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      Abbreviated rules   07/28/2017

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pacice

Foiling Monohull - what would it look like?

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Do you think, TC, they will continue to let there be the possibility of a fatality or will Goobs just shorten his trapeze so it is not possible?

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19 minutes ago, Kiwing said:

Old, that was almost 3 years ago.

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10 hours ago, Boybland said:

I just can't get over how butt ugly they actually are! Seriously what is with the stubby floats and the weird rocker on the main hull! 

Sure ain't pretty.

Stubby floats is because they're supposed to foil not lean on them, yet they do lean on them quite a bit before the foils get enough lift which is one of my concerns about the absence in the JC75.

Its also pretty ugly how the need for dihedral between hull & floats causes the foils to be really long.

They really seem to be a huge handful, absolutely massive hits from handling error/running into a hole, spend a lot of time hunting/building apparent.

 

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10 hours ago, Boybland said:

As much as I actually really do enjoy watching the Super Foilers

I just can't get over how butt ugly they actually are! Seriously what is with the stubby floats and the weird rocker on the main hull!  I am sure there are performance reasons for all of it, but they are not exactly graceful!

i chatted to some people down in busso and they said that the floats are shaped like that with the ridges on the bottom to prevent pitchpoles, they said that they took the idea kinda from seaplanes, although it does not stop bad pitchpoles

sorry i did not post this earlier, must have forgotten to press submit hahaha

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1 hour ago, Kiwing said:

Do you think, TC, they will continue to let there be the possibility of a fatality or will Goobs just shorten his trapeze so it is not possible?

checking out the boats there, it looks like more and more of the boats are opting for a cat style trap system with a fixed height and lacki takeup

it would seem that it could be safer to prevent any dejavu, although iain still has the skiff style setup

really, the adjustment shouldn't be all that important seeing as they have a rough sliding splice and the difference in force that they would be applying from changing heights is so minimal due to the size and power of the boats compared to boats that run a cleat on the trap like 49ers and other skiffs

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9 hours ago, Kiwing said:

Do you think, TC, they will continue to let there be the possibility of a fatality or will Goobs just shorten his trapeze so it is not possible?

I agree with enibriated, they will keep trapeze with shorter lines and give them some protections, ....until something serious happens. The boat seems pretty dangerous, fast, instable, whith long razor sharp surfaces.

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Foils designed for less than 50kts do not have sharp leading edges. The tips get thin but not sharp. You will get serious brusing from leading edge impact but not deep cuts. Trailing edges are very sharp, moth sailors get cuts just handling them, but impact from crashing does not happen. Broken carbon is also very sharp, and needs to be avoided if stuff gets broken. The superfoiler foils I have seen look pretty blunt.

 

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1 hour ago, Phil S said:

Foils designed for less than 50kts do not have sharp leading edges. The tips get thin but not sharp. You will get serious brusing from leading edge impact but not deep cuts. Trailing edges are very sharp, moth sailors get cuts just handling them, but impact from crashing does not happen. Broken carbon is also very sharp, and needs to be avoided if stuff gets broken. The superfoiler foils I have seen look pretty blunt.

 

yeah, leading edges on them are not sharp at all

the trailing edges are nothing compared to some moth foils either

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18 hours ago, Phil S said:

Foils designed for less than 50kts do not have sharp leading edges. The tips get thin but not sharp. You will get serious brusing from leading edge impact but not deep cuts. Trailing edges are very sharp, moth sailors get cuts just handling them, but impact from crashing does not happen. Broken carbon is also very sharp, and needs to be avoided if stuff gets broken. The superfoiler foils I have seen look pretty blunt.

 

Pardon me, but if I remember correctly, a woman´s leg was cut off by a foil from Spindrift. I guess that at 20 knots any foil can produce a severe cut, IMHO

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The lady was injured by Spindrift's rudder not a hydrofoil from memory. It may have been sharp or blunt but getting hit by such a heavy boat at such speed was never going to be good. People get limbs severed by motor cars too which are very blunt. 

 

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Actually Goobs was threatened by the rudder and its seemed very likely to me the situation could easily be repeated.

I hope I am wrong because the next sailor might not be so strong/skilled and with it.

