Kiwing

The new sailing twin skin setup

Recommended Posts

3 hours ago, Colomba said:

 The only important tech metric is efficiency, thus outright performance, and in that regard the wing is king, end of discussion.

Problem is they mounted the new one on a retired AC boat. Not so efficient

Share this post


Link to post
Share on other sites
6 hours ago, Kiwing said:

Do you have a wing on your personal boat?  Or crane to lift in on?

Irrelevant, try again.

3 hours ago, barfy said:

Problem is they mounted the new one on a retired AC boat. Not so efficient

Platform is also irrelevant, we’re only talking rig performance here since both rig types works on both platforms. Then again, a platform designed for a wing doesn’t need to withstand any leech, sheet or stay tension...

Share this post


Link to post
Share on other sites
1 hour ago, Colomba said:

Irrelevant, try again.

Platform is also irrelevant, we’re only talking rig performance here since both rig types works on both platforms. Then again, a platform designed for a wing doesn’t need to withstand any leech, sheet or stay tension...

You said (above) that it was the end of the discussion!

Share this post


Link to post
Share on other sites
8 hours ago, Colomba said:

 The only important tech metric is efficiency, thus outright performance, and in that regard the wing is king, end of discussion.

I posted it here because I thought it would be of interest.

 

Is everything always a competition with you?  Does that affect your personal and professional life?

Share this post


Link to post
Share on other sites
5 hours ago, Ex-yachtie said:

I posted it here because I thought it would be of interest.

 

Is everything always a competition with you?  Does that affect your personal and professional life?

Apparently affects yours.

5 hours ago, Ex-yachtie said:

You said (above) that it was the end of the discussion!

It is.

Share this post


Link to post
Share on other sites
1 hour ago, Colomba said:

Apparently affects yours.

It is.

So authoritative!

Such a turn on. 

Share this post


Link to post
Share on other sites
10 hours ago, Colomba said:

Irrelevant, try again.

Platform is also irrelevant, we’re only talking rig performance here since both rig types works on both platforms. Then again, a platform designed for a wing doesn’t need to withstand any leech, sheet or stay tension...

Fore stay and running back stay tensions together with the mast compression are a fairly big loading on the platform.

Share this post


Link to post
Share on other sites
On 12/7/2019 at 3:12 AM, Kiwing said:

Do you have a wing on your personal boat?  Or crane to lift in on?

Give me a fricking break!  They crane the AC75 boats in and out for every sail and use a crane to install the mast!  Installing a wing sail is just like putting in the mast.

They just wanted to make it look more like a conventional sail, but with the complexity they are building into the sails it makes the wing look like an off the shelf item.  They claim that the sails can be hoisted, but they can't be reefed.  The Italians say the dual sail control was half of the construction cost of their boat.  Unless they can get significant performance with a much simpler system, this dual sail concept is DOA.

  • Downvote 1

Share this post


Link to post
Share on other sites
7 minutes ago, The_Alchemist said:

Give me a fricking break!  They crane the AC75 boats in and out for every sail and use a crane to install the mast!  Installing a wing sail is just like putting in the mast. Not

They just wanted to make it look more like a conventional sail, but with the complexity they are building into the sails it makes the wing look like an off the shelf item.  They claim that the sails can be hoisted, but they can't be reefed.  The Italians say the dual sail control was half of the construction cost of their boat.  Unless they can get significant performance with a much simpler system, this dual sail concept is DOA.

They can drop the sail though. If there is breakage, our conditions get to snotty, they don't need to back the f***ing boat 5 miles back to base. And sideways into the basin. Like OR had to in bda when it got too fresh. And who can forget the great video of bar losing control first of the boat and sail on the crane, and then fully the sail. 

Duh.

Share this post


Link to post
Share on other sites

I would suggest to revisit a SA podcast with Grant Dalton interview.

