Jump to content

The new sailing twin skin setup


Recommended Posts

  • Replies 2.1k
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

Short straw day in the rigging department  https://www.facebook.com/groups/ViF.Velisti/permalink/10159437643030931/  

When I was landsailing, tactics didn't play as big a role as they do in the America's Cup.  Speed is everything, so it didn't pay to mix it up in close quarters.  The yachts tended to do more of their

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

Posted Images

  • 4 weeks later...

@Lickindip said on ETNZ thread386315537_rotatungleaches.thumb.jpg.94633e1b489911ea7150207283b171b8.jpg

You would have to have the same diameter leach "drum" as the mast to have equal skin distance between skin attachments.
If is "drum" is smaller the lee skin will be in a shorter distance between attachments and have more shape?

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

@Lickindip said on ETNZ thread386315537_rotatungleaches.thumb.jpg.94633e1b489911ea7150207283b171b8.jpg

You would have to have the same diameter leach "drum" as the mast to have equal skin distance between skin attachments.
If is "drum" is smaller the lee skin will be in a shorter distance between attachments and have more shape?

no exactly, the aft 'drum' can be smaller but will have to go through more of an angle rotation to keep the skins the same

below ive got a 400mm wide mast ? (is this correct) rotated 20degrees each way which becomes a 137mm movement

the same movement can be made by a 200mm drum rotating 86 degrees

image.png.ac2d198350aaa66941f201d9f0b186ba.png

i suspect that the attachment points are slightly inside the mainsail and a smaller drum on/ drum off system rotating multiple times could achieve the desired finite control

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

image.png.00bb96f8a46b4dcec95c0ca006f7c6e4.png

If I was going to that much trouble, I'd use separate furlers so tension on each side of the sail is independent. Is this sufficient to control the offset all the way up the sail? Usually outhaul only affects the bottom 1/3rd of the sail, or am I really out of touch with the behaviour and properties of the materials in use?

I also can't see how this would auto–tack, it would need to be adjusted each time.  Maybe there's a setting for offset and they just press a button to reverse it when tacking/gybing.

Link to post
Share on other sites
17 minutes ago, RobG said:

I also can't see how this would auto–tack, it would need to be adjusted each time.  Maybe there's a setting for offset and they just press a button to reverse it when tacking/gybing.

I think they just pull the windward side of the sail as it seems here, and the circular object rotates. I do think they have the same system on the top.

 

Capture.PNG

Link to post
Share on other sites

They have a metre of height above the bottom of the skins, between the skins, in which to hide some clever stuff.  Of course the more simple the fewer problems?

They also have to quickly change the shape of the sails as they accelerate, to quickly change from power to minimum drag?  so simply rotating this drum will quickly change the relative shapes of the skins?

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

I think they just pull the windward side of the sail as it seems here, and the circular object rotates. I do think they have the same system on the top.

Yes, that works for simple drum. A similar system at the top would need a boom–like structure at the head and should extend control to the whole leech. 4 m seems more than enough to fit it in.

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

also can't see how this would auto–tack, it would need to be adjusted each time.  Maybe there's a setting for offset and they just press a button to reverse it when tacking/gybing.

These guys have a track record of smart hydraulics. If you can imagine it, they've prolly evaluated it.

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

 

 

Capture.PNG

Mentioned in another thread, but this is clearly the right place...

 

The attachments tell the story for me.

1/ a ram attached to the traveller with a purchase (hydraulic lines internal to the skins).The ram pushed down on or eases up on the black disk which is attached to the leech of each of the 2 skins above. The disk allows them to move relative to each other but doesn't control their fore and aft movement. That control either comes simply from rotating the mast - or some other hidden device. (The disk gives no impression of being powered 'rotationally' and also does not appear to have any direct attachments that would facilitate moving the skins fore and aft relative to each other as a 'furler' would need to)

2/ an outhaul purchase that attaches to the end of the two deck sweeper battens to control the tension in the foot (feet!?) of the sails

3/ between these two points of tension then is a 'crumple-zone', loser or tighter depending on the settings. It's not designed to look pretty - but to give maximum control/modes while gaining full benefit from deck end-plating.

