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I didn’t write (or necessarily support) the IMOCA rule, some highly experienced Frenchmen did, and who history has shown aren’t scared of innovation.

IMOCA boats are designed to be crewed solo/short handed 24/7 through any kind of weather and sea state that mother nature cares to throw at them and be totally self sufficient , whilst AC75’s are craft that sail in protected flat waters, in limited wind ranges with a flotilla of support craft nearby by a crew of 11 for short periods of time who get a good  sleep every night. They can also call lay days to repair damage.

But you are right, these are interesting times in terms of yacht design and it will be interesting to see what cross over of techniques and ideas happen between the different codes of yacht racing.

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https://www.sailingworld.com/story/racing/sails-of-the-americas-cup/ The Sails of the America’s Cup Between the skins of the AC75 mainsail lies the secrets to powering the latest generation

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7 hours ago, Sidecar said:

I didn’t write (or necessarily support) the IMOCA rule, some highly experienced Frenchmen did, and who history has shown aren’t scared of innovation.

IMOCA boats are designed to be crewed solo/short handed 24/7 through any kind of weather and sea state that mother nature cares to throw at them and be totally self sufficient , whilst AC75’s are craft that sail in protected flat waters, in limited wind ranges with a flotilla of support craft nearby by a crew of 11 for short periods of time who get a good  sleep every night. They can also call lay days to repair damage.

But you are right, these are interesting times in terms of yacht design and it will be interesting to see what cross over of techniques and ideas happen between the different codes of yacht racing.

It's a pity that the French don't mount an AC challenge. Their designers et al have a wealth of experience with foiling.

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45 minutes ago, MaxHugen said:

It's a pity that the French don't mount an AC challenge. Their designers et al have a wealth of experience with foiling.

They did that last time remember?

The only thing they achieved was to confirm the reality that talent alone cannot win the AC. For that, you need time, talent, luck and a shit tonne of money.

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1 hour ago, jaysper said:

They did that last time remember?

The only thing they achieved was to confirm the reality that talent alone cannot win the AC. For that, you need time, talent, luck and a shit tonne of money.

Hmmm, yes. They were so impressive I completely forgot about them! :unsure:

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@erdb how are you calculating hull drag and side force in your equations?

Longitudinal: Drive x CoE_z - Weight x CG_x + Stab lift x CoE_x(stab) - Hull_drag x CoE_z(hull) = 0
Transverse: Heel x CoE_z - Weight x CG_y + Stab lift x CoE_y(stab) +  Hull_sideforce x CoE_z(hull) = 0

I calc hull drag with Cd=0.30 and Hull Area (frontal) with 9.0m2, for a CdA of 2.7 - similar to what you use I think. But no allowance for AoA?

PS:  shouldn't sail drag be added to longitudinal moments as well as hull drag? And induced drag for both...

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53 minutes ago, MaxHugen said:

@erdb how are you calculating hull drag and side force in your equations?

Longitudinal: Drive x CoE_z - Weight x CG_x + Stab lift x CoE_x(stab) - Hull_drag x CoE_z(hull) = 0
Transverse: Heel x CoE_z - Weight x CG_y + Stab lift x CoE_y(stab) +  Hull_sideforce x CoE_z(hull) = 0

I calc hull drag with Cd=0.30 and Hull Area (frontal) with 9.0m2, for a CdA of 2.7 - similar to what you use I think. But no allowance for AoA?

PS:  shouldn't sail drag be added to longitudinal moments as well as hull drag? And induced drag for both...

Yes, pretty much the same for hull drag. Obviously far from ideal, but I think it doesn't have a huge effect overall. I used cd=0.4 and frontal area 6 m2. I'm sure your area measurement is more accurate, but we should be getting pretty similar drag values. There is obviously quite a bit of lift (sideways) generated by the hull, but it would be complicated to predict how AWA affects that. I just calculate drag, and the resultant drag force is in line with the AWA, so it does have a longitudinal and a transverse component.

Sail forces (lift and drag) are also converted to longitudinal (drive) and transverse (heel) components. The longitudinal goes into the pitch balance, the transverse into the roll balance.