Among the reasons which lead to the choice of a monohull with mast + sail instead of a cat + wing,

I remember 2:

1-Wind & sea conditions in Kiwiland would have disintegrated the winged cat

2-The "demographics" :Despite teenagers would prefer a cat @ 90% the "demographic" in the sailing clubs shows 80% monohulls.

That is why I am not sure it is relevant to compare the relative merits of these 2 rig concepts.

I don't want to say that when the wise man shows the moon, the simples look at the finger, but it seems to me that the issue mentionned by Terris deserves some attention.

I watched at the apparent wind profile for an-Acat sailing 19 knts in 14knts true wind speed, and it is striking to see how minimal is the ideal twist of the leech

When you look at the formula of a string between 2 points with evenly distributed load,

Well!!! you can see the cost of reducing leech twist with a hudge increased in load .

So I cannot imagine how little (and how big) will be the twist & load on this much longer leech of this double skin sail, with a boat sailing windward at 30 knts in 12 knts true wind for instance. 

Fair wind 

Erwan

Share this post


Link to post
Share on other sites

I looked for a while for the youtube of BAR docking their 45 out with the wing flopping around. Looked a few times can't find. Anyone have an idea where it is?

Thx.

Share this post


Link to post
Share on other sites
10 hours ago, Erwankerauzen said:

I would suggest to revisit a SA podcast with Grant Dalton interview.

Among the reasons which lead to the choice of a monohull with mast + sail instead of a cat + wing,

I remember 2:

1-Wind & sea conditions in Kiwiland would have disintegrated the winged cat

2-The "demographics" :Despite teenagers would prefer a cat @ 90% the "demographic" in the sailing clubs shows 80% monohulls.

That is why I am not sure it is relevant to compare the relative merits of these 2 rig concepts.

I don't want to say that when the wise man shows the moon, the simples look at the finger, but it seems to me that the issue mentionned by Terris deserves some attention.

I watched at the apparent wind profile for an-Acat sailing 19 knts in 14knts true wind speed, and it is striking to see how minimal is the ideal twist of the leech

When you look at the formula of a string between 2 points with evenly distributed load,

Well!!! you can see the cost of reducing leech twist with a hudge increased in load .

So I cannot imagine how little (and how big) will be the twist & load on this much longer leech of this double skin sail, with a boat sailing windward at 30 knts in 12 knts true wind for instance. 

Fair wind 

Erwan

"Among the reasons which lead to the choice of a monohull with mast + sail instead of a cat + wing,"

Not forgetting that the challenger ruled out cats!

Share this post


Link to post
Share on other sites

I think that Bertelli, by ruling out the cats, was expecting a Volvo kind of boat + foils, he did not imagine they would end up with what we have.

  • Like 1

Share this post


Link to post
Share on other sites

2041993166_Leechgap1.thumb.jpg.afcc8f97c24ebd5fb44c12edb47b3fb3.jpgI agree with @barfy here.  I see an almost consistent 100 - 150 mm gap.
This should cause drag should it not? so it must have a great upside somewhere?

Share this post


Link to post
Share on other sites
50 minutes ago, Kiwing said:

2041993166_Leechgap1.thumb.jpg.afcc8f97c24ebd5fb44c12edb47b3fb3.jpgI agree with @barfy here.  I see an almost consistent 100 - 150 mm gap.
This should cause drag should it not? so it must have a great upside somewhere?

If there is airflow through the gap if anything may cause less drag as it may help to keep the air flow attached

  • Like 1

Share this post


Link to post
Share on other sites

The two skins seem to be attached by a 100mm vertical flexible? piece of something (my guess, to account for the consistent gap.)

Share this post


Link to post
Share on other sites
3 hours ago, Kiwing said:

The two skins seem to be attached by a 100mm vertical flexible? piece of something (my guess, to account for the consistent gap.)

I don't really see that. I see a couple of points with maybe something to limit the spread. But a material to keep the skins apart would be difficult to pack down I reckon. Need more pics.

Share this post


Link to post
Share on other sites
12 hours ago, Tornado-Cat said:

I think that Bertelli, by ruling out the cats, was expecting a Volvo kind of boat + foils, he did not imagine they would end up with what we have.

