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Why so nose up on foils - IMOCA

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This might be simple if its a rule issue, but why are these crazy machines doing wheelies?

Would a rudder foil make submarining off big seas way more likely?

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Rules don't allow for foils on rudder, thus they are like stool with 2 legs as they have been called. The third leg to have stability is the hull and it sails better with the back end in the water rather than the front end.

Current rules are believed to be a transition from non foiling to fully foiling in next gen rules and prevent too big performance gap between boat generation.

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The Olympic class Nacra 17 initially had no rudder foil just c- foils. I likened that to having a stiletto in the middle of your shoe. Rather difficult to balance on. 

I’m no mono man but when they fully foil the imocas etc you’d have to think that the traditional speed difference between mono and multi  (at this high end and in foiling conditions) will have pretty much gone. 

The AC 75’s look like they will be atleast as fast as the previous foiling multis. 

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Quote

why are these crazy machines doing wheelies?

This is an interesting development. The original DSS (Dynamic Stability System) foils were designed to lift the stern of the boat up. And as it lifted, the foil leveled out so the stern would not keep lifting further. Rather it would settle into a position.  That's why it was called Dynamic, because the lift changed as the boat was lifted.

So I too have been looking at the new foils and how they perform. 

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Btw, I guess your rules exclude another foil on the hull down near the back of the boat and have a normal (albeit longer) rudder? 

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46 minutes ago, LionIsland said:

.........I’m no mono man but when they fully foil the imocas etc you’d have to think that the traditional speed difference between mono and multi  (at this high end and in foiling conditions) will have pretty much gone. 

The AC 75’s look like they will be atleast as fast as the previous foiling multis. 

^^^^^^This. When foils are the only things in the water, the airborne hull configuration above is almost irrelevant other than weight and windage. IMOCAs still have a keel foil which isn’t efficient at providing vertical lift, but has a lot of drag, but the AC 75’s have solved that one, with each keel foil weighing pretty much the the same as  a cross beam and ama on a tri......

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3 hours ago, Lakrass said:

Rules don't allow for foils on rudder, thus they are like stool with 2 legs as they have been called. The third leg to have stability is the hull and it sails better with the back end in the water rather than the front end.

Current rules are believed to be a transition from non foiling to fully foiling in next gen rules and prevent too big performance gap between boat generation.

Hope they transition to T's on rudder soon. Supposedly the current situation leads to some pretty ugly motions due to lack of pitch stability. 

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1 hour ago, Sidecar said:

^^^^^^This. When foils are the only things in the water, the airborne hull configuration above is almost irrelevant other than weight and windage. IMOCAs still have a keel foil which isn’t efficient at providing vertical lift, but has a lot of drag, but the AC 75’s have solved that one, with each keel foil weighing pretty much the the same as  a cross beam and ama on a tri......

Yes. Well.  I haven’t quite figured out why the 75’s don’t fall over. Are they downloading the windward aileron/wing of the main foil enough  (which happens to be on the Lee side of the boat) and the rudder t-foil plus the crew weight on windward rail to foil but not fall over? Tricky. 

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But yes (re: foiling mono v foiling mono not withstanding the kooky 75’s) I s’pose the width of the multi still gives leverage and stability and, yes, you still got a keel n fin on the mono.

Not that it couldn’t be swung right out and aided with foils doesn’t even need to be in the water too. That can’t be much heavier than a full length float or two and all the windage and crap associated with two floats. 

I wanna see 10 years from now. Mad. 

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Fully foiling Mini pretty impressive. Nuts. Sleep would be a snitch.

Not. 

Sleep on anything high end in breeze these days would be impossible. Crazy shit. 

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1 hour ago, LionIsland said:

Yes. Well.  I haven’t quite figured out why the 75’s don’t fall over. Are they downloading the windward aileron/wing of the main foil enough  (which happens to be on the Lee side of the boat) and the rudder t-foil plus the crew weight on windward rail to foil but not fall over? Tricky. 

In AC 75’s the lifting leeward foil becomes the dynamic centre of buoyancy, as it does in foiling Moths for example, and that means that the entire weigh of boat and crew provide the righting moment. This is also further augmented by canting the windward foil further out to windward which also can adjust in and out to keep the boat balanced without the need for shifting crew or easing sails.