 

Something like that anyway....need clearer photos.

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

These guys have a track record of smart hydraulics. If you can imagine it, they've prolly evaluated it.

I have no doubt it can be automated, but I don't think that's legal on an AC75. They aren't allowed to have sensors for yacht state, so it would need a human to tell it to do something (which might just be throw a lever or push a port/starboard button). Even a simple drum mechanism still needs a human to tell it to tack for the same reason, it's just simpler. Tacking might be fully automated on a test boat for testing, but not for training.

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

yysw283981.jpg

Quite a bit was said about the LR test boat (launched before their B1) having a forward driving position. Now we know that was just for the test boat. In retrospect it makes a lot of sense—automate everything and just have driver and flight controller for testing and training.

Seems ETNZ had the same idea. There are also a lot of similarities between the aft shapes of the two boats, so while the relationship between the two teams seems to be miles apart now, clearly there was quite a bit of common ground on design early on.

Link to post
Share on other sites
24 minutes ago, RobG said:

I have no doubt it can be automated, but I don't think that's legal on an AC75. They aren't allowed to have sensors for yacht state, so it would need a human to tell it to do something (which might just be throw a lever or push a port/starboard button). Even a simple drum mechanism still needs a human to tell it to tack for the same reason, it's just simpler. Tacking might be fully automated on a test boat for testing, but not for training.

I don't see where sequenced inputs are banned tho? 

Link to post
Share on other sites

they can do what they want with the test boats and with the race yachts outside racing. from memory etnz ac50 B1 was fully controllable from the chase boat and the hydro was powered by batteries while the fake grinders did nothing. they just need to get the illegal gear off the boats for measuring and racing

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

I don't see where sequenced inputs are banned tho? 

As I understand it, §24 Electronic control circuits (ECCs) bans input from anything that can measure yacht state other than the specific sensors mentioned (mostly related to foils and flaps which is reasonable since they're hidden when operating underwater), which they'd need to do for an automated outhaul system to know the boat just tacked. Event sensors that estimate yacht state based on some component within an ECC are banned as inputs (§24.1 (d)), so linking outhaul tacking to say the position of the hydraulic ram that raises or lowers a foil arm, or discharge of the accumulator, is not allowed.

So there is probably an ECC that controls, say, a hydraulic valve and ram to cause the drum to rotate, but it can't be connected to a sensor that detects when the boat tacks, even simple contacts on the mast that activate different circuits if the boom is on port or starboard would likely be out (that's the simplest system I can think of, maybe there are simpler ones).

PS. there is clause 24.1 (a) that allows "passive input devices", but they're defined in §35.87 as requiring the crew to do something such as push a button, move a slider, etc. There's a caveat that yacht movements that cause a crew member to fall onto a passive device causing it to activate is not "measuring yacht state". Someone has a sense of humour.

But of course it's a free for all on the training boat so likely it has fully automated and manual modes. For training a flight controller and helm, you'd want them doing everything manually that they need to do on the real thing, so if one of them is controlling outhaul tacking, they'd want to do that in the training boat. The automated system might be used to find the best settings, sequences, etc. then they're imprinted into human brains through manual training.

(The usual caveat applies: I am not a rules expert!!)

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

they can do what they want with the test boats and with the race yachts outside racing. 

They'd have to be careful not to create a surrogate, for which the definition is very open.

Surrogate Yacht means any yacht exceeding 12m LOA which is capable of producing meaningful design or performance information for use either directly or indirectly in the design, construction or sailing of an AC75 yacht and as further provided in the AC75 Class Rule…

So a modified AC75 might be a surrogate if it's not an AC75, which the protocol defines as:

AC75 Class Yacht means a yacht that complies with or could comply with the AC75 Class Rule;

The "or could" part is very loose, so maybe they can do pretty much anything with B1. But there is also "…whether a yacht is a Surrogate Yacht or not shall be the sole responsibility of the Rules Committee whose decision shall be final."