Agreed.  Hard to sugarcoat it. A "Gotcha" for sure.

Fully in the spirit of the DoG.

I have little sympathy for the whingers and hand-wringers who castigate this as a Bridge too Far.

Share this post


Link to post
Share on other sites
5 hours ago, uflux said:

If there is airflow through the gap if anything may cause less drag as it may help to keep the air flow attached

Where does the airflow come from? The luff is continuously connected to the mast by a bolt rope (20.17), there are no open slots or holes allowed in the mast (20.1) or sail (18.1) to let air in. I don't think a gap between the leeches has much of a drag effect (see Kammback), though it might mess with other aerodynamics.

5 hours ago, Kiwing said:

The two skins seem to be attached by a 100mm vertical flexible? piece of something (my guess, to account for the consistent gap.)

Not permitted. Only battens can be connected near the luff by loose lines (presumably to stop the sail doing an impression of a butterfly in a gybe). If the leeches had a continuous connection, that would potentially allow an inflatable sail, which isn't permitted either.

Share this post


Link to post
Share on other sites
2 hours ago, KiwiJoker said:

Agreed.  Hard to sugarcoat it. A "Gotcha" for sure.

Fully in the spirit of the DoG.

I have little sympathy for the whingers and hand-wringers who castigate this as a Bridge too Far.

It was the only reasonable unreasonable choice within the 3 options, the AC will tell if the concept survives or not.

Share this post


Link to post
Share on other sites
5 minutes ago, justsomeone said:

Torsion tube/s for camber/twist control ?

That shot might be leaking info to trained eyes.

PVC with rigging inside?

  • Like 1

Share this post


Link to post
Share on other sites
4 hours ago, RobG said:

Not permitted. Only battens can be connected near the luff by loose lines (presumably to stop the sail doing an impression of a butterfly in a gybe). If the leeches had a continuous connection, that would potentially allow an inflatable sail, which isn't permitted either.

Then how do you account for the visible consistent 100-150mm gap between the two skins at the trailing edges of the two skins?

Share this post


Link to post
Share on other sites
3 hours ago, justsomeone said:

Torsion tube/s for camber/twist control ?

That shot might be leaking info to trained eyes.

One design mast...again

Share this post


Link to post
Share on other sites
6 hours ago, RobG said:

Where does the airflow come from? The luff is continuously connected to the mast by a bolt rope (20.17), there are no open slots or holes allowed in the mast (20.1) or sail (18.1) to let air in. I don't think a gap between the leeches has much of a drag effect (see Kammback), though it might mess with other aerodynamics.

It was interesting to me from the first pics. At first there was a spacer above the hydraulic ram for a meter. Now the lower gap is bigger. Seem to be red telltails to monitor the air flow from the gap. None of It makes much sense as you say. Why maintain the gap when none of the other teams seems to and it seems not to make sense from an aerodynamic point of view, and why put tell tails to monitor exhaust when there is no inlet. I love a mystery.

Share this post


Link to post
Share on other sites

Only the D section shape and a minimum laminate standard are mandated for the mast
Supplied rigging which i thing means shroud and runners

You are free to put any control systems up inside the mast as long as it don't exceed the zone limit.

thus my suggestion of a torsion tube, but could be just containers for the supplied rigging as Ex-yachtie suggested

  • Like 1

Share this post


Link to post
Share on other sites
4 hours ago, Ex-yachtie said:

French text (?). Palma de Mallorca geotag. Is Prada getting a new mast?

French text - suggests travelling through France so could be INEOS on the move..?

Share this post


Link to post
Share on other sites

According to CFD gurus, the "efficiency" of the gap at the footsail sail is not proportionnal to the gap size, expressed as a % of the total span (luff/mast length) :

Dont remember the figures and a bit lazy to check, but AFAIR, viscosity effects start to improve the efficiency when the gap goes lower than 4% of the span.