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Just thought I'd link it here, too from the INEOS thread. The lower left and right pics are the best I've seen so far indicating negative AoA at the top of the main. Actually they only seem to bend out the aft end of the top. This way the flow is smooth at the mast, which needs to be rotated to match the rest of the sail. It's kind of an S curve.

http://forums.sailinganarchy.com/index.php?/topic/211990-ineos-team-gb/&do=findComment&comment=7321893

 

2066490102_INEOS1twist.thumb.jpg.ca4e26c74d04b9811ab7d6e1b465144c.jpg

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On 12/16/2020 at 4:44 PM, Kiwing said:

For me it is the leeside of the wing during climbing onto the foils which is the difference.
Reversing the top for stability Ineos seem to be struggling with too

I'm not yet convinced that anyone is reversing the top of the main.  With the mast rotated one way, and the sail being forced the other way for RM, I can't see as this as adding leeward lift, but definitely increasing drag.

Maybe down the track we'll be able to grab some top-down pics when they are actually racing...

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These Port And Starboard Entry camera feeds are showing some great views on the sail trim and config differences between boats. AM seems to be adjusting the windward/leeward mainsail clews the most of all boats. I reckon a good 4-6inches looser outhaul on leeward sail on each tack. Ineos also appears to have way more mainsail depth up forward compared to any of the others... LR is very neat. 
check it out 

Port entry https://youtu.be/XevjFVrYMvw

Stb entry https://youtu.be/Hn8p1eGmjn0

 

 

 

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I suspect the rotating mast is a big part of the value of the set up in the AC75 main sail system and it seems to get little press aside from occasional acknowledgment that it is a part of the rule.  Does anyone know how the masts are rotating with the fixed rigging to the side stays?  I think a similar set up was done at one point in the Open 60s when some boats did not use deck spreaders.  

The mast rotation is not substantial from what I have seen. I would guess it is in the range of 45 degrees in total range but have no idea what the limits are.

I agree, Saro Scimitar, very interesting to see LR has no backstays and is relying on the side stays and mainsheet tension.  Perhaps they also carry higher Cunningham tension as needed for mast bend.

 

 

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2 minutes ago, Lost in Translation said:

Does anyone know how the masts are rotating with the fixed rigging to the side stays?

They rotate on a ball joint on the bottom, and the spreaders aren't fixed.

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Rotating rigs I've used have had diamond spreaders and stays so that the rig is supported side to side regardless of rotation angle and then other stays supporting the mast's position overall.  The AC75s present a more traditional looking rigging package with the stays going to fixed chainplates.  How does it work?

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7 minutes ago, Lost in Translation said:

Rotating rigs I've used have had diamond spreaders and stays so that the rig is supported side to side regardless of rotation angle and then other stays supporting the mast's position overall.  The AC75s present a more traditional looking rigging package with the stays going to fixed chainplates.  How does it work?

Spreaders are gimballed at the mast, I believe.

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4 hours ago, Saro Scimitar Sunshine said:

No running backstays on Luna Rossa last night. Seems to work, so there's some aero drag and weight saving. Will the others follow ?

Capture d’écran 2020-12-18 à 10.59.39.png

I was rather surprised by this! The mast bend that other teams are getting does a lot to flatten the mainsail in the upper sections, where it's needed, yet allow the lower sections to keep some deeper camber.  Don't think the cunningham &/or more leech tension can really do that?

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Definitely a concern.  Add headstay tension to the list of concerns as well.

is LR running more swept back spreaders to try to compensate?

The main sheet tensions must be enormous on these boats and maybe LR made an argument that the backstay would carry very little load with such high mainsheet tension.

 

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1 hour ago, ed__miller said:

These Port And Starboard Entry camera feeds are showing some great views on the sail trim and config differences between boats. AM seems to be adjusting the windward/leeward mainsail clews the most of all boats. I reckon a good 4-6inches looser outhaul on leeward sail on each tack. Ineos also appears to have way more mainsail depth up forward compared to any of the others... LR is very neat. 
check it out 

Port entry https://youtu.be/XevjFVrYMvw

Stb entry https://youtu.be/Hn8p1eGmjn0

 

 

 

Ineos has a kink in their boom not too far from the mast.  You can see it bending in some of the video shots.  That allows them to "force" the shape of the sail.