When there is less speed and they need both foils down, there is also less righting moment, so it all works in sync. In theory.

PS:

I expect, as soon as class rules allow, Minis and IMOCAs will also go down that path because it gets rid of some weight and one lot of foil drag and could provide potentially greater re-righting moment  for boats which have turtled.

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That’s some crazy shit, right there. 

But, Shirley, trying to apply that mad idea without a decent counter balancing weight, say the swinging keel,  (which, I suppose, can operate a little more “normally” in non foiling conditions) to an ocean going vessel is nigh on impossible. 

Or or maybe they can pump some water out there to the windward side contraption when needed. Weight when you need it, piss it off when you don’t. 

You’d think a canting rig would help dramatically too, wouldn’t you? 

Who knows what they’ll come up with? 

Foiling trimaran (or cat) is looking simple in comparison. 

 

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1 hour ago, LionIsland said:

......trying to apply that mad idea without a decent counter balancing weight, say the swinging keel,  (which, I suppose, can operate a little more “normally” in non foiling conditions) to an ocean going vessel is nigh on impossible........

You’d think a canting rig would help dramatically too, wouldn’t you?

Foiling trimaran (or cat) is looking simple in comparison

You forget that each set of foils are probably also a ballasted. To get those kind of thicknesses plus the strength and weight, they are probably something like solid tungsten. (SG: tungsten19.6 vs lead 11.3).

A canting rig would help, who says they haven’t got or won’t have them when they have mastered foiling the beasts?

I tend to agree that foiling multihulls look simpler to do......

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6 hours ago, Sidecar said:

^^^^^^This. When foils are the only things in the water, the airborne hull configuration above is almost irrelevant other than weight and windage. IMOCAs still have a keel foil which isn’t efficient at providing vertical lift, but has a lot of drag, but the AC 75’s have solved that one, with each keel foil weighing pretty much the the same as  a cross beam and ama on a tri......

I wouldn't be so sure about that.......

Keel fins are designed to go straight through the water, and will provide lift if they are not.

If you look at the nose up angle the boat is at when they are foiling, that means the keel fin is also at the same angle of attack upwards... and the bulb also, producing some amount of vertical lift.  not as much as the lifting foil, but it would be providing some kind of balance to the platform in either case, more of a tripod than a two legged chair balanced by the wind in the sails.

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True, but it is also a heeling moment, thereby reducing it’s overall value.......

PS:

I also understand that some canting keelers have their bulb CG’s sufficiently far in front of the keel to induce twist and a negative AoA to increase RM?

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2 hours ago, dachopper said:

I wouldn't be so sure about that.......

Keel fins are designed to go straight through the water, and will provide lift if they are not.

If you look at the nose up angle the boat is at when they are foiling, that means the keel fin is also at the same angle of attack upwards... and the bulb also, producing some amount of vertical lift.  not as much as the lifting foil, but it would be providing some kind of balance to the platform in either case, more of a tripod than a two legged chair balanced by the wind in the sails.

Not really, if you look in the Imoca thread for the last V&V Loriot Prevost interview, he explains that the keels have "tilt", that is the rotation axis is not exactly horizontal but goes up a bit (around 5°) and this to provide vertical lift when the keel is canted and the boat heeled. So that the keel fin provides vertical lift (but also some negative RM)

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9 minutes ago, Puntone said:

Michel Desjoyaux said : these boats are chairs with three feet

 

He said more "a three feet stool missing a feet" (rudder elevator)

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Theoretically it is possible to lift the stern up by using rudders but this is a bit draggy option with the current setup - both needs to look more outwards. The more it heels the more the upwind rudder needs to work with it tip as horizontal stabilizer. This drag can be reduced by making rudders longer with asymmetric profile and with higher angle between them. Like upside down airplane with V tail.

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9 hours ago, Sidecar said:

True, but it is also a heeling moment, thereby reducing it’s overall value.......

PS:

I also understand that some canting keelers have their bulb CG’s sufficiently far in front of the keel to induce twist and a negative AoA to increase RM?

Yeah, but the foiling boat doesn't need more righting moment.... it could benefit massively from any type of additional stability however. Who knows how it is setup, but I would guess from the pics, the keel fin is doing more than supporting the keel, and it's helping get the boat out of the water like a surface piercing foil but in reverse.