Glad that's cleared up.

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

As I understand it, §24 Electronic control circuits (ECCs) bans input from anything that can measure yacht state other than the specific sensors mentioned (mostly related to foils and flaps which is reasonable since they're hidden when operating underwater), which they'd need to do for an automated outhaul system to know the boat just tacked. Event sensors that estimate yacht state based on some component within an ECC are banned as inputs (§24.1 (d)), so linking outhaul tacking to say the position of the hydraulic ram that raises or lowers a foil arm, or discharge of the accumulator, is not allowed.

So there is probably an ECC that controls, say, a hydraulic valve and ram to cause the drum to rotate, but it can't be connected to a sensor that detects when the boat tacks, even simple contacts on the mast that activate different circuits if the boom is on port or starboard would likely be out (that's the simplest system I can think of, maybe there are simpler ones).

PS. there is clause 24.1 (a) that allows "passive input devices", but they're defined in §35.87 as requiring the crew to do something such as push a button, move a slider, etc. There's a caveat that yacht movements that cause a crew member to fall onto a passive device causing it to activate is not "measuring yacht state". Someone has a sense of humour.

But of course it's a free for all on the training boat so likely it has fully automated and manual modes. For training a flight controller and helm, you'd want them doing everything manually that they need to do on the real thing, so if one of them is controlling outhaul tacking, they'd want to do that in the training boat. The automated system might be used to find the best settings, sequences, etc. then they're imprinted into human brains through manual training.

(The usual caveat applies: I am not a rules expert!!)

But as in ac35, a button push could sequence say 3 events: like bring traveller to center, change outhaul or leech tension from one skin to the other, then pull the traveller to it's far stop. No sensor needed, all controls just hit a stop and finish. Completely hypothetical example of course, but I think control can stop a ram when it hits the end of travel. 

  • Like 1
Link to post
Share on other sites
On 3/31/2020 at 2:59 PM, Tornado-Cat said:

I think they just pull the windward side of the sail as it seems here, and the circular object rotates. I do think they have the same system on the top.

 

Capture.PNG

If the disc is free to rotate perhaps the sail shape is controlled by mast rotation only

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

But as in ac35, a button push could sequence say 3 events: like bring traveller to center, change outhaul or leech tension from one skin to the other, then pull the traveller to it's far stop. No sensor needed, all controls just hit a stop and finish. Completely hypothetical example of course, but I think control can stop a ram when it hits the end of travel. 

That seems like a grey area to me. Something like "bring traveller to center, change outhaul… then…" sounds like doing things when parts of the yacht are in certain positions, which is measuring or at least estimating yacht state.

An ECC can only use the state of parts within the ECC itself, e.g. when a ram has reached a certain position to stop moving it. Using the fact that you've stopped moving it to then do something else (e.g. turn a drum) is estimating yacht state based on some component within an ECC—"we're stopped the traveller half way, so must be half way through a tack, lets swap the skin tension…".

I think a legal timed sequence would be something like at 0 seconds start moving the traveller, at 0.75 seconds swap skin tension, at 3 seconds lift the foil. The actions are based on timed delays that are manually initiated and just run to completion without reference to whether or not some other action has started or finished, avoiding measurements or estimates of yacht state.

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

They'd have to be careful not to create a surrogate, for which the definition is very open.

Surrogate Yacht means any yacht exceeding 12m LOA which is capable of producing meaningful design or performance information for use either directly or indirectly in the design, construction or sailing of an AC75 yacht and as further provided in the AC75 Class Rule…

So a modified AC75 might be a surrogate if it's not an AC75, which the protocol defines as:

AC75 Class Yacht means a yacht that complies with or could comply with the AC75 Class Rule;

The "or could" part is very loose, so maybe they can do pretty much anything with B1. But there is also "…whether a yacht is a Surrogate Yacht or not shall be the sole responsibility of the Rules Committee whose decision shall be final."

