to have been written to provide clarity about and set constraints on something that had only implicitly been allowed by the previous rule.

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21 minutes ago, accnick said:

It appears to have been written to provide clarity about and set constraints on something that had only implicitly been allowed by the previous rule.

You may well be right. I just have a hunch that there is something in there different. It could just be that they have to clarify how such a flexure works across the flap segments. On the other hand I think they will need to be looking at how to mitigate cavitation and I can't see many other options.

Special surfaces are out

Deliberately deformable surfaces are out (apart from this flexure)

I thought aeration through the foil was out, though the rule is not quite as explicit as I thought. May be something there

 

 

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16 minutes ago, enigmatically2 said:

You may well be right. I just have a hunch that there is something in there different. It could just be that they have to clarify how such a flexure works across the flap segments. On the other hand I think they will need to be looking at how to mitigate cavitation and I can't see many other options.

Special surfaces are out

Deliberately deformable surfaces are out (apart from this flexure)

I thought aeration through the foil was out, though the rule is not quite as explicit as I thought. May be something there

 

 

Seems pretty clear to me:

"5.7          Devices and finishes whose primary purpose is to reduce friction drag by altering the 
structure of the boundary layer are prohibited. This prohibition includes, but is not limited to:
(a)      electric, magnetic, sonic, thermal and chemical devices;
(b)      patterned or textured finishes, LEBUs; and
(c)      devices that suck fluid from or blow fluid on to the surface of a component.
This rule does not prohibit surface finishing permitted by Rule 5.4, passive surface features, such 
as fences or vortex generators, which extend outside the local boundary layer. The thickness of the 
boundary layer δ shall be determined using the formula:"

While this wording addresses the "primary purpose" of the prohibited features or characteristics, it does not necessarily mean that such features would be allowed for other secondary purposes. You can argue there is some ambiguity here, but I suspect any interpretation would be prohibitive.

I could be wrong.

Historically, rather than "whose primary purpose is", rules sometimes say "whose purpose or effect is".



 

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15 minutes ago, accnick said:

Seems pretty clear to me:


(c)      devices that suck fluid from or blow fluid on to the surface of a component.

Not sure. If you have a device that actively sucks then that is clearly prohibited. But if (say) there were aeration holes between the top and bottom of the foils that were only opened when the flap segments/flexures were in a certain position (the position they would be in when the boat is approaching cavitation speeds) then there is no device  sucking as such. That could then mitigate against cavitation, without reducing lift at lower speeds.

I thought that such a design was banned but I can not now find any rule that would cover it

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I'm not sold on winglets as the answer based on new iteration of the rule.  Choose your foilborne craft and I don't think you see many winglets having great success.  This is just drawing from what folks are experiencing in board (kite/wing/surf/etc) foiling and watching those foils develop.  For sake of clarity just look at Armstrong foils, which BTW are as close to AC as it seems you're gonna get in foiling at the moment. (https://www.armstrongfoils.com/)

1st gen "CF" foils were generally thicker, more anhedral and generally rounder for lack of a better term.

2nd gen HS foils trended higher aspect, thinner, flatter, and many had winglet like features (some up, some down).

3rd gen HA foils are even more high aspect, thinner and have trended to more flared ends vice winglets.

 

Some foils hit a sweet spot for certain purposes and have been kept around, but shifted between lines as things have evolved.   For example I much prefer as "early HS" 1050 for kiting to a flatter thinner more high aspect 1250 at the moment just for how I ride.

 

These foils, especially the tails, have been designed to be "chopped" in some ways to customize the feel.  Many people are "chopping" front wings as well, and the vast majority I have heard about on these foils is taking winglets off to allow surfers to recover better when the foil tips "breach."  Why does that matter here?  Remember how the best of these boats were sailed - with the tip effectively out of the water most of the time.  That means winglets don't matter for efficiency and keeping/recovering flow with the tip "breached" becomes more important.  The other aspect of this is that as people progress foiling, thinner and more HA (which are much harder to ride) are becoming more ubiquitous vice being kept at "elite" levels.  I have no doubt AC teams will figure out how to sail the most extreme foils that can be designed and built within the box.

 

Look at the attached pic of an Armstrong HA 1125 nose on and tell me it doesn't work better in the new foil box.  I'd also point out that we're all continuing to learn about hydrofoils in this world very rapidly and the rule is drawn based on what we knew almost a year ago (aka when Armstrong was testing the HA foils and they weren't quite yet in the wild.)

 

I may be wrong but the view from my seat doesn't get me to winglets.