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On 10/03/2018 at 12:21 PM, Tornado-Cat said:

It was a rudder at 20 kts. Sharp or not, a foil at 40kts could cut a body in half.

ca4072c32cf6a0ff07d41f11bda12ae9.jpg

Not to mention anything at 40 knots that is harder than the object it is hitting and attached to several tons of mass will just make a big ole mess regardless of whether it actually cuts anything, it would be about the same as being hit by a car!

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Yes exactly the same thing could happen if a foredeck hand went over the windward side of a ocean racing canting keeler, or even one with twin rudders. Not yet happenned but same consequences likely. Not just a foiling issue, not just an AC issue.

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24 minutes ago, Phil S said:

Yes exactly the same thing could happen if a foredeck hand went over the windward side of a ocean racing canting keeler, or even one with twin rudders. Not yet happenned but same consequences likely. Not just a foiling issue, not just an AC issue.

with the G-Force that these boats will be creating, there is a much higher chance of a foredeck hand going flying off in a last minute dodge of an opponent

this being said, they will only be using furling gennakers during light air, the G forces will be lowered and do you even need a foredeck hand to pull and unfurl a gennaker??

i'm sure it will be thought of by the rule makers between now and the cup though

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ETNZ was the first team to put a strop in front of the wing sail for a handhold when crossing the tramp in AC35 i believe.

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On 3/12/2018 at 5:00 PM, inebriated said:

with the G-Force that these boats will be creating, there is a much higher chance of a foredeck hand going flying off in a last minute dodge of an opponent

The crew will be in the boat and only need to move a few metres, not running across flat decks or tramps like the AC50s (or SuperFoilers). It's not like the foredeck crew will actually be on the foredeck, or crossing in front of the mast.

Though if someone does go over the side from in front of the main foils there's a very good chance they'll be hit by the foil or strut, more likely the foil. And it will not break away like a SuperFoiler rudder might.

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Risk to sailors isn't the biggest issue I have with the JC75, its the restrictions that will have to be implemented during racing thats the main issue for me.  Based on animations the foils will be, roughly, 6-10 feet in the air and extend past the edge of the boat by another 3 to 6 feet?  So that means rules will have to be established to prevent boats from coming to close to each other to prevent foils from impacting people, obviously, but also from impacting the other boat (specifically the rigging).  So say goodbye to pre-start action and say hello to marginal on the water umpire calls when one boat penetrates the other boats protective halo.  Or am I way off base?

WetHog  :ph34r:

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3 hours ago, WetHog said:

rules will have to be established to prevent boats from coming to close to each other

 

The has already been addressed - just as it was in AC35.

An outline (the protective halo ;)) was decided upon by the umpires that described the zone around the AC45s and the AC50s into which you could not intrude without incurring a penalty - regardless whether actual contact was made.

The plan is to implement exactly the same thing again, just with a different shape this time, a diamond. Simple.

Calls on 'diamond to diamond' contact will typically be made off the water as in AC35, not by marginal on the water umpire calls

Joust away!

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4 hours ago, Meatbomb said:

That must have been a pretty skinny halo from some of the luffs I saw.

This and how far a retracted frog leg foil extends away from the side of the boat will be a major factor.  The halo would have to be extended significantly to ensure a retracted frog leg doesn't come in contact with crew or rigging.  Like a 30 to 40 ft diameter halo from the center of the boat, or more?  

WetHog  :ph34r:

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I guess the UI will be like a reversing sensor: a string of lights and beeper. The closer you get, the more lights and faster the beep until a solid beep means "do your penalty".

No need for umpires, if computers can run simulations as accurately as has been claimed, they should be able to make rule decisions with far greater precision than humans. They should also be able to give evasive action advice to ensure no contact, so the infringed boat doesn't have to push it to make the breach obvious.

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On 3/13/2018 at 7:03 PM, nav said:

The has already been addressed - just as it was in AC35.

An outline (the protective halo ;)) was decided upon by the umpires that described the zone around the AC45s and the AC50s into which you could not intrude without incurring a penalty - regardless whether actual contact was made.

The plan is to implement exactly the same thing again, just with a different shape this time, a diamond. Simple.