Glad that's cleared up.

sorry I should have said, they can put whatever equipment/controls on B1 and B2 to test sail, if the equipment does not comply with the class rule it must be taken off for measuring /racing ... they cannot build an additional hull over 12m (lets call it B1.5) to test. I think the teams are not allowed to build a 'similar' style of boat where they could gain knowledge for the AC75 except for current racing classes like TP52 and sailgp

for example: the team will have more weather input devices on B1, they will have radio equipment to talk to chase boats, they may have additional electric pumps to make sure they have hydro while evaluating the systems ... all of that would be illegal under the class rule and will be removed for measuring/ official races

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

That seems like a grey area to me. Something like "bring traveller to center, change outhaul… then…" sounds like doing things when parts of the yacht are in certain positions, which is measuring or at least estimating yacht state.

An ECC can only use the state of parts within the ECC itself, e.g. when a ram has reached a certain position to stop moving it. Using the fact that you've stopped moving it to then do something else (e.g. turn a drum) is estimating yacht state based on some component within an ECC—"we're stopped the traveller half way, so must be half way through a tack, lets swap the skin tension…".

I think a legal timed sequence would be something like at 0 seconds start moving the traveller, at 0.75 seconds swap skin tension, at 3 seconds lift the foil. The actions are based on timed delays that are manually initiated and just run to completion without reference to whether or not some other action has started or finished, avoiding measurements or estimates of yacht state.

 

Yes, that's exactly what I was thinking. The timed sequence never knows when you are head to wind, but the overall timing is music that the helmsman and trimmer are dancing to. I believe from below any trimming move can be carried through to completion, or a preset position. There is also some words in the HCC section about manual stops that may be interesting, like a peg board for different modes?

Lovely grey areas.

 

24.1 (e) sensors measuring the internal geometric state of a drive clutch or HCC component, so long as those
sensors do not directly measure yacht state information, and are not used to estimate yacht state
information, for example:
(i) a sensor measuring the orientation of a cam in a hydraulic valve can be measured in order
to drive that cam to a desired position, as long as the orientation of the cam is not used to
estimate pressure or flow; and
(ii) current in a servo motor can be measured as part of a position control loop within the servo
motor circuit, as long as the current is not used to estimate any part of the yacht state, such
as control surface load; but
(iii) a sensor measuring the position of a plunger in a pressure relief valve cannot be measur. 

 

35.108 Yacht state
The specific condition of the yacht, comprising all of the following:
(a) the position and orientation of the yacht in space;
(b) the position and orientation of any control surface;
(c) the position and orientation of a foil;
(d) the position and orientation of any force input device or part thereof;
(e) the stress, strain, tension and force in any part of the yacht, except in passive input devices;
(f) other force-related quantities in any part of the yacht;
(g) the volume, velocity, flow rate or pressure of fluid within, or acting on, any part of the yacht;
(h) all absolute measures of the above and quantities measured relative to each other;
(i) the water or wave height or velocity relative to the yacht;
(j) all time derivatives of the above;
(k) all quantities derived from any of the above; and
(l) all quantities from which the above can be derived or approximated.

Link to post
Share on other sites
On 3/31/2020 at 11:05 AM, nav said:

Mentioned in another thread, but this is clearly the right place...

 

The attachments tell the story for me.

1/ a ram attached to the traveller with a purchase (hydraulic lines internal to the skins).The ram pushed down on or eases up on the black disk which is attached to the leech of each of the 2 skins above. The disk allows them to move relative to each other but doesn't control their fore and aft movement. That control either comes simply from rotating the mast - or some other hidden device. (The disk gives no impression of being powered 'rotationally' and also does not appear to have any direct attachments that would facilitate moving the skins fore and aft relative to each other as a 'furler' would need to)

2/ an outhaul purchase that attaches to the end of the two deck sweeper battens to control the tension in the foot (feet!?) of the sails

3/ between these two points of tension then is a 'crumple-zone', loser or tighter depending on the settings. It's not designed to look pretty - but to give maximum control/modes while gaining full benefit from deck end-plating.