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Yes you can see the sheets each side too pulling it through the tacks/gybes. Looks to be controlled by Mon’s keypad. Still not convinced he is manually playing the traveller. It seems to move even though he is not holding the keypad. He is definitely not playing the outhaul anything like AM. Do you reckon that Ineos are playing sail shape from the headboard instead?

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34 minutes ago, MaxHugen said:

I was rather surprised by this! The mast bend that other teams are getting does a lot to flatten the mainsail in the upper sections, where it's needed, yet allow the lower sections to keep some deeper camber.  Don't think the cunningham &/or more leech tension can really do that?

 

5 hours ago, Saro Scimitar Sunshine said:

No running backstays on Luna Rossa last night. Seems to work, so there's some aero drag and weight saving. Will the others follow ?

Capture d’écran 2020-12-18 à 10.59.39.png

Capture d’écran 2020-12-18 à 11.00.22.png

Capture d’écran 2020-12-18 à 11.07.24.png

On the YouTube broadcast, they talked about this in one of the AM vs LR races on the second day.  AM seemed to have much more bend in the mast (like NZ did) and they showed what they thought was a kink in the LR mast caused by not having the backstay.  I didn't really see it, but they know much more about it than I will even pretend to know.

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11 hours ago, Saro Scimitar Sunshine said:

No running backstays on Luna Rossa last night. Seems to work, so there's some aero drag and weight saving. Will the others follow ?

Two less things to worry about when you are manoeuvring as well? And they are doing smooth turns?

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7 hours ago, Lost in Translation said:

Rotating rigs I've used have had diamond spreaders and stays so that the rig is supported side to side regardless of rotation angle and then other stays supporting the mast's position overall.  The AC75s present a more traditional looking rigging package with the stays going to fixed chainplates.  How does it work?

Same as a A?

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6 hours ago, ed__miller said:

Ken Reed pointed out the “kink” as being in the forestay just at the top of the jib. There was an obvious deflection as it had little load in it due to no runners 

Unavoidable if you have a (small square headed) jib and some full length battens in it. It is the leach tension acting perpendicularly through the square head.  You can’t get enough luff tension to overcome the catenary forces.

Don’t ask me how I know......

B4B02435-20FE-4AEC-A165-EE8FDCB8A697.jpeg

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11 hours ago, Saro Scimitar Sunshine said:

No running backstays on Luna Rossa last night. Seems to work, so there's some aero drag and weight saving. Will the others follow ?

Capture d’écran 2020-12-18 à 10.59.39.png

Capture d’écran 2020-12-18 à 11.00.22.png

Capture d’écran 2020-12-18 à 11.07.24.png

Maybe it's their way of sandbagging?

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On 12/12/2020 at 2:09 AM, erdb said:

That's when I incorporated wave and spray drags and after that, it all came together. So even though I'm not fully confident about how I calculate these foil drags, it must be more or less accurate, because this is what works with the "anatomy" of the boat that we know quite accurately.

How did you calculate wave/spray drag? Haven't been able to find anything on it.

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3 hours ago, MaxHugen said:

How did you calculate wave/spray drag? Haven't been able to find anything on it.

For spray drag, I found this paper: https://foils.org/spray-drag-of-surface-piercing-struts/

and used that very simple formula on the first page, D_spray = 0.24 x qt^2 (see the list of abbreviations in the paper)

For wave making, I forgot, but somewhere I found a paper with some graphs on how running a foil at various depth changes waves and drag and there was a graph showing some cd values, and from that I took one that looked OK (cd_wave = 0.011). I just add this to cd_visc to make the drag higher. This is obviously not correct, I'm sure the waves and the drag associated with them also depend on the lift the foil is generating, but it just seems a way too complex problem for me to solve. However, it was kind of interesting to see how as I was increasing foil drag, suddenly everything started to come together and balance out in the model. Basically it's reverse engineering from the dimensions of the boat. There is a reason the class rules are set the way they are, so even if my drag calculations are not perfect, they must be in the ballpark, otherwise I couldn't balance the boat with its well-known dimensions and weight. Plus, the boat speeds we saw so far match the model's predictions very nicely.