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From a friend:

IMOCA Lift.jpg

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At short, both keel and foil act like two real foils at both sides.

Similar shape of "shaft” of the both "foils”, like a wing. Therefore it generates lift upwards.

Of course the keel is the stiff one and the foil (also other factors as  sails settings, trim) has to adapt to it for the least drag for both "shafts" in ride..

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Yes I can also see that the keel foil lift is self regulating in that it’s overall heeling lift reduces with increased heel because of foil area loss whilst static righting moment increases, until you reach the point where there is insufficient total upward lift and you have splashdown?

There is obviously an optimum heel range for max foil lift, and the name of the game is to get the boat to that heel ASAP and keep it there ALAP.... Which is why they tend to sail pretty erratic courses, because it is easier and faster to head up or bear away rather that to sail trim.

I wonder if they have a algorithm in their autopilots which also responds to heel?

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13 hours ago, Doug Lord said:

From a friend:

IMOCA Lift.jpg

Depends which boat you talk about I guess.   HB has a curved foil, and I very much doubt that it has lift vectors like that on the HB foil. They go vertically up - not sideways.

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12 hours ago, Sidecar said:

I wonder if they have a algorithm in their autopilots which also responds to heel?

Some teams are actually using Madintec autopilot (e.g. Initiative coeur) " First 3D autopilot on the market".

I think it uses a 6 axis inertial unit so heel angle is an input data.

https://madintec.com/

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On 9/25/2019 at 6:12 PM, Puntone said:

Michel Desjoyaux said : these boats are chairs with three feet

 

The design is fundamentally flawed.  History will see that it was a mistake to bolt foils onto a conventional boat.

One look at the AC75s and you can see that is true.

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I have a B&G H5000 pilot with a hercules procesor and a 6 axis compass (not sure why it is called a compass). Heel is certainly used as an input. So I would imagine all modern pilots would also have this, difficult to see how else they could control things so effectivly.

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On 9/25/2019 at 5:22 AM, Lakrass said:

The third leg to have stability is the hull and it sails better with the back end in the water rather than the front end.

The AC45/48 sailed more bow down (with rudder foils), but I imagine in this case that when doing 25 knots + and you meet a wave bow up is preferable to “Kursk mode.”

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On 9/25/2019 at 10:30 AM, LionIsland said:

That’s some crazy shit, right there. 

But, Shirley, trying to apply that mad idea without a decent counter balancing weight, say the swinging keel,  (which, I suppose, can operate a little more “normally” in non foiling conditions) to an ocean going vessel is nigh on impossible.

 

Don’t call me Shirley.

50539863-3799-41B4-9744-0C1620C3B49B.jpeg

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1 hour ago, Jason AUS said:

The AC45/48 sailed more bow down (with rudder foils), but I imagine in this case that when doing 25 knots + and you meet a wave bow up is preferable to “Kursk mode.”

I was referring to the IMOCA rule preventing foils on rudder. Then you have keel and foil providing lift and you have to chose a third point to have some kind of stability, choice is either in front of the two legs or behind. I have never seen any boat without foil on rudder sailing bow down, which I guess would go submarine quite a lot. Only logical solution left is to go bow up to have as much stability as possible while lifting as much of the boat out of the water to reduce drag.

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All the AC boats are flat water and wind range limited..... No limits offshore, especially in the southern ocean.

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17 hours ago, dachopper said:

Depends which boat you talk about I guess.   HB has a curved foil, and I very much doubt that it has lift vectors like that on the HB foil. They go vertically up - not sideways.

Agree. HB’s arched foils are less about leeway resistance and more about lift and moving the centre of lift /dynamic buoyancy further leeward, to increase righting moment. Not much left of the keel foil in the water either...

6C20943D-6CC5-48D9-B5FA-85B0AACE26D8.jpeg

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58 minutes ago, Sidecar said:

Agree. HB’s arched foils are less about leeway resistance and more about lift and moving the centre of lift /dynamic buoyancy further leeward, to increase righting moment. Not much left of the keel foil in the water either...

6C20943D-6CC5-48D9-B5FA-85B0AACE26D8.jpeg

she's completely out of the water there.