No idea how many % is 150 mm for this mainsail, but probably less than 1%,

In addition, closing the gap is important in low wind when you need a big lift coeff.

As soon as on the foil, this micro-gap would be probably account for a nano-give-up in induced drag.

Also, when the first ETNZ AC72 started to foil around dec2012 the gap between the main and the deck was not closed, while for the races it was.

So no big reasons to worry, and we must no forget that the guys behind these boats are not in the 2 left hands league.

Cheers

Erwan

 

Share this post


Link to post
Share on other sites
14 hours ago, Ex-yachtie said:

French text (?). Palma de Mallorca geotag. Is Prada getting a new mast?

 

Is this not just exactly what it says, a mast transport bag? Not a new mast

Share this post


Link to post
Share on other sites
57 minutes ago, CaptKeen said:

Is this not just exactly what it says, a mast transport bag? Not a new mast

What's holding the bag up, do you think?

Share this post


Link to post
Share on other sites
5 hours ago, Ex-yachtie said:

What's holding the bag up, do you think?

That tube above it is supporting the bag at about 3 metre spacing.

Share this post


Link to post
Share on other sites
35 minutes ago, Terry Hollis said:

That tube above it is supporting the bag at about 3 metre spacing.

Perhaps Terry.  But do you need a custom articulated heavy duty trailer just for illustrative purposes?

  • Like 1

Share this post


Link to post
Share on other sites
2 minutes ago, KiwiJoker said:

Perhaps Terry.  But do you need a custom articulated heavy duty trailer just for illustrative purposes?

The trailer is nearly 30m long and needs to transport a relatively delicate component, so it's going to be pretty heavy duty anyway. I suppose they traded off a lighter, single purpose build vs something a little heavier that isn't a one trick pony.

I think @Terry Hollis is on the money, the tubes are to suspend the mast in the bag.

Or they're multi–part whisker poles to gull wing the code 0 and jib when it's light…

Share this post


Link to post
Share on other sites
19 minutes ago, KiwiJoker said:

Perhaps Terry.  But do you need a custom articulated heavy duty trailer just for illustrative purposes?

Ha ha ha!

Share this post


Link to post
Share on other sites
4 hours ago, Terry Hollis said:

That tube above it is supporting the bag at about 3 metre spacing.

Surely the mast is in the bag and it's resting on the wooden cradles with Southern Spars logos? The PVC tube again looks to be sat on top of those same chocks with the straps from the bag being used to secure the tube down?

Share this post


Link to post
Share on other sites
40 minutes ago, NZK said:

Surely the mast is in the bag and it's resting on the wooden cradles with Southern Spars logos? The PVC tube again looks to be sat on top of those same chocks with the straps from the bag being used to secure the tube down?

It’s only @CaptKeen who doesn’t think that. 

Share this post


Link to post
Share on other sites

Very interesting Podcast with Greg Johnston from advanced wing systems discussing twin skin set up in the AC boats. He did some work with NYYC and also discusses the rule and trickle down. Bar Karate episode 26

https://podcasts.apple.com/ie/podcast/bar-karate-the-sailing-podcast/id1468993104#episodeGuid=Buzzsprout-2284139

Share this post


Link to post
Share on other sites

Thanks DJ4374,

I would love to hear it, but unfortunatly, when I click on the link, I can't find Greg Johnston name anywhere.

As I am not a digital native, probably I am messing somewhere!  but where ?? I can't say!

That is why anybody's experience is welcome. Thanks in advance.

Cheers

 

Erwan

Share this post


Link to post
Share on other sites
5 minutes ago, Erwankerauzen said:

Thanks DJ4374,

I would love to hear it, but unfortunatly, when I click on the link, I can't find Greg Johnston name anywhere.

As I am not a digital native, probably I am messing somewhere!  but where ?? I can't say!

That is why anybody's experience is welcome. Thanks in advance.

Cheers

 

Erwan

Looks like they havent put it on their website yet, I heard it on the apple podcasts, think it should also be available on Spotify podcasts.