 

Something like that anyway....need clearer photos.

Agreed, we would need better photos and pretty much on your post

I my opinion the ram controls the leach tension while the separated skin are controlled by both the rotation of the mast and the line in the bottom. When the windward line is tensioned it pulls the winward sail and the mast rotates.

However I do not exclude a forced rotation of the black disk which has two lines (rods ?) going toward the top that would control the leach of each sail.

 

Capture.PNG

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

The timed sequence never knows when you are head to wind, but the overall timing is music that the helmsman and trimmer are dancing to. I believe from below any trimming move can be carried through to completion, or a preset position. There is also some words in the HCC section about manual stops that may be interesting, like a peg board for different modes?

Yes, I think that would be OK. There could be sequences for tack, gybe, upwind rounding, downwind rounding, etc. but it's a dangerous gamble if you've been using timed mode all week and suddenly you have to do it all manually, e.g. crash tack to avoid a collision or big gust near a boundary when trying to squeeze the last few metres out of a favourable shift. You also don't want to trigger the wrong sequence!

Maybe not such an issue in a match race where there's only one other boat, but a concern in fleet racing (though maybe there won't be any anyway).

3 hours ago, Lickindip said:

sorry I should have said, they can put whatever equipment/controls on B1 and B2 to test sail, if the equipment does not comply with the class rule it must be taken off for measuring /racing ... they cannot build an additional hull over 12m (lets call it B1.5) to test.

Yes, agree with that.

Link to post
Share on other sites
  • 4 weeks later...

 

  ^ I disagree with their statement that the top control mechanism stays up (and the skins fit into it as they are hoisted). I seem to remember the Rule says it has to come down

 

  • Like 1
Link to post
Share on other sites
9 hours ago, barfy said:

Some observations from the Italian Guy(s).

 

Who are these guys? Are they professionals or just random guys pulling shit out of their asses like the rest of us. Wish Barfy and SClarke had a show like this.

  • Like 1
Link to post
Share on other sites
9 minutes ago, pusslicker said:

Who are these guys? Are they professionals or just random guys pulling shit out of their asses like the rest of us. Wish Barfy and SClarke had a show like this.

Well, Vittorio is Quantum Italy - plus a passionate 12’ Dinghy owner. Don’t recall about the other guy

 

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

Who are these guys? Are they professionals or just random guys pulling shit out of their asses like the rest of us. Wish Barfy and SClarke had a show like this.

Google is your friend...or let me guess...you're one of those who don't Google up shit you see on YouTube...

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

Google is your friend...or let me guess...you're one of those who don't Google up shit you see on YouTube...

I thought you ignored me? It would be a kiwi thing to just keep threatening to ignore  and then continuing the whine forever.

  • Like 1
Link to post
Share on other sites
  • 3 months later...
18 hours ago, Kiwing said:

Here is the thread on sails most of it is in here. This shows the inverted top of the AM sails.1554549109_inverttopAM.thumb.jpg.18c0792a461d19138516173a576ebb3c.jpg

What kind of wind was that in?  With the weird camber changes and twist changes I'm guessing if that sail wasn't battened to hell it would be a full on luff in the main

Link to post
Share on other sites

What is the gap (100mm?) between the skins aft doing?

Must have some venturi effect? but what is its purpose?

Something to do with the unequal overlap?

Who has an idea? I am entirely guessing?

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

What is the gap (100mm?) between the skins aft doing?

Must have some venturi effect? but what is its purpose?

Something to do with the unequal overlap?

Who has an idea? I am entirely guessing?

Been my question all along. No answers, so my guess now is that the gap creates a vacuum that sucks the two skins together.