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Yes, so the centre of dynamic buoyancy is well to leeward of the boat, unlike the “old” VPLP diagram upthread.....

it would also be interesting to know if the lift foils are really heavy, ie solid metal as opposed to solid carbon.... more reliability?

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The other thing is, because T rudder foils not allowed, HB’s rudders are more vertical and inboard than “normal”. Maybe has been a subtle tweak of geometry so that at the angles of foiling heel, the leeward rudder is also sufficiently canted to provide some lift, which means it can operate to a greater degree as a tail plane?

DF5F35EE-453C-4200-8E17-9186A0530B50.jpeg

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5 hours ago, Sidecar said:

The other thing is, because T rudder foils not allowed, HB’s rudders are more vertical and inboard than “normal”. Maybe has been a subtle tweak of geometry so that at the angles of foiling heel, the leeward rudder is also sufficiently canted to provide some lift, which means it can operate to a greater degree as a tail plane?

 DF5F35EE-453C-4200-8E17-9186A0530B50.jpeg

Maybe your onto something :)..... If the keel horizontal axis cants, there is another control....

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On 9/25/2019 at 7:34 AM, Doug Lord said:

From a friend:

IMOCA Lift.jpg

Hey Doug Lord.  Too bad none of that foiling hype you always droned on about never came true.    #deliciousirony

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Yeah, too bad............

Gitana by Stichelbaut,

Fire Arrow by Dan Burke:

Gitana_foiling_Stichelbaut.jpg

MPX_Fire Arrow-3D SAILING-7-24-14 009 (4) - Copy - Copy.JPG

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On 9/27/2019 at 6:50 AM, dachopper said:

Maybe your onto something :)..... If the keel horizontal axis cants, there is another control....

An if the (once pink, now black) lever arms of the rudders became hydraulic cylinders there is another fine tuning control....

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On 9/25/2019 at 11:35 PM, Sidecar said:

Yes I can also see that the keel foil lift is self regulating in that it’s overall heeling lift reduces with increased heel because of foil area loss whilst static righting moment increases, until you reach the point where there is insufficient total upward lift and you have splashdown?

There is obviously an optimum heel range for max foil lift, and the name of the game is to get the boat to that heel ASAP and keep it there ALAP.... Which is why they tend to sail pretty erratic courses, because it is easier and faster to head up or bear away rather that to sail trim.

I wonder if they have a algorithm in their autopilots which also responds to heel?

I would not think too much about heel. It is about incidence of the foil .. Even if you heel less or more, it still rises.. It doesn't create leeward effect because anti drift that comes from the tip of the foil . 

The point is that you sail quickly much as possible whatever condition or degree of heel. For example, Charal can foil whenever she likes and changes trajectory without losing speed. I think the hardest part is to keep the boat stable longitudinally. Thats why sail trim comes into play.

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On 9/24/2019 at 10:38 PM, Foolish said:

This is an interesting development. The original DSS (Dynamic Stability System) foils were designed to lift the stern of the boat up. And as it lifted, the foil leveled out so the stern would not keep lifting further. Rather it would settle into a position.  That's why it was called Dynamic, because the lift changed as the boat was lifted.

So I too have been looking at the new foils and how they perform. 

They are call “dynamic stability “ because the foil provides dynamic stability. The pitch stability is a handy byproduct. I find it interesting that all were saying that DSS wasn’t as good as Dali and now all of this the IMOCA are effectively using near horizontal foils more similar to DSS than Dali.

 The AC45s, AC72s and ACC (AC50) were bow down as they had sufficient control to orientate the platform so that it was the best aero position, hydro angle being far less important.

AC75 concept  will never replace a normal keelboat for anything but the AC as AVS and basic stability rules won’t let a “dinghy” go offshore. 

For the IMOCA, currently the only pitch control option is to drag the ass. More vertical rudders help, but don’t replace. A curved rudder where the tip is curved towards the centre line of the yacht with an asymmetric section might be an interesting approach, but I haven’t checked if possible in the rules. 

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1 hour ago, Chimp too said:

They are call “dynamic stability “ because the foil provides dynamic stability. The pitch stability is a handy byproduct.

I find it interesting that all were saying that DSS wasn’t as good as Dali and now all of this the IMOCA are effectively using near horizontal foils more similar to DSS than Dali.