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7 hours ago, erdb said:

For spray drag, I found this paper: https://foils.org/spray-drag-of-surface-piercing-struts/

and used that very simple formula on the first page, D_spray = 0.24 x qt^2 (see the list of abbreviations in the paper)

For wave making, I forgot, but somewhere I found a paper with some graphs on how running a foil at various depth changes waves and drag and there was a graph showing some cd values, and from that I took one that looked OK (cd_wave = 0.011). I just add this to cd_visc to make the drag higher. This is obviously not correct, I'm sure the waves and the drag associated with them also depend on the lift the foil is generating, but it just seems a way too complex problem for me to solve. However, it was kind of interesting to see how as I was increasing foil drag, suddenly everything started to come together and balance out in the model. Basically it's reverse engineering from the dimensions of the boat. There is a reason the class rules are set the way they are, so even if my drag calculations are not perfect, they must be in the ballpark, otherwise I couldn't balance the boat with its well-known dimensions and weight. Plus, the boat speeds we saw so far match the model's predictions very nicely.

Thanks, got the equation. I'll see how my drag is adding up!

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ETNZ have far more camber in the bottom couple of metres of main sail to accelerate them from slow to foiling.  Then they flatten it off very quickly.  Being down very low the COE requires little RM?

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3 hours ago, Kiwing said:

ETNZ have far more camber in the bottom couple of metres of main sail to accelerate them from slow to foiling.  Then they flatten it off very quickly.  Being down very low the COE requires little RM?

Sort of.  Lowering the CE reduces the Heeling Moment, so it can be balanced against the available RM.

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1 hour ago, barfy said:

I see the etnz main sail(s) gap was strong during the regatta. Long live the gap!!

Ah, the gap!   I have noticed that at other times, their main is "gapless" apart from the first couple of metres from the clew.

Perhaps this is to create an increase in effective sail area by using the Kammback effect?  Would seem to fit the scenario: light winds, open the gap all the way up for more sail area. Then reduce the gap, except low down on the sail, as wind picks up and they start increasing twist.

Or not. :unsure:

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6 hours ago, Kiwing said:

ETNZ have far more camber in the bottom couple of metres of main sail to accelerate them from slow to foiling.  Then they flatten it off very quickly.  Being down very low the COE requires little RM?

The boomless setup has a lot of challenges, but I think this is the magic.  Where Amway have to slide the skins to generate that pressure differential to gain power for takeoff, ETNZ can just tension the clew puller and generate a totally crazy depth and shape to power the bottom of the sail.  Really impressed. 

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53 minutes ago, Xlot said:

But TR still has an articulated boom carried over from TA, right?

 

Don't belivee TR has anything you'd call a boom. I think there is the mainsheet, another ram pushing battens, possibly ANOTHER ram doing who-knows-what, plus the lacing that tensions the foot gap, plus a guy that pulls the clew fwd for shaping against the battens. A lot going on there, but not sure there's any rigid member you could call a boom. 

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38 minutes ago, RMac said:

Don't belivee TR has anything you'd call a boom. I think there is the mainsheet, another ram pushing battens, possibly ANOTHER ram doing who-knows-what, plus the lacing that tensions the foot gap, plus a guy that pulls the clew fwd for shaping against the battens. A lot going on there, but not sure there's any rigid member you could call a boom. 

Yeah, I think you're right -

  • main ram = mainsheet
  • 2 smaller rams = one for each clew for both outhaul and to adjust foot tension separately
  • 1 ram (not visible) that adjusts a lever that the clew rams swivel on, to adjust leech tension
  • 2 rams attached to mast "spanners" to bend the battens for camber
  • 1 ram for the cunningham luff tension
  • lacing to tension the deck-sweeping skirt

BUT... I think they are also adjusting... the GAP!  Haven't figured out how they would do that, if indeed that is the case?

