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On 4/29/2021 at 1:41 PM, MaxHugen said:

On either side of the wing base on the forward cross beam, there's something that looks like a big louvre. Anyone have a guess as to what they might be?

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Non Skid tape .

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  • 2 weeks later...

Looks like the crossbeams both have some camber to them... the forward beam providing a bit of lift, the aft beam some down force.

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On 5/13/2021 at 12:35 AM, MaxHugen said:

Looks like the crossbeams both have some camber to them... the forward beam providing a bit of lift, the aft beam some down force.

Or they're just trying to minimise drag…

Given there's no class rule to limit anything, i.e. SailGP can design the boats to do whatever it wants, why build in a bias to the platform?

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29 minutes ago, RobG said:

Or they're just trying to minimise drag

Given there's no class rule to limit anything, i.e. SailGP can design the boats to do whatever it wants, why build in a bias to the platform?

Could be, I don't know. 

I have observed the F50 sailing very level for a period, didn't take a note of the speed though I should have.

I think that at higher speeds they are flying pitch down, to reduce rudder drag. This angle might also reduce drag from the beams.

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  • 2 months later...

This is somewhat off topic, but for anyone interested in design, Niall has a great interview with yacht designer Juan Kouyoumdjian about the development of foils (and hulls) for the IMOCAs.   Fascinating!

 

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28 minutes ago, Stingray~ said:

There’s another site, French, that may have simple CAD designs you could blow up to whatever size you like, Chevalier or something? 

edit, these guys http://chevaliertaglang.blogspot.com/2019/08/americas-cup-2021-ac-75-drawings_13.html?m=1

He has AC72s and AC75s drawn up, but no AC50s for a SailGP model. I know a few people in this thread made CAD models of F50s, so wanted to ask here.

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^ my point is not that we will see this in AC37, but that the AC drives sailing evolution with novel solutions to existing challenges. The AC75 class copped a lot of flak at the start, but performed immaculately in the finals.

Anyone suggesting to do AC37 in a dumbed down version of the last boat misses the point.

A more in depth proof of the craft above

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41 minutes ago, barfy said:

^ my point is not that we will see this in AC37, but that the AC drives sailing evolution with novel solutions to existing challenges. The AC75 class copped a lot of flak at the start, but performed immaculately in the finals.

Anyone suggesting to do AC37 in a dumbed down version of the last boat misses the point.

A more in depth proof of the craft above

I researched this a long time ago, quite fascinating.  

The inventor, Rick Cavallaro, had a cool explanation - which I haven't found again. :(

Very basically, he used the example of a sail boat gybing downwind, with VMG faster than wind speed. He then illustrated this in a diagram, not as a boat travelling across a flat water surface, but around a round tube.  Now, the sail "became" one blade of a "propeller".

@barfy if you search back through Rick's early publications (I don't recall if it was a video, probably just a blog post), you'll probably find this awesome illustration...  as soon as I saw it, the theory "clicked" for me.  :rolleyes:

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4 hours ago, MaxHugen said:

I researched this a long time ago, quite fascinating.  

The inventor, Rick Cavallaro, had a cool explanation - which I haven't found again. :(

Very basically, he used the example of a sail boat gybing downwind, with VMG faster than wind speed. He then illustrated this in a diagram, not as a boat travelling across a flat water surface, but around a round tube.  Now, the sail "became" one blade of a "propeller".

@barfy if you search back through Rick's early publications (I don't recall if it was a video, probably just a blog post), you'll probably find this awesome illustration...  as soon as I saw it, the theory "clicked" for me.  :rolleyes:

It's in the first video...brilliant diagram. 

Did any boats get a solid 2.8 x windspeed towards mark over an entire leg?

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2 hours ago, barfy said:

It's in the first video...brilliant diagram. 

Did any boats get a solid 2.8 x windspeed towards mark over an entire leg?

Ah right, it's from about 7:00 onward.

I don't think anyone is gathering data on the F50 races, so I'm unsure if they've done 2.8x for an entire downwind leg, but I strongly suspect it's been beaten by a decent margin.

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Where is the center of lift on any of these wings?  Is it stable (like how much does it move around?)?  What kind of drag is involved with any changes relative to the center of lateral resistance of the platform?  Is the center of lateral resistance of these platforms stable, either hydro or aero?