1125.jpg

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Armstrong are doing a great job but in terms of what’s getting around a race course with a kite they are very long way off the pace, to the point that they don’t have a race foil 

they are deep into the winging and foil surfing 

 

for race foils it’s chubanga, levitatz and Mikes Lab that a way out in front, 

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Does any body know what the weight of the foils of the Te Kahu AC40 will be?
This is what the Draft version Tech Regs 1A says about it:
253656040_AC40dimensionsandweight1.png.c768707fcc8038218a2d6e85860d0a20.png
454878290_AC40dimensionsandweight.png.1f824f4ef310dc0542022c1af014500e.png
That's quitte vague but exact in the same sentence.
The AC 45 and 50's by Larry are one design classes in many aspects.
This has the same approach.
Most mysterious is the LEQ12 yacht:
1473387991_LEQ12.png.580d8f8bb411f4de5a29ba897911472e.png
Implying towing test are allowed.
 

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@t_huebs You may well be right. However its the only explanation I can see for the change in box size - the foil shape you posted would have fit in the old box for example. That and the fact that I can't make the RM calculations add up without something like it.

Time will tell

@SchakelTow tests are allowed. And given that you are allowed 4 foils on an LEQ12 I think that is one reason why they will be essential

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Or is the change of box size to allow a big enough curvature for a bi plane foil, adding foil length and tunneling effect between both planes + when lifted part of the foil comes out of the water and reduce drag. The stress in the curvature? Let's leave that aside, it doesn't matter on SA...

Joke aside, it will be interesting to see where they will head and performance difference across wind range with v2.

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16 hours ago, enigmatically2 said:

@t_huebs You may well be right. However its the only explanation I can see for the change in box size - the foil shape you posted would have fit in the old box for example. That and the fact that I can't make the RM calculations add up without something like it.

Time will tell

@SchakelTow tests are allowed. And given that you are allowed 4 foils on an LEQ12 I think that is one reason why they will be essential

Strange, I have seen foil testing in a towing tank and it's been done foil by foil.
Anyway towing tank test technology is something better discussed in a laboratory where it belongs.

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5 hours ago, Schakel said:

Strange, I have seen foil testing in a towing tank and it's been done foil by foil.
Anyway towing tank test technology is something better discussed in a laboratory where it belongs.

The rules prohibit tank testing. And limit the foils that can be rested on an L12, AC 40 or Ac75. And that's the only type of testing you can do

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11 hours ago, Stingray~ said:

Could we see swept-rake foil tips, given the new box?

There is nothing in the rule to prevent it, but then nor was there last time. So I suspect not. But it I have little more than that.

Swept-rake would give more stability but more drag for the same lift I think. 

Not sure how balance will be effected by the mass changes either. Plainly the loss of the bowsprit will move the CofG aft, not so sure about the other changes

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50 minutes ago, enigmatically2 said:

There is nothing in the rule to prevent it, but then nor was there last time. So I suspect not. But it I have little more than that.

Swept-rake would give more stability but more drag for the same lift I think. 

Not sure how balance will be effected by the mass changes either. Plainly the loss of the bowsprit will move the CofG aft, not so sure about the other changes

How much would the bowsprit really affect the CoG itself? Sure it is on the extreme end of the object in question but is not much mass. The whole package is losing weight significantly, so it is one of many things changing (going from 11 to 8 crew for instance will move things backwards too, unless you take the middle guys out).

I would think the CoG is a design input, you find the sweetspot and move things around where possible (ie. battery packs, hydraulic motors, grinding stations)

 

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6 minutes ago, shebeen said:

How much would the bowsprit really affect the CoG itself? Sure it is on the extreme end of the object in question but is not much mass. The whole package is losing weight significantly, so it is one of many things changing (going from 11 to 8 crew for instance will move things backwards too, unless you take the middle guys out).

I would think the CoG is a design input, you find the sweetspot and move things around where possible (ie. battery packs, hydraulic motors, grinding stations)

 

Yes and no. Of course you can move it to some extent. But you will (I would think) want to localise the weight near the CofG of the hull to minimise angular momentum. Given the other constraints I doubt you have too much ability to control the CofG.

The bowsprit may not make make much difference (though having been so far forward it will be disproportionate), but as I say its the only change where the impact is fairly obvious

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1 hour ago, enigmatically2 said:

Yes and no. Of course you can move it to some extent. But you will (I would think) want to localise the weight near the CofG of the hull to minimise angular momentum. Given the other constraints I doubt you have too much ability to control the CofG.