Calls on 'diamond to diamond' contact will typically be made off the water as in AC35, not by marginal on the water umpire calls

Joust away!

 

15 hours ago, Tornado-Cat said:

:lol:

 

And why do you think luffing duels will happen, mainly if the diamond is big enough to prevent a boat from covering the other one ? Fantasy of another century ?

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40 minutes ago, nav said:

 

 

How the hell did you pull that last quote up from infamously deleted thread ?

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Nice to see my hypothesis shared - that initially (low speed) the leeward foil will be kept in the vertical/docking position and act as a conventional ballasted keel. It will be canted out when speed is high enough (about 7 kts, I guess) to at least support its own weight.

But Jean Sans repeats the usual fallacy: an AC75 may well keep foiling with 9 kts TWS, but no way it'll be able to take off with that wind

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12 hours ago, Xlot said:

Nice to see my hypothesis shared - that initially (low speed) the leeward foil will be kept in the vertical/docking position and act as a conventional ballasted keel. It will be canted out when speed is high enough (about 7 kts, I guess) to at least support its own weight.

But Jean Sans repeats the usual fallacy: an AC75 may well keep foiling with 9 kts TWS, but no way it'll be able to take off with that wind

I dunno,

Don't Comanche and other high performance monos do something like 1.25 to 1.5 times windspeed in lighter conditions (just going from what I have read)? If they can match or better they then 9 to 10 knots TWS liftoff wouldn't seem implausible on a beam reach, then either turn up or down depending on where your trying to go.

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14 hours ago, Xlot said:

Nice to see my hypothesis shared - that initially (low speed) the leeward foil will be kept in the vertical/docking position and act as a conventional ballasted keel. It will be canted out when speed is high enough (about 7 kts, I guess) to at least support its own weight.

But it's extremely unlikely they'll race at such speeds. While in the docking position, if the foil produces any lift at all, there will be a significant vector to leeward unless the foils can be trimmed for zero lift and minimum drag simultaneously. However it doesn't seem sensible to design for that scenario given the likely tradeoff in other areas and very low chance it will occur in racing.

14 hours ago, Xlot said:

But Jean Sans repeats the usual fallacy: an AC75 may well keep foiling with 9 kts TWS, but no way it'll be able to take off with that wind

Where's the fallacy? 9kns TWS might have variations of perhaps ±3kn. I think the point is that if they can get foiling in a puff of say 11 or 12kn, they may be able to sustain it.

 

 

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4 hours ago, RobG said:

But it's extremely unlikely they'll race at such speeds. While in the docking position, if the foil produces any lift at all, there will be a significant vector to leeward unless the foils can be trimmed for zero lift and minimum drag simultaneously. However it doesn't seem sensible to design for that scenario given the likely tradeoff in other areas and very low chance it will occur in racing.

18 hours ago, Xlot said:

leeward foil partially raised to resist leeway and be in position for maximum righting moment? windward foil at 90 degrees just above water to provide least drag and maximum righting moment? foils close to final position for takeoff?

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19 hours ago, RobG said:

But it's extremely unlikely they'll race at such speeds. While in the docking position, if the foil produces any lift at all, there will be a significant vector to leeward unless the foils can be trimmed for zero lift and minimum drag simultaneously. However it doesn't seem sensible to design for that scenario given the likely tradeoff in other areas and very low chance it will occur in racing.

 

I'm thinking the leeward wing will never be canted inward past horizontal, and will quickly need to be rotated outboard as speed - and in parallel, apparent wind/heeling moment - increase. In fact, I'm thinking that this outboard rotation will need to happen as the boat lifts free of the water surface, since you will  instantly need a lower vertical Cl, and more righting moment at the crossover point.

You can map the vectors at various positions - knowing that the vertical lift = boat all up weight, and the lift generated by the wing (ignoring flaps for the moment) increases with the square of speed, you can see that you will very quickly to cant the wing to it's maximum outboard position. As an aside, extreme cant angles are a huge part of why the kite foilers are so fast, and this is why the designers are talking about top speed potential equal to or greater than the first generation AC50s. 