Only went live this morning so Im sure they will update in the next few hours.

Its episode 26.

Share this post


Link to post
Share on other sites

Thanks for the info, I will check on a regular basis, the twin skin sail is an old phantasm for me.

Fair winds and thanks for your relevant infos here or in the Moth universe too.

Cheers

Erwan

Share this post


Link to post
Share on other sites

All this talk on Hull shape - almost 1% category.

Foils also - 2%

But this untalked about twin skin I suspect more than the pair  IMHO.

Share this post


Link to post
Share on other sites
25 minutes ago, Kiwing said:

All this talk on Hull shape - almost 1% category.

Foils also - 2%

But this untalked about twin skin I suspect more than the pair  IMHO.

Agree with your drift, but maybe not your percentages, but you're right the rig/sailplan is critical......don't matter how good everything else is if they ain't enough power driving it all you're farked.

Share this post


Link to post
Share on other sites
4 hours ago, Woolfy said:

Agree with your drift, but maybe not your percentages, but you're right the rig/sailplan is critical......don't matter how good everything else is if they ain't enough power driving it all you're farked.

Easy to copy though so not quite all there, especially the secret ????

It will have to be the month before the match IMHO.

@Woolfy  Just for interest and speculation what would your guess at %s be?

Share this post


Link to post
Share on other sites

Greg Johnston is available, 

Just listen to the first 50mm, Quite easy to understand as Greg speaks clearly enought for a non-English native. I think I could understand around 60%, really a great podcast for wing geekS,

Thanks again DJ4374

Interesting remark regarding the performance windward of a jib+soft wingsail combination

AFAIU, the jib provides better / higher lift due to less parasitic/separation?? on the mast behind, and more interesting:

With a flat jib and larger slot, they sail faster & higher.(To be checked)

Also, as expected, he mentionned that as soon as on the foil, it is only about drag, much enought apparent wind for the lift required.

2 skins + D mast or similar arrangement, almost mandatory to sail high if you don't want the luff to invert behind the mast

The issue is you need power to accelerate and get up on the foil, before to reduce the power

It is very easy with 2 elements hard wingsail on a cat.

Flattening the sail on foiler Moth is mentionned as an illustration of the issue (I feel confident some Mothie sailors will drop a few words about it).

A monohull has not the initial righting moment of a cat, especially with this foiling system.

So each time you go down from the foil and slow down, you will loose more ground than with the AC50 cat.

My "condoleances"  to all Aussies, and feel confident that these guys who managed to take the Cup with Australia II, who brought to the sailing world the 18 skiff, the foiling Moth, among other great "inputs" ....

I feel confident they will make Australia great again

(But for Scott Morisson,... I have no evidence).

Cheers Mates

Erwan

  • Like 1

Share this post


Link to post
Share on other sites
7 hours ago, Kiwing said:

Easy to copy though so not quite all there, especially the secret ????

It will have to be the month before the match IMHO.

@Woolfy  Just for interest and speculation what would your guess at %s be?

I'd be reckoning on 

20% hull, with a 40/40 split between foils and rig.

Share this post


Link to post
Share on other sites

Is end plating the hull to the water a reason for the bustle? LR would be more functional?

@Erwankerauzen Thank you, as always.  What do you think of the secrecy/reveal aspect?  I wonder if we will be able to get very long to talk about the final rig finesse?

@storm petrel suggest a 35 degree tack angle that sounds amazing.  Did I get that right?  Would lead to amazing VMG?

Share this post


Link to post
Share on other sites

Some suitably fuzzy spy pics of ETNZ raising their twin-skin main.

Skins brought together and coupled from two separate piles. 

Looks to me like clips or ties maintaining the gap at each batten (white?), with red tell-tales attached. You can see the batten lines in these shots, before the tension is applied.

main-raise-1.jpg

main-raise-2.jpg

main-raise-4.jpg

  • Like 2

Share this post


Link to post
Share on other sites
46 minutes ago, weta27 said:

Does this show the tie / clip?

main-raise-6.jpg

Are they out today?? That westerly sea breeze is trying to fill in...:mellow:

Share this post


Link to post
Share on other sites
11 hours ago, weta27 said:

Looks to me like clips or ties maintaining the gap at each batten (white?), with red tell-tales attached. You can see the batten lines in these shots, before the tension is applied.