The bowsprit may not make make much difference (though having been so far forward it will be disproportionate), but as I say its the only change where the impact is fairly obvious

I was under the impression that weight had been significantly reduced for V2, most of it is crew (and guest) and the code zero itself, with media equipment increasing actually.

image.png.1f5ca880aa27258dada00a27084fd6bb.png

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10 minutes ago, shebeen said:

I was under the impression that weight had been significantly reduced for V2, most of it is crew (and guest) and the code zero itself, with media equipment increasing actually.

image.png.1f5ca880aa27258dada00a27084fd6bb.png

You are looking at a very old version of the rule for AC 36. The final weights were much different from what you show here, and tell a very different story. The max sailing weight in v.1.28 of the rule as used in the Match for AC 36 was 7834 kg, vs. 6940 kg for the draft version of the new rule.

Note that weights historically have suffered from a certain amount of mission creep in a new class. It is entirely possible that the weights in the draft version of v.2 may not represent the weights we will see in the final published version.

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6 minutes ago, accnick said:

 

Note that weights historically have suffered from a certain amount of mission creep in a new class. It is entirely possible that the weights in the draft version of v.2 may not represent the weights we will see in the final published version.

Hopefully with it only being a small adaptation of the previous rule, not so much

 

The more I think about it, the biggest disappointment is that they have not opened up more potential to reduce cavitation. Although I postulated the aeration solution I am not convinced that it is viable with the rules as they are (hope it is). They haven't allowed better surfaces. I say that because whilst improving light air performance is great, it would be nice to see that top end increased. Unless of course none of them were hitting cavitation speeds - I don't recall any hard evidence that they were

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15 hours ago, accnick said:

You are looking at a very old version of the rule for AC 36. The final weights were much different from what you show here, and tell a very different story. The max sailing weight in v.1.28 of the rule as used in the Match for AC 36 was 7834 kg, vs. 6940 kg for the draft version of the new rule.

Note that weights historically have suffered from a certain amount of mission creep in a new class. It is entirely possible that the weights in the draft version of v.2 may not represent the weights we will see in the final published version.

My mistake, thanks for pointing it out

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1 hour ago, Stingray~ said:

Some of the weight ‘mission’ creep was due to the redesigned foil arms. 

ah. but we are not back to the beginning now then if V1.0 is a similar weight to V2.0?

I'm not sure if this is interetsing enough for me to go through all the version numbers

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1 minute ago, shebeen said:

ah. but we are not back to the beginning now then if V1.0 is a similar weight to V2.0?

I'm not sure if this is interetsing enough for me to go through all the version numbers

Not really, because the lessons from that have been learned and the sticks are full strength. The weight has been saved elsewhere in things that they shouldn't have got wrong

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15 minutes ago, enigmatically2 said:

Not really, because the lessons from that have been learned and the sticks are full strength. The weight has been saved elsewhere in things that they shouldn't have got wrong

The final foil weight range in the Rule for AC 35 (v.1.28) was 1378-1385 kg each.

The proposed foil weight range in Draft 2A of the rule for AC 37 is 1265-1270 kg each.

Somehow, they's pulled 113-115 kg out of each foil. Maybe the new foil wing box gives enough opportunity to generate more righting moment that they can save weight.

Or maybe it's something else entirely.

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4 minutes ago, accnick said:

The final foil weight range in the Rule for AC 35 (v.1.28) was 1378-1385 kg each.

The proposed foil weight range in Draft 2A of the rule for AC 37 is 1265-1270 kg each.

Somehow, they's pulled 113-115 kg out of each foil. Maybe the new foil wing box gives enough opportunity to generate more righting moment that they can save weight.

Or maybe it's something else entirely.

Tangential to that possibility, here's a snap from the (beautifully produced) new Ineos video.

image.thumb.png.24c3e5deffcb254332ce6242d4935e17.png

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@accnickOh I agree that but us a risk, but it's a risk on each competitor not on OD components. So I doubt it will change. But it is one of the factors why I raised the possibility of a foil breakage:

Longer 

Lower chord length or thickness if they want to keep drag the same 

Lighter 

New restrictions on use of high strength materials.

It has to be a distinct possibility. But I doubt the rule and thus mass will change, as it is within each team's gift to resolve. Unlike last times problems

 

 

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It will be interesting to see if the teams will be using winglets.

In aviation they usually show up on planes with a limited wingspan to maximize aerodynamic efficiency, i.e. getting cleaner wing tip vortexes and providing a little more extra lift by fencing the laminar flow at the outer end of the wing. Examples would be passenger planes or thermal gliders.