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12 hours ago, surfsailor said:

As an aside, extreme cant angles are a huge part of why the kite foilers are so fast, and this is why the designers are talking about top speed potential equal to or greater than the first generation AC50s. 

 

Agreee, but with the given AC75 geometry the outboard tip will very quickly break the surface or ventilate - unless a fairly dramatic negative dihedral is adopted, as in the BAR renderings

In this connection, I'm reminded of nav's (?) smart comment that flaps must have the same rotation range, but not necessarily the same deployment law ...

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On 11/4/2018 at 4:07 AM, RobG said:

But it's extremely unlikely they'll race at such speeds. While in the docking position, if the foil produces any lift at all, there will be a significant vector to leeward unless the foils can be trimmed for zero lift and minimum drag simultaneously. However it doesn't seem sensible to design for that scenario given the likely tradeoff in other areas and very low chance it will occur in racing.

Not thinking about racing, but accelerating out of a dial-up (that's what they said thay wanted, right?)

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On 11/4/2018 at 1:44 AM, Boybland said:

I dunno,

Don't Comanche and other high performance monos do something like 1.25 to 1.5 times windspeed in lighter conditions (just going from what I have read)? If they can match or better they then 9 to 10 knots TWS liftoff wouldn't seem implausible on a beam reach, then either turn up or down depending on where your trying to go.

Agree it's the likely scenario, also because it makes momentarily unloading the leeward foil much easier - this should lower take-off speed by the square root of 2

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8 hours ago, Xlot said:

 

Agreee, but with the given AC75 geometry the outboard tip will very quickly break the surface or ventilate - unless a fairly dramatic negative dihedral is adopted, as in the BAR renderings

In this connection, I'm reminded of nav's (?) smart comment that flaps must have the same rotation range, but not necessarily the same deployment law ...

The rule allows a wide range of of wing geometries, including massive anhedral - but that has not turned out to be the fastest solution in kites. A better approach (IMO) would be exploring  surface piercing tip geometries (look at ETNZ's high wind foils from AC35) and/or fences to arrest ventilation.

 

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  ^ Foils must be symmetrical, so fences would have to be (unnecessarily) duplicated on the inside. Guess there's a drag penalty

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^ Sure, everything is a trade off. But the price of sudden ventilation would very high, and - if small fences really worked - you could potentially use a flatter (less anhedral)more efficient  (faster) wing, since the risk of surface piercing would no longer be a design constraint. I think surface piercing is inevitable in any case, since T foils don't have the same leeway coupling characteristics of the L foils used in the last 2 cup cycles.

 

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10 hours ago, surfsailor said:

The rule allows a wide range of of wing geometries, including massive anhedral - but that has not turned out to be the fastest solution in kites. A better approach (IMO) would be exploring  surface piercing tip geometries (look at ETNZ's high wind foils from AC35) and/or fences to arrest ventilation.

 

did you see surface piercing behaviour from ETNZ's high speed foils? Link please?

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I never specifically saw it on ETNZ (talking high wind foils), but Macif 17 has very similar tip geometry on the ama foils, and I saw lots of footage where the tip was piercing the surface during steady state flight. We looked at doing a similar treatment (reverse scimitar tip planform) on kite foils, but it just looked too dangerous - like a carbon fiber fish hook. But I’m pretty confident that geometry mitigates ventilation down the foil blade.

Here’s a pic of Macif 17 - you can clearly see the foil tip :

 

33818AA2-18D9-4D00-BF85-F5FDEEA7C0F3.jpeg

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Just now, surfsailor said:

I never specifically saw it on ETNZ (talking high wind foils), but Macif 17 has very similar tip geometry on the ama foils, and I saw lots of footage where the tip was piercing the surface during steady state flight. We looked at doing a similar treatment (reverse scimitar tip planform) on kite foils, but it just looked too dangerous - like a carbon fiber fish hook. But I’m pretty confident that geometry mitigates ventilation down the foil blade.