Nice shots. Are the white clips just the termination of the battens? Interesting that Greg Johnson pointed out in the podcast that the skins needed to slide fore and aft, perhaps this is a mechanism for the movement. And also interesting that all the battens, clips?, disappear into one smoothly tensioned leach when sailing. Some serious tension there.

Thx weta, something interesting for a change.

Share this post


Link to post
Share on other sites
11 hours ago, weta27 said:

Does this show the tie / clip?

Funny that the tie between skins looks tensioned down by the red tell tale?  The ties must be clipped in as they pass the boom on the hoist. Very cool.

Share this post


Link to post
Share on other sites

@wind_apparent do you think they could twist the top of the wing to the otherside of the wind in AC35 and if so do you think they will be able to twist the top of this twin skin soft wing  to the other side of the wind?

The fluttering action ETNZ is supposed to have developed in AC35 to use the vacuum on the low pressure side to maximum effect.  Will they be able to use that with the soft sail wing?

Share this post


Link to post
Share on other sites
17 hours ago, wind_apparent said:

@Kiwing I think they could twist the top with a mast head boom plate.... but what do I know. :rolleyes:

I believe some sort of adjudtable sprit would be legal, as long as it could be lowered with the sail. In fact, I’d be surprised if it hasn’t been adopted

Share this post


Link to post
Share on other sites
43 minutes ago, Xlot said:

I believe some sort of adjudtable sprit would be legal, as long as it could be lowered with the sail. In fact, I’d be surprised if it hasn’t been adopted

The AC50s had space for half a dozen rams and control yokes,  imagine it's a lot tougher to invert the top of an independently soft skinned beast. Would be cool but I think that might remain a feature of solid wings.

Share this post


Link to post
Share on other sites

There is some photos suggesting ETNZ might already have it in their soft wings.

Share this post


Link to post
Share on other sites
29 minutes ago, Kiwing said:

There is some photos suggesting ETNZ might already have it in their soft wings.

Sorry I'm not full time here, can you point me in the right direction for these?

Share this post


Link to post
Share on other sites

The top section is free to mess with, pretty sure all the teams have solid sections in there allowing shape and twist  control. 
 

even as far back as when ineos were testing in Spain there were pics of the top section pre set on the tow out before sailing 

Share this post


Link to post
Share on other sites
2 hours ago, JALhazmat said:

The top section is free to mess with, pretty sure all the teams have solid sections in there allowing shape and twist  control. 
 

even as far back as when ineos were testing in Spain there were pics of the top section pre set on the tow out before sailing 

This bit would allow the top control zone to be pre-set, and not have to be detachable in the field.

 

20.19 After sailing, with the mast still stepped in the yacht, the mainsail shall be lowered completely below the
top of the mast lower zone without assistance from anyone who is completely above that zone. This does
not prevent crew going aloft to resolve occasional issues.

Share this post


Link to post
Share on other sites

You're all thinking mechanical manipulation. 

There's other ways to do this. Think harder.

Share this post


Link to post
Share on other sites
14 hours ago, wind_apparent said:

People were wondering what the secondary mast tube was in the mast pictures.

Sorry to interrupt, where can I see the pics with this secondary mast please?

Tkx in advance,

Cheers

 

Share this post


Link to post
Share on other sites

twin mains should be cool as the development will end up on production race boats, solid was a road to nowwhere but the AC and a few other specialised events

  • Like 1

Share this post


Link to post
Share on other sites

This is one of the most interesting areas for me as there quite marked visible differences. 

Why would some of the teams go boomless? Or for that matter hinged I can't really see the advantage vs all the extra control that a more traditional boom gives. You could still have a deck sweeper underneath it so wouldn't lose much. But the ability to control the outhaul separately on the two sails looks like a lot more valuable control to me.