 

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2 hours ago, RMac said:

The boomless setup has a lot of challenges, but I think this is the magic.  Where Amway have to slide the skins to generate that pressure differential to gain power for takeoff, ETNZ can just tension the clew puller and generate a totally crazy depth and shape to power the bottom of the sail.  Really impressed. 

The camber of the leeward skin is what creates the low pressure, and thus the lift/drag forces. I think the windward skin is tensioned a bit to prevent boundary layer separation, especially in the area of greatest camber, which will cause additional drag.

But I agree that NZ's method of developing substantial camber low down is impressive!

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On 12/11/2020 at 3:42 AM, Kiwing said:

2065790213_Fatsail.thumb.jpg.1fc6ef3886b3c5292105cfd52b34330e.jpg

Food for thought?

Hey @GeeJay could I ask you to do one of your magic AI enhancements on this image pls?

There looks like some sort of strut (?) going from the clew area in between the skins, which has aroused my curiosity, but the image is too blurry to make much out when zoomed in.

Only if you're not to busy prepping for Xmas! :) 

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32 minutes ago, Kate short for Bob said:

Is it allowed under the rules and is it possible to allow air to flow between the two skins?  

I considered that they might be aiming for an airflow through the skins to help the "Kammback" gap maintain a smoother airflow via less turbulence, more laminar flow.

But I've looked at the sails etc, can't see where they'd get enough air in to provide the volume of air for a substantial gap?  Use the mast as a snorkel? :D

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1 hour ago, Kate short for Bob said:

Is it allowed under the rules and is it possible to allow air to flow between the two skins?  

Only small openings in the back of the mast.although the rule doesn't seem to preclude openings in the front of the mast it has to be to drawings, which I expect would be iges and have no holes. No where I saw rules out openings in the sails themselves.

No other team is sporting a gap, which makes it more interesting..a diversion or a feature?

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2 hours ago, erdb said:

No gaps, the sail skins have to be attached continuously to the mast.

1359449569_mainsailrule.thumb.JPG.878c96d3e163527077e78ead730091bf.JPG

I wonder if air could be sucked in from the head of the sail. Might even help reduce tip vortex there?

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7 hours ago, MaxHugen said:

Hey @GeeJay could I ask you to do one of your magic AI enhancements on this image pls?

There looks like some sort of strut (?) going from the clew area in between the skins, which has aroused my curiosity, but the image is too blurry to make much out when zoomed in.

Only if you're not to busy prepping for Xmas! :) 

Hi Max,

Have had a go but original resolution is too poor to get anything out of it.  Somewhere, there's a video (TVNZ) I think showing one of the team  disassembling it at the end of a race whilst one of the crew was being interviewed which may be on TVNZ or YouTube.  It could have been the last race that was abandoned it.  I was only half-watching at the time but my faulty memory suggested that it was a worm arrangement.  If you can find it, you'll see the detail clearly.

We have family arriving tomorrow so I'll be out of commission for a few days.  Have a great Christmas!

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18 minutes ago, GeeJay said:

Hi Max,

Have had a go but original resolution is too poor to get anything out of it.  Somewhere, there's a video (TVNZ) I think showing one of the team  disassembling it at the end of a race whilst one of the crew was being interviewed which may be on TVNZ or YouTube.  It could have been the last race that was abandoned it.  I was only half-watching at the time but my faulty memory suggested that it was a worm arrangement.  If you can find it, you'll see the detail clearly.

We have family arriving tomorrow so I'll be out of commission for a few days.  Have a great Christmas!

Max,

Just had a rapid look on the TVNZ website and couldn't find the interview I mentioned but did a screen grab and ran it through Gigapixel at twice scale - best I could do.  Looks like a hydraulic ram but not sure if it's the same component that I remember being removed.