What exactly is the definition of "dynamic stability" if it is something different from pitch stability? 

Yes, I mentioned exactly this back in August in another IMOCA thread: " I find the new and different foil shapes very interesting.  They are looking more and more like the DSS, with a long horizontal portion, and less like the dali mustache from the last generation and certainly not at all like the fumanchu of the Figaro 3."

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16 minutes ago, Foolish said:

What exactly is the definition of "dynamic stability" if it is something different from pitch stability? 

Stability as in righting moment. It is intended to lift the leeward side rather than pull down the windward side in the more traditional approach with monohull.

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So after all the chatter, the new IMCOAs are semi-foilers.   Reduces wetted surfaces, but still using the stern like a hydroplane step.

- Stumbling

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2 hours ago, Foolish said:

What exactly is the definition of "dynamic stability" if it is something different from pitch stability? 

 

it leads me to think about flexibility/complexity of carbon layout. Foils twist already while in use. Like wings of plane. It flexes and creates stability through turbulence. 

For instance, (thin) Dali foils make boat pitch up much slower but at the same time it is more stable in more varied conditions . The thick ones (Charal) make the boat pitch up faster (more acceleration but also more likely brake too)

It is like driving a car with with much power (and good "brakes") and doing badly in corners versus a car that does everything well especially in corner but without dramatic increase of acceleration and brake.

 

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4 hours ago, Chimp too said:

.....For the IMOCA, currently the only pitch control option is to drag the ass. More vertical rudders help, but don’t replace. A curved rudder where the tip is curved towards the centre line of the yacht with an asymmetric section might be an interesting approach, but I haven’t checked if possible in the rules. 

.....And/or just cant the rudders inboard more, so the leeward one becoming more horizontal is used as the elevator rudder and the windward one becoming more vertical could assist as the steering rudder?

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57 minutes ago, Sidecar said:

.....And/or just cant the rudders inboard more, so the leeward one becoming more horizontal is used as the elevator rudder and the windward one becoming more vertical could assist as the steering rudder?

too complicated with autopilot & steering hence possible drag

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...Then just use the leeward one as before. If curved rudders are allowed, I am surprised that no one has done them already, and it probably is the case that HB design team have already crunched the numbers on rudder cant and arrived at (near) vertical as being optimum.

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L shaped "curved" rudder might work. If it is allowed, what is the point to forbid T rudder?

T rudder is far better in terms of least drag and it allows more precise steering in order to change yaw angle. 

For instance, circular and non vertical rudder creates effect of pitch which forces the boat against foils. Say, rudder make the boat to pitch up but at the same time foils want to pitch down which creates drag of the opposite force of rudders and foils. It happens when you want steer which is not exactly yaw angle changing. Diffuse response is only creating headache for the skipper and autopilot. 

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10 hours ago, Sidecar said:

...Then just use the leeward one as before. If curved rudders are allowed, I am surprised that no one has done them already, and it probably is the case that HB design team have already crunched the numbers on rudder cant and arrived at (near) vertical as being optimum. 

 

8 minutes ago, troll99 said:

L shaped "curved" rudder might work. If it is allowed, what is the point to forbid T rudder?

T rudder is far better in terms of least drag and it allows more precise steering in order to change yaw angle. 

For instance, circular and non vertical rudder creates effect of pitch which forces the boat against foils. Say, rudder make the boat to pitch up but at the same time foils want to pitch down which creates drag of the opposite force of rudders and foils. It happens when you want steer which is not exactly yaw angle changing. 

Curved rudder are not allowed: rule "E.5 (f) : All points along the leading edges of the rudder shall be in the same plane."

https://www.imoca.org/en/imoca/official-documents-1

Besides that rule, making such rudders work with an autopilot would be a nightmare because of the interaction between yaw and pitch.

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12 hours ago, Sidecar said:

.....And/or just cant the rudders inboard more, so the leeward one becoming more horizontal is used as the elevator rudder and the windward one becoming more vertical could assist as the steering rudder?

That's also forbidden by class rule: "C.2 Servo Power and manoeuvring (b) Servo-control is strictly prohibited with the following exceptions: [...] (ii) the rudders to affect yaw"

I think that rule doesn't allow you to control both rudders independently.