 

But I am sure there are reasons for each of the approaches. Just struggling to remember all the fluid dynamics maths enough to work it out. The impact of the air between the sails is one that is interesting too

  • Like 1

Share this post


Link to post
Share on other sites

There is control structure in the bottom metre + to do the job of a boom so for me who needs a boom?

It is very complex and the booms curve etc.  The trouble is, this is and area that can be still copied so we are not seeing the real solutions?

But I agree the engine is the most interesting place on these boats.  It will see the biggest changes and have the biggest trickle down IMHO.

Share this post


Link to post
Share on other sites
45 minutes ago, enigmatically2 said:

This is one of the most interesting areas for me as there quite marked visible differences. 

Why would some of the teams go boomless? Or for that matter hinged I can't really see the advantage vs all the extra control that a more traditional boom gives. You could still have a deck sweeper underneath it so wouldn't lose much. But the ability to control the outhaul separately on the two sails looks like a lot more valuable control to me.

 

But I am sure there are reasons for each of the approaches. Just struggling to remember all the fluid dynamics maths enough to work it out. The impact of the air between the sails is one that is interesting too

The camber is too great to have a straight boom between the two skins.

The hinged boom would double as the outhaul adjustment: the straighter the boom the more foot tension. Then there are minor adjustments for each skin. 

The idea of a hydraulic hinged boom makes the adjustment of lower camber feel very easy and fast. Also, unlike a boomless option, foot tension is largely independent from leech tension.

  • Like 1

Share this post


Link to post
Share on other sites

If you had a curving trust like structure hidden between the two skins and twin tension hydraulics going to a traveller that might work well?

Share this post


Link to post
Share on other sites

Last year's nats

This year's ongoing as we speak in great conditions in the BOI. Maybe Sam to be un-seated, new yellow jersey today.

Oh, windward can't/heel was the point.

 

SamBullock_2.jpg

Share this post


Link to post
Share on other sites
21 minutes ago, wind_apparent said:

If you had a traveler on the clew and a boom plate that controlled the foot/rotation.. and a rotating wing mast, there is probably no need for a boom, as well as almost sealed end plate, And room to scoot through when switching to trapeze off the other side... 

F481CFCC-B12D-4A64-B612-2541555A138D.jpeg

Is there a database or experience that demonstrates the change in Vortex generation in the area of Leech between where it leaves the deck seal and meets the clew? And how agressive that angle can be before the Vortex flips from deck to clew? Or is it all driven by much more practical matters - such as creating a bigger enough hole for the crew to pass through?

Share this post


Link to post
Share on other sites
4 hours ago, Boink said:

Is there a database or experience that demonstrates the change in Vortex generation in the area of Leech between where it leaves the deck seal and meets the clew? And how agressive that angle can be before the Vortex flips from deck to clew? Or is it all driven by much more practical matters - such as creating a bigger enough hole for the crew to pass through?

There is a coefficient which accounts for the gap between the deck and footsail

It is the Oswald coefficient.

Big velocities differences between windward & leeward side of the sail are on the first/front half of the sail/wing section.

So if the second/rear half of the wing section does not sweep tightly the deck it is not so important,

At the corner between the sailfoot and the deck, separation is likely to occur with the overlap of both pressure distributions.

Nose down sailing provides a negative AoA for the trampoline/deck, I guess it contributes to increase the pressure on both sides of the sail, decreasing negative Cp on the leeward side, hence minimizing the occurence for separation.

Cheers

Share this post


Link to post
Share on other sites
10 hours ago, wind_apparent said:

Like I said. Most of this is from a long ass time ago, and many difficult challenges have happened in my life since I was a boat builder.  I’m mostly just trying to remember my design lexicon right now;  But hard charging.  Finally watching AC34 not long ago, and reading a bunch of Spithill interviews may have literally saved my life.... but now I’m in key west talking to y’all nut jobs.... so... Prada with bullets.... 6.5 creedmoor probably. 