Link to post
Share on other sites

Yes @barfy I give you the credit for harping on about this gap.

I have been talking to the world 12foot skiff champion who designed his own boats - John Chapple.  He said he designed his 12footer like a 14foot with 2 foot cut off the back.  He said when up and planning the sailed just like a 14 foot.  He won in NZ and Sydney (beat the Aussies at their own game!)

I wonder if the gap acts like a bigger sail meaning the speed off the leech means it acts like those 12 footers, acting like a 14 footer?

Link to post
Share on other sites
On 8/7/2020 at 8:14 PM, barfy said:

Been my question all along. No answers, so my guess now is that the gap creates a vacuum that sucks the two skins together.

So it suck together the second half of the wing, leaving the front teardrop shape?

Link to post
Share on other sites
On 4/2/2020 at 10:31 AM, barfy said:

I believe from below any trimming move can be carried through to completion, or a preset position.

Twice I've seen Te Aihe bail out mid-turn, ie., with both foils in the water, straighten up and end up heading in the opposite direction - surely that would be dangerous if the sequences were set to go all the way once initiated?

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

Twice I've seen Te Aihe bail out mid-turn, ie., with both foils in the water, straighten up and end up heading in the opposite direction - surely that would be dangerous if the sequences were set to go all the way once initiated?

True, but they all would have a panic button. You're probably watching practice of a " this will screw them up" starting manoeuvre.

Any smart toolmaker creates "macros" for sequences that you do many times over. Who knows, maybe a longer press on the sequence button adjusts timing?

Link to post
Share on other sites
  • 3 weeks later...

I still believe these wings/sails will be the winning of the cup.

Yes the foils will make a difference but because of the "choose them a few days ahead" they will be close to the same in performance.

Now the sails are new beasts and you have lots of choice.  There will be 10% difference in performance between the best and the worst?

JUST MY OLD MAN belief!

  • Like 2
Link to post
Share on other sites
7 minutes ago, Kiwing said:

I still believe these wings/sails will be the winning of the cup.

Yes the foils will make a difference but because of the "choose them a few days ahead" they will be close to the same in performance.

Now the sails are new beasts and you have lots of choice.  There will be 10% difference in performance between the best and the worst?

JUST MY OLD MAN belief!

Interesting perspective, re foils and advanced foil configuration choices.

What characteristics do you think will distinguish the various wings? 

Speed of adjustment, max camber range, max twist range, minimum drag at the mast tube, lowest induced drag, lowest mass aloft,  best end plating.. any others?

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

I still believe these wings/sails will be the winning of the cup.

Yes the foils will make a difference but because of the "choose them a few days ahead" they will be close to the same in performance.

Now the sails are new beasts and you have lots of choice.  There will be 10% difference in performance between the best and the worst?

JUST MY OLD MAN belief!

I kinda agree, given all those variables and the complexity in them.  But then the limiting factor on top speed seems to be the foils.

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

I kinda agree, given all those variables and the complexity in them.  But then the limiting factor on top speed seems to be the foils.

Be great for the event if they were all within a gnats whisker of each other speed wise and it came down to good old fashioned sailing skills like tactics and crew work.

I'll keep dreaming shall I...

 

  • Like 2
Link to post
Share on other sites
20 minutes ago, Teaky said:

 But then the limiting factor on top speed seems to be the foils.

Don't forget rig drag too, Teaky. That will be massive at those top-end, AWSs

  • Like 1
Link to post
Share on other sites

have to agree with the sails being an almost forgotten part of this

foils that cavitate earlier than others can be compensated by going for more vmg and less speed

 

sails that dont have enough power have no such alternative

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

I still believe these wings/sails will be the winning of the cup.

Yes the foils will make a difference but because of the "choose them a few days ahead" they will be close to the same in performance.

Now the sails are new beasts and you have lots of choice.  There will be 10% difference in performance between the best and the worst?

JUST MY OLD MAN belief!

Good, then you agree with the design teams