Here’s a pic of Macif 17 - you can clearly see the foil tip :

 

33818AA2-18D9-4D00-BF85-F5FDEEA7C0F3.jpeg

i find it very hard to believe that they used surface piercing foils

macif 17 would of had them for stability, just as the ac72's did

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^ I’m not suggesting that the foils on ETNZ were designed to pierce the surface when functioning normally. I’m saying that - in the event of a surface pierce - the tip geometry is designed to mitigate ventilation so there is not a catastrophic wipe out. The kite foils - which have similar extreme cant angles to the spider monkey - also have issues with this.

ETNZs light wind foils had different tips from what I could tell.

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On 4/13/2018 at 7:09 AM, surfsailor said:

The rule allows a wide range of of wing geometries, including massive anhedral - but that has not turned out to be the fastest solution in kites. A better approach (IMO) would be exploring  surface piercing tip geometries (look at ETNZ's high wind foils from AC35) and/or fences to arrest ventilation.

 

So ETNZ never used a surface piercing foil in AC35,  we all know this except you and shhhh(doug lord).

backpedal for 5 posts please.

i submit the dihedral on the foil tip was to provide upwind lift above what cant could angle the foil. Much as in way the kiters achieve with a horizontal windward board angle.

edit: the oh-no...up-tip section provided lift canted horizontal whilst the angle up to the tip provided lift upwind.

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This pic shows the extreme cant used on the low speed "bat-wings". Without drawing yellow lines it looks like the tip would be horizontal in the water.

I suggest that if ride height increases, the first foil segment would start to ventilate, decreasing lee resistance and providing lee coupling; and decreasing lift, kind of like a reverse J-foil surface piercing effect.

 

headonbatwings.jpg

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^ The low wind foil is all about early lift and sustained flight in marginal conditions and through maneuvers . The high wind foil is all about maximizing L/D in powered conditions, and control. The tip geometries are very different. 

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3 hours ago, barfy said:

Without drawing yellow lines it looks like the tip would be horizontal in the water.

Thats the conclusion of most of us other than Drug®Lord©

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23 hours ago, surfsailor said:

^ The low wind foil is all about early lift and sustained flight in marginal conditions and through maneuvers . The high wind foil is all about maximizing L/D in powered conditions, and control. The tip geometries are very different. 

tell me more about the tip piercing.

please comment on the angle of of the foil between tip and daggerboard?

ETNZ's craft was optimized for upwind sailing and their polars showed huge lift when they wanted to use it.

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10 hours ago, barfy said:

tell me more about the tip piercing.

please comment on the angle of of the foil between tip and daggerboard?

ETNZ's craft was optimized for upwind sailing and their polars showed huge lift when they wanted to use it.

Of course ETNZ's light wind foils were designed for huge lift - but I wasn't talking about those. My suggestion was simply that using wingtips like ETNZ's high wind foils (and Macif 17 and Maserati) would be an alternative approach to mitigating ventilation to anhedral and/or ventilation fences. 

Instead of trying to be intentionally obtuse - including posting pictures of the lightwind foils, which were completely different - why don't you look at the pictures I posted of ETNZs high wind foils. The wingtip design is very similar to that of Macif 17 (and Maserati), both of which are surface piercing. The inboard leg the AC50 foils (on all the boats) was at least horizontal if not beyond that with windward heel. But at very high speeds in powered up conditions which assumes increased surface texture etc - regardless of whether the tip actually pierces the surface - a foil operating near the surface has increased ventilation risk since the trailing tip vortex provides a potential airpath, and obviously generating huge lift is not as much of a design criteria. Hence the design of ETNZ's high wind foil tips.  Here's a video showing what I mean about tip votices turning into ventilation:

 

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On 4/12/2018 at 9:09 PM, surfsailor said:

 A better approach (IMO) would be exploring surface piercing tip geometries (look at ETNZ's high wind foils from AC35) and/or fences to arrest ventilation.

 

On 4/13/2018 at 9:51 AM, surfsailor said:

This is the ETNZ foil I’m referring to:

 

149B57E7-280E-45EF-9D92-C857C5062F64.jpeg

Is it your opinion that the key factor in this ^ foils design is to mitigate the type of ventilation show in the video above?

If so what leads you to that conclusion when there are so many other factors that may have been considered equally or more critical by the foils designers.

And again if you consider it the most important criteria why would it have been any less of a concern in their other foil sets?