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That rule is just to prevent you using hydraulics/power to adjust anything other than the keel cant and a traditional rudder autopilot. Theres nothing in the rule that I've seen that disallows independent control (indeed I bet its necessary when you've got a flipped up rudder) and theres nothing that prevents changing the rudder toe angle or other axis controls, it just can't be via a servo. Now how you'd manually adjust the rudder angle without a servo I haven't a clue...

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2 hours ago, Ahstom said:

That's also forbidden by class rule: "C.2 Servo Power and manoeuvring (b) Servo-control is strictly prohibited with the following exceptions: [...] (ii) the rudders to affect yaw"

In what perspective yaw? Horizontally or in yacht perspective? Even if both rudders were vertical in yacht perspective they are affecting both yaw and pitch when heeled.

Edit: And I think if rudders are canted inside (like V shape) you don't need to control both with autopilot. Only the windward one that is more vertical to control the yaw. Leeward rudder can be fixed instead of puled out and it is still stabilizing the boat and lifting the stern depending of the fixed angle. The vertical windward rudder is balancing out what ever yawing forces the leeward one is generating...

I am curious, can rudders be placed outside of hull dimensions by rules? 

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The windward rudder is generally lifted to reduce wetted surface and drag. Thinking about it, a curved rudder would simply act as a break when turned and the loads would be massive. And like elevators, not allowed anyway. 

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19 hours ago, JonRowe said:

That rule is just to prevent you using hydraulics/power to adjust anything other than the keel cant and a traditional rudder autopilot. Theres nothing in the rule that I've seen that disallows independent control (indeed I bet its necessary when you've got a flipped up rudder) and theres nothing that prevents changing the rudder toe angle or other axis controls, it just can't be via a servo. Now how you'd manually adjust the rudder angle without a servo I haven't a clue... 

I think in most cases, both rudder remain connected even when flipped up. For toe and other axis you're right, I just think that IMOCA made sure that creating lift with rudder is practically impossible with the idea to keep "old" boats competitive.

19 hours ago, pilot said:

In what perspective yaw? Horizontally or in yacht perspective? Even if both rudders were vertical in yacht perspective they are affecting both yaw and pitch when heeled. 

Edit: And I think if rudders are canted inside (like V shape) you don't need to control both with autopilot. Only the windward one that is more vertical to control the yaw. Leeward rudder can be fixed instead of puled out and it is still stabilizing the boat and lifting the stern depending of the fixed angle. The vertical windward rudder is balancing out what ever yawing forces the leeward one is generating...

I am curious, can rudders be placed outside of hull dimensions by rules? 

The class defines yaw by the movement of the yacht about the vertical axis that passes through its center of gravity

Concerning inside canted rudder: I think with  usual rudder length, usual heel angle and usual beam, the windward rudder would bearly be in the water resulting in poor yaw control. There is an issue of "the more you heel, the less steering control you have..."

The windward rudder wouldn't be very deep in the water aswell... Its efficiency would be disturbed by the messy flow of the wake.

No: "When in the "fully lowered" position the entire rudder shall fall within the limits of the hull length."

To conclude, class rules define Rudder by: "A moveable appendage primarily used to affect yaw that shall not provide vertical lift".

lifting rudder.jpg

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I understand that there is a limit longitudinally by the rules, but i meant further out from the center line. The beam is nowhere close to the limit in case of new foilers. I see that rudders can be easily developed into something else like daggerboards were developed into foils. The vertical position of the rudder is not guaranteed anyway and they acting a bit like a stabilizer. The force it crates has a yaw component and a vertical component, like with T rudders. The attack-angle of the hull dictates how much average lift is generated. The pulling force of sails generates a yaw moment that forces the autopilot to turn downwind and this also makes the rudder to generate more lift. The angle of attack will depend a lot of the needed yaw moment but this can be corrected by changing foils angle of attack. It would be much easier to sustain flying if the rudder fin would be placed outside of hull and pointing more inside. The closer to the center line the more of it comes out of water during liftoff by the help of heeling. 

 

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On Advens for Cybersecurity (T. Ruyant), they are very happy to have reach their goal wich was 1 to 1.5 meters high (they dont't say where, but I guess at the bow), where others fly at 3 to 4.5 meters high !

They chose to make less profound foils than the others for that

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