TR2-gigapixel-scale-2_00x.jpg

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19 minutes ago, GeeJay said:

Hi Max,

Have had a go but original resolution is too poor to get anything out of it.  Somewhere, there's a video (TVNZ) I think showing one of the team  disassembling it at the end of a race whilst one of the crew was being interviewed which may be on TVNZ or YouTube.  It could have been the last race that was abandoned it.  I was only half-watching at the time but my faulty memory suggested that it was a worm arrangement.  If you can find it, you'll see the detail clearly.

We have family arriving tomorrow so I'll be out of commission for a few days.  Have a great Christmas!

Thanks for having a go!  I'll see what other pics/vids might show it clearer. A worm arrangement... had not thought of that possibility.

Best wishes to you and family.for Xmas and a healthy 2021.   Cheers, Max.

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4 minutes ago, GeeJay said:

Max,

Just had a rapid look on the TVNZ website and couldn't find the interview I mentioned but did a screen grab and ran it through Gigapixel at twice scale - best I could do.  Looks like a hydraulic ram but not sure if it's the same component that I remember being removed.

TR2-gigapixel-scale-2_00x.jpg

Thanks, clearer image, but raises yet more questions! Like, what is the T piece at the top of the main ram thingy...? It does however clearly confirm that the "camber enhancement device" is anchored to the end of the mainsheet ram, as suggested by others.

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1 hour ago, GeeJay said:

Hi Max,

Have had a go but original resolution is too poor to get anything out of it.  Somewhere, there's a video (TVNZ) I think showing one of the team  disassembling it at the end of a race whilst one of the crew was being interviewed which may be on TVNZ or YouTube.  It could have been the last race that was abandoned it.  I was only half-watching at the time but my faulty memory suggested that it was a worm arrangement.  If you can find it, you'll see the detail clearly.

We have family arriving tomorrow so I'll be out of commission for a few days.  Have a great Christmas!

The video was of one of the early races, perhaps end of day one IIRC.  It was posted somewhere here, perhaps the Christmas cup thread.

PB was being interviewed, standing near the middle of the boat while others were taking the main sheet off in the back ground.

GD would have had steam coming out his ears when he viewed the video later.

After the last race BT stood at the outside corner of the stern, with the chase boat in the back ground.  The boyz might stuff up but they rarely make the same mistake twice

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The big ram looks a relatively simple main sheet depending on what it’s attached to inside the sails that we can’t see? The batten rams look interesting and must be assisting with camber some how but I guess they must work in conjunction with mast rotation to move the chord depth for and aft? 

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1 hour ago, ed__miller said:

The big ram looks a relatively simple main sheet depending on what it’s attached to inside the sails that we can’t see? The batten rams look interesting and must be assisting with camber some how but I guess they must work in conjunction with mast rotation to move the chord depth for and aft? 

I don't think it's a ram, for mainsheet control. Maybe a linear actuator... ?

image.png.65c04f518aa1b1d7c35251f92180165d.png

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1 hour ago, ed__miller said:

The big ram looks a relatively simple main sheet depending on what it’s attached to inside the sails that we can’t see? The batten rams look interesting and must be assisting with camber some how but I guess they must work in conjunction with mast rotation to move the chord depth for and aft? 

What we are seeing is the conjunction of sailors leading the design team in terms of what they want, and the builders having to make it happen. Maybe not perfect first time round but doing what it should. Fascinating

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34 minutes ago, MaxHugen said:

I don't think it's a ram, for mainsheet control. Maybe a linear actuator... ?

image.png.65c04f518aa1b1d7c35251f92180165d.png

The small black object at the top of the ram seems to be how they keep the gap. Wonder if there are more of them running up the leech?

The big black object I think is just a bearing to allow the attachment of 2 skins to the cylinder, just allows for articulation I think.  Floating the ram on that strop allows them to move it fore/aft with those camber guys.  

Starting to wonder if some of these boats are running tubular telescoping battens that can get pushed to straighten them. I thinkI recall that pneumatic battens were verboten (verbatten! sorry, I'll go...) but mechanical adjustment OK, right?

Either way NZ have to be moderately annoyed about that nice high res sequence!