Why do you refer to these foils as having surface piercing tip geometries

You have mentioned the importance of windward cant to the high functioning of kite-foiler foils, since this aspect is much more constrained in other platforms how much relevance do you consider they and their designs have to other classes?

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^ You need to separate the foil tip from the rest of the wing. Total span was constrained by the AC 50 rule because the foils in their entirety had to fit into a circle.  So the lightwind foils use that full span to generate as much lift as possible, although I know some (if not all) were designed with washout towards the inboard tip so that as the foils AoA was reduced (as speed increased), the center of lift would move outboard, which in turn would increase the righting moment. But the main goal was to get up on the foils as early as possible and stay there. ETNZ's design was by far the best at this, plus had a very wide range, but was extremely unstable so only possible with the dedicated flight controller following computer instructions to very accurately control ride height etc.

On the high wind foils, with more available horsepower from the wing, you can start to use some of that span (which as I noted was limited by the rule) to seriously reduce drag even at expense of total available lift, and you can also focus on things like control. You would also want to make the wing more stable even with computer controlled flight since all of the boundary conditions (water surface texture, wind dynamics) are more chaotic. That extremely pointed small surface area wingtip on the foil pics I posted is not generating much lift. It's mitigating tip vortices and ventilation.

I referred to the wingtips on ETNZ's high wind foils as having 'surface piercing geometries' because the two other places I've seen that tip design were on Macif 17 and Maserati, on their surface piercing ama foils. Those designs predate the ETNZ foils. So that's how I think of that geometry - sorry this is so difficult for you and barfy to grasp.

Up until the AC75s, the kite foils with their extreme cant have been an outlier with regards to everything else that is going on in foiling. L foils, for example, have the 'mast' outboard, the horizontal lifting surfaces extending inboard, and benefit from leeway coupling - as the boat rises, it's lateral resistance (a product of how much of the vertical part of the foil is immersed) is reduced, so it can sideslip and unload the rig etc. But the giant spider arms on the AC75 basically put the foils in the exact same position relative to the water as the kites - so all of a sudden, kite foil designs become more relevant. 

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yup, sorry to confuse by posting pics of the low speed foils, which were a more pronounced J shape but which were never seen in a configuration where the tip would pierce the surface.

Your video is interesting, as are the pictures of the high speed foils, (i think MIHBDA shot those).

You have shown a picture of a large tri sporting obvious J foils ala AC34. Maybe post some pics of a surface piercing foil along with ETNZ's hi speed foils to bolster your case that they were designed alike.

I found this shot of ETNZ AC35 on high speed gear, not the best angle for yellow lines, but carrying so much outboard cant i would think the tip is well horizontal. 

The tip vortex in your video was not developed from a tip that was anywhere near the surface, and tip vortexes on ETNZ's foils may well have been "gated" from cavitating the entire foil by the crazy profiles going on evident in that lovely picture? Have to ask someone that knows.

Your new assertion that the angles of the AC36 wings will be quite alike the cant that kiters can develop is true. But Kite Foilers don't use surface piercing geometries either.

 

hispeedfoils.jpg

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27 minutes ago, barfy said:

 

Your new assertion that the angles of the AC36 wings will be quite alike the cant that kiters can develop is true. But Kite Foilers don't use surface piercing geometries either.

 

 

Have you looked at the renderings of the AC75s? They look like kite foils, albeit with the addition of flaps. 

As kite foil masts become longer (110 cm plus), the more extreme angles of cant that result make foil tip treatment ever more critical, and we are definitely looking at surface piercing as one way of mitigating excess lift and excess lateral resistance at the same time when going downwind. Downwind control at speed is currently an issue - the same things that make the kites crazy fast upwind (huge lateral lift) are a liability going the other direction. Controlled surface piercing would allow us to shed lifting surface area. As I noted earlier, we've looked at ETNZ high wind/Macif 17/Maserati type wing tips, but haven't pursued it (yet) due to their resemblance to carbon fiber fish hooks. Actually, they look more like filleting knives, but you get the idea.

The flaps will increase the range of the wings by allowing the lift coefficient to be modified, so maybe not an issue. But still, we are talking about wings that need to have a functional speed range of 15 - 45 kts (or more).