So, which teams AC75 design do you like so far?

Share this post


Link to post
Share on other sites
53 minutes ago, wind_apparent said:

There doesn’t have to be an entrance anywhere on the sail or mast itself I would think; as there is probably a Venturi area somewhere on the leach, and also an exit area. 

Which then raises the issue of the air getting sucked out from between the skins, squeezing the skins together, reducing camber and making it a bitch to trim them independently from one another.

Introducing air at the luff would offset that effect.  In fact, controlling the amount of air that entered at the luff would give you control of the camber; you would be able to inflate the gap between the skins if you wanted to.  Introducing air at different points would enable you to inflate/deflate different part of the sail, all at the expense of drag of course. 

Share this post


Link to post
Share on other sites
2 minutes ago, wind_apparent said:

Who says they are trimming them independently of one another.  It’s more likely they are trimming them in conjunction. 

Videos are showing ETNZ working the outhaul on the skins independently...

Share this post


Link to post
Share on other sites
Just now, wind_apparent said:

How do you know it’s an out haul? :ph34r: because it’s at the clew? 

It’s pretty obvious....:mellow:

Share this post


Link to post
Share on other sites
18 minutes ago, Ex-yachtie said:

Introducing air at the luff would offset that effect.  In fact, controlling the amount of air that entered at the luff would give you control of the camber; you would be able to inflate the gap between the skins if you wanted to.  Introducing air at different points would enable you to inflate/deflate different part of the sail, all at the expense of drag of course. 

Afraid this would be considered as inflatable battens - forbidden

  • Like 1

Share this post


Link to post
Share on other sites
28 minutes ago, wind_apparent said:

So they are pulling on ropes at the clew... must be outhaul. :D

Who said anything about ropes?? Their boom system is hydraulic :rolleyes:

Share this post


Link to post
Share on other sites
1 minute ago, wind_apparent said:

No... it is? :D  like some weird GNav? 

Just carrying on with what was successful in the last cup and integrating it into soft sails. Nothing weird about that. :mellow:

Share this post


Link to post
Share on other sites
1 hour ago, wind_apparent said:

Who says they are trimming them independently of one another.  It’s more likely they are trimming them in conjunction. 

Why wouldn’t you?

Share this post


Link to post
Share on other sites
1 hour ago, Xlot said:

Afraid this would be considered as inflatable battens - forbidden

But the effect already occurs. 
 

Thinking further, the same effect could be achieved through the control of the leeches, and/or the mechanism you join them together. A sealed joint would reduce it significantly whilst a porous fabric would allow a Venturi effect. 

Share this post


Link to post
Share on other sites
5 hours ago, Ex-yachtie said:

Which then raises the issue of the air getting sucked out from between the skins, squeezing the skins together, reducing camber and making it a bitch to trim them independently from one another.

Introducing air at the luff would offset that effect.  In fact, controlling the amount of air that entered at the luff would give you control of the camber; you would be able to inflate the gap between the skins if you wanted to.  Introducing air at different points would enable you to inflate/deflate different part of the sail, all at the expense of drag of course. 

There is this tho:

18.1 Other than as required for sail hardware, intentional openings through sail skins are prohibited. This rule
does not prohibit access panels that are covered or closed whilst racing.

  • Like 1

Share this post


Link to post
Share on other sites
5 hours ago, Ex-yachtie said:

Which then raises the issue of the air getting sucked out from between the skins, squeezing the skins together, reducing camber and making it a bitch to trim them independently from one another.

Introducing air at the luff would offset that effect.  In fact, controlling the amount of air that entered at the luff would give you control of the camber; you would be able to inflate the gap between the skins if you wanted to.  Introducing air at different points would enable you to inflate/deflate different part of the sail, all at the expense of drag of course. 

The sails won't come together. There is air velocity on the outside so lower pressure there. Good old Bernoulli.

They may well trim both together, but it's clear that at least some of the teams can also trim them independently too.