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7 hours ago, MaxHugen said:

I don't think it's a ram, for mainsheet control. Maybe a linear actuator... ?

image.png.65c04f518aa1b1d7c35251f92180165d.png

If you have the time and skill... see if you can grab a shot of the black, toothed (?) bar that is removed

It appears right at the end of the video and there are two of them.

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1 hour ago, Rushman said:

If you have the time and skill... see if you can grab a shot of the black, toothed (?) bar that is removed

It appears right at the end of the video and there are two of them.

There are two tracks that get pinned to the the other half which looks bolted to each skin once the main is hoisted, i think they operate like this old tech..... each skin has one and the main sheet cylinder can float between them.

Capture11.PNG

Capture55.PNG

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1 hour ago, XPRO said:

There are two tracks that get pinned to the the other half which looks bolted to each skin once the main is hoisted, i think they operate like this old tech..... each skin has one and the main sheet cylinder can float between them.

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Your use of the term “float” might be over simplifying it, the ram attached might enable adjustments to a fraction of a bees dick :lol:

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3 hours ago, Rushman said:

If you have the time and skill... see if you can grab a shot of the black, toothed (?) bar that is removed

It appears right at the end of the video and there are two of them.

I had taken some snaps as they dismantled that section... intriguing ! They hang off a couple of struts, but I haven't determined where/how the top of the struts are anchored. The "teeth" are the lugs that the struts match up to, different lugs depending on the foot length of the different mainsails.

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My best guess is..

The rod in the middle row of photos passes through the lugs and also through webbing loops on the sail

The small rams control the clew position, the main sheet is the common attachment point

How it works after that is way above my pay grade

 

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33 minutes ago, Kiwing said:

111ineos.thumb.jpg.0770adcc36e23c16213e4cc1ddc22056.jpg
interesting shape down low?

Odd looking profile!  The flattened area just aft of the luff could be because they need to ease the jib further out on the traveller?

And the aft third of the main looks like it has a slight reverse curve... 

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The sail program for GBR in 2002-3 had difficulty producing a main without reflex in the leech in the bottom half of the sail. They ended up using their lightest main for all windspeeds as it was the only one that would work at all

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47 minutes ago, nroose said:

Seems unlikely that it would be that thick that far away from the mast, but perhaps I am missing something.

Look at the Photo above that is where those lines come from.
And that is my point that everyone does not think this is happening but it is, just that we don't get any photos from on top.
but the interesting part is near the leech, slightly concaved, which is strange?

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49 minutes ago, Kiwing said:

Look at the Photo above that is where those lines come from.
And that is my point that everyone does not think this is happening but it is, just that we don't get any photos from on top.
but the interesting part is near the leech, slightly concaved, which is strange?

Yes, that concavity does seem strange. I guess I don't see as much thickness as you do in that shot.

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8 minutes ago, nroose said:

Yes, that concavity does seem strange. I guess I don't see as much thickness as you do in that shot.

The thin arrow is the apparent wind denoted by the top of the mast.  I assume the windward skin starts paralell to that but we can not see it. The leeward skin (which we can see) is drawn as best I can.  and so the thickness?

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19 minutes ago, Kiwing said:

The thin arrow is the apparent wind denoted by the top of the mast.  I assume the windward skin starts paralell to that but we can not see it. The leeward skin (which we can see) is drawn as best I can.  and so the thickness?

Ah. I guess I would not assume that the windward skin would be parallel to the apparent wind.

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2 hours ago, nroose said:

Ah. I guess I would not assume that the windward skin would be parallel to the apparent wind.

You want the flow to adhere so surely you want the windward skin to start where the mast finishes.  The thicker the more pressure difference and hence more lift. No separation means less drag?

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59 minutes ago, Kiwing said:

You want the flow to adhere so surely you want the windward skin to start where the mast finishes.  The thicker the more pressure difference and hence more lift. No separation means less drag?

Oh, I agree that they want thickness, at least some of the time. I am just not sure how they get that with a decent shape. And I have not really seen anything definitive that indicates thickness. Just trying to imagine how these twin skin sails work.

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