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yes, the renderings do have reverse camber. What comes out of the designers remains to be seen. There is a large design box.

Ha, that will be fun watch the kiters blowing tips out of the water at speed. a bit scary tho as you say.

The wide range of the wings/flaps will be key for dev. I heard whispers of ETNZ top speed early on way above what we saw on the course, I imagine the lift-off speed was too high, or the lee resistance wasn't there. With flaps there may be some serious boundaries pushed, I don't imagine many Moth devs have the deep pocket, hydro designers, and sims that will be put to bear on this problem.

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41 minutes ago, hoom said:

Found this in youtube recommended list lol

 

i think these people have spent too much time thinking whether they could rather than whether they should...

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On 16/4/2018 at 12:00 AM, surfsailor said:

Actually, they look more like filleting knives, but you get the idea.

 

Yecch!

 

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10 hours ago, Xlot said:

 

Yecch!

 

Tell me about it. We've been very lucky so far, but at some point - if we don't take steps now to mitigate some of the obvious risks - something really bad is going to happen. 

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On 16/04/2018 at 4:30 AM, surfsailor said:

Here's a video showing what I mean about tip votices turning into ventilation:

The video doesn't show that: ventilation starts at the surface and moves down, it doesn't start at the vortex of the (submerged) tip. A tip breaching the surface (or going very close) may induce ventilation, and vortexes may have an influence on that but that isn't what the video shows.

Moth main foil tips occasionally pierce the surface due to windward heel, it doesn't seem to induce ventilation (speeds around 15 kn I guess). 

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1 hour ago, RobG said:

The video doesn't show that: ventilation starts at the surface and moves down, it doesn't start at the vortex of the (submerged) tip. A tip breaching the surface (or going very close) may induce ventilation, and vortexes may have an influence on that but that isn't what the video shows.

Moth main foil tips occasionally pierce the surface due to windward heel, it doesn't seem to induce ventilation (speeds around 15 kn I guess). 

Ya, I phrased that wrong, you're right of course, and the video clearly states that. What I was looking at was way the tip vortex - even with the tip deeply submerged as in the video - provided an airpath for ventilation. Kite foils - with their extreme cant - put the upper wingtip very close to the surface (this will soon be common in windsurf foils as we push into higher performance) so in that orientation, that airpath can lead to full ventilation. It may not be an issue at 15 kts, but it can be pretty exciting at 30 plus.

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Didnt follow the hole tread - so maybe this was up before but; how fast are these foiling-arm working - from up to foiling - how long will it take? On the last two ACs they could dump a foil in 1-3 sec it seemed - these electric operated arms - will take muck more time - making fast maneuvers hard. And also falling off foiling will be catastropic in a race - not like the cats -that also lost some - but here it will take time to get back up in light conditions.

 

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Interesting video, but note that this is a foil being held at a constant incidence.  In reality, as boat speed climbs then the foil will ( or should be if the attitude control is there ) be working at increasingly lower lift coefficients, so the tendency to ventilation is reducing all the time.  

That's assuming we're in full flight mode of course, and so by the time the foil is breaking surface its more of a planing surface than an immersed foil behaving as an airfoil.   You can play games on the sections and sizes with this in mind and decide what is the best control solution for the boat in question.

 

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Interesting but as noted the early bubble stream begins down flow from the tip and is not connected at first so isn't this a result of the vortices, cavitation?  Does anyone know if the proposed twin swinging keels will even fly, any modeling yet?

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^ I am starting to think these are designed to compete both non foiling and foiling. So some race completely foiling winds above 15-19 knots and some races completely non foiling.  With only a few determined by the ability to fly early.

Very low wind speed, windward foil out of the water using it's weight for righting moment, lee foil immersed, hydrodynamic righting moment and lateral resistance.

High speed completely foiling all around the course as the video shows.

Mid range partly foiling.  The ability to foil early upwind will decide IMHO.

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I have had the ventilation/cavitation debate many times usually over rudders and propellors. It is a fine line when one ends and the other begins so I coined the term 'CAVILATION' to cover both phenomenom. 

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