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9 hours ago, Amati said:

Where is the center of lift on any of these wings?  Is it stable (like how much does it move around?)?  What kind of drag is involved with any changes relative to the center of lateral resistance of the platform?  Is the center of lateral resistance of these platforms stable, either hydro or aero?

The CE for these wingsails varies - a lot. Much depends on the amount of twist, which I believe can be as much as 40°.

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1 hour ago, MaxHugen said:

The CE for these wingsails varies - a lot. Much depends on the amount of twist, which I believe can be as much as 40°.

Might explain why they need wheels.  
 

And the point of lateral resistance?

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45 minutes ago, Amati said:

Might explain why they need wheels.  
 

And the point of lateral resistance?

I'm not quite sure what you mean by "point of lateral resistance"?  If that is resistance to leeway, it's mainly a function of the foil.

Being roughly "L" shaped, the vertical component of the foil provides most of the lift to windward, thus reducing leeway.

To a minor degree, the rudders also provide windward lift, and the wingsail may too, if twist is increased to the point where the upper section of the wing is in a position of "inverse camber".

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1 hour ago, MaxHugen said:

I'm not quite sure what you mean by "point of lateral resistance"?  If that is resistance to leeway, it's mainly a function of the foil.

Being roughly "L" shaped, the vertical component of the foil provides most of the lift to windward, thus reducing leeway.

To a minor degree, the rudders also provide windward lift, and the wingsail may too, if twist is increased to the point where the upper section of the wing is in a position of "inverse camber".

My bad- wasn’t clear- does the point (as in the sum) of longitudinal resistance move around between the keels (what are they called- leeboards? Daggerboards?) and the rudders?  At any rate, between foils, or even on individual foils?  For example, if the center of lift of the wing moved 40% towards the stern, would flow hysteresis on the rudder system hold long enough prevent any tendency to spin out?  Would there be weather helm as a result that would need to be corrected by the helm, stressing the flow on both foils?  Or can main trim catch things before they happen?   Watching the last AC, it seemed to me that the helm on most of the boats was a busy place as far as steering went.

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26 minutes ago, Amati said:

My bad- wasn’t clear- does the point (as in the sum) of longitudinal resistance move around between the keels (what are they called- leeboards? Daggerboards?) and the rudders?  At any rate, between foils, or even on individual foils?  For example, if the center of lift of the wing moved 40% towards the stern, would flow hysteresis on the rudder system hold long enough prevent any tendency to spin out?  Would there be weather helm as a result that would need to be corrected by the helm, stressing the flow on both foils?  Or can main trim catch things before they happen?   Watching the last AC, it seemed to me that the helm on most of the boats was a busy place as far as steering went.

These are complex questions!  To the best of my limited ability:

  1. Foils.  Due to their shape, they provide both vertical lift, and lateral lift (like a keel).  To minimise drag, the teams try to fly the F50s as high as they can without causing the foil to ventilate, thus stalling the foil.  Ride height is largely governed by raking the foil.
    In addition, the higher they fly, the less lateral lift the foil generates, which increases the leeway. Note that in most cases, only the leeward foil is down except when executing a tack or gybe.
  2. Wings.  Changes in twist alters the height of the CE (ie, in the Z plane). Adding twist decreases power in the upper sections, thus lowering the CE, which improves the Righting Moments.
    Changes to the camber will tend to alter the position of the CE in the X plane, but not to anything like 40%, probably a couple of percent at most. However, the rudders still need to compensate for this.
  3. Rudders.  The teams also try to keep these as high as possible to minimise drag, without losing rudder control or ventilating the rudder foils.  Raking the rudder changes the AoA of the rudder foils. 
    However, there is a differential between the rake of the leeward rudder vs that of the windward rudder.  The windward rudder uses a "negative" rake to create a downward force of up to around one tonne, thus contributing to Righting Moment.

Coordinating the combined forces from these is indeed a fine art!

The AC75 has a unique issue that is not experienced by the F50.  Whilst the F50 generally uses 3 points of ± Lift (one foil, two rudders), the AC75 generally uses 2 (one foil, one rudder), and these are offset from the X plane centreline. This asymmetric geometry results in the AoA of the main foil to increase when the boat suddenly heels due to a gust, which can often result in a "sky jump". They are very touchy to control!

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27 minutes ago, Mozzy Sails said:

Holy testicles 

May be an image of body of water

Trying to figure out just what they were doing at that moment!  Astonishing bend on the rudder... maybe in a high speed tack or gybe?

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