Planes that are purpose built for performance like areobatic or fighter planes rarely use winglets - the wings of those a being designed to work within the needed performance envelope with as little drag as possible.

So, while the new box rule seems to invite the use of winglets I tend to expect mostly straight and sleek designs.

 

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18 minutes ago, Grog said:

It will be interesting to see if the teams will be using winglets

So, while the new box rule seems to invite the use of winglets I tend to expect mostly straight and sleek designs.

 

Remember that in this case the wingspan is limited by the rule so it does fit the cadres where you say it is used, certainly in AC36 they all used the max wingspan and their is little doubt they would have gone further if allowed. And that it may improve RM as well as efficiency

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2 hours ago, Stingray~ said:

Did the minimum span for the rudder stabilizers change? That came up with Brit on Friday momentarily but I forget the detail.

 

I suspect you are talking about this rule, which is new:

14.8        With the rudder centre plane aligned with LCP, there must be an achievable rake angle 
at which the lowest 0.500 m of the rudder, when projected to MWP, has an area of at least 0.300 m2.

This sets a minimum projected rudder area of the lower 500mm of the rudder relative to MWP. There is no specific minimum span. There is an effective maximum span, which is the same wording in the old and new rules:

14.7        At all yaw and rake angles that can be achieved, no wetted part of the rudder shall 
extend further outboard than planes offset from LCP by 1.500 m both to port and to starboard.
 

 

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On 1/12/2022 at 5:24 PM, NeedAClew said:

Is the FCS going to work out of the box this time?

The real question is: Did Ben finally get access to the FCS code so his team could look it over and fix it? Or is GD still hiding it from him.

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17 minutes ago, atwinda said:

The real question is: Did Ben finally get access to the FCS code so his team could look it over and fix it? Or is GD still hiding it from him.

They were just "holding it wrong"

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On 1/20/2022 at 10:21 AM, rh3000 said:

They were just "holding it wrong"

Prolly holding their mouths wrong too, I shouldn't wonder. ;-)

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43 minutes ago, Sailbydate said:

Prolly holding their mouths wrong too, I shouldn't wonder. ;-)

they were attempting to jack the boat up with the FCS , it was not designed for that

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  • 3 weeks later...

In a (hopeful? desperate?) attempt to get back to discussing something of relevance without rancour: where do we think the gains are going to be from Ac36 to AC37?

Clearly we expect the boats to lift out at much lower wind speeds but I very much doubt anyone turning uo with a boat that couldn't comfortably beat any of the AC36 challengers in medium airs will win overall.

However, a comment from one of the interviews shown recently (the British ex-F1 aerodynamicist I think) said that the last iteration were doing 53kts in 18kts of wind (presumably at the bear-away). That does suggest that downwind they are pretty close to the cavitation limit. At least a couple of the bear-aways it looked like some boats hit that limit and it caused problems.

So do we think they will be looking to raise that max cavitation limit? I doubt it would be worth it with any fixed aspect of design, so the only way would be some sort of device that allowed pressure reduction at speed. Still not convinced that will be achievable/worth it within the rules

Where else?

Upwind speed?

Tacking/Gybing angles? 

Speed through tacks & gybes?

Any thoughts?

 

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  • 2 months later...

how far off from AC37 boat launches are we?

 

Have any teams started building their hulls for V2, or are they still playing computer games? The ETNZ build crew appear to be busy with other stuff that doesn't float so i guess they will not be on the water anytime soon.

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Jack Griffin has a nice little overview of the AC75 V2 in the May issue of Seahorse Magazine. It's a summary for those of us too lazy to study the protocol. Some points being...

  • 68 ft long
  • Self tacing jib, no jib winches
  • No code zero or sprit
  • Sprit replaced with OD instrument wand (to keep 75' length)
  • No runners, no runner winches
  • Longer wingspan
  • Feedback and coupling of controls allowed
  • Ballast removed from foils (self righting rule - gone)
  • Four cyclors and four crew (2 driver/flight controllers, one mainsail trimmer, one tactician)
  • Mainsai and jib trim can be coupled
  • Active mainsail controls 1.5m above maststep or less. No more active controls up top
  • One ton lighter, 4 to 4.5m wingspan = able to lift off at lower wind limit
  • Cost? Well let's not go there

Peace out, and thanks Seahorse!

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On 4/20/2022 at 4:06 PM, bag dad said:

I would hazard a guess of 1.5-2 years

from today? so April 2024 for a August-Sep 2024 cup?

my guess would be launches from June 2023. gives you full year to play around with the stuff attached to the hulls which is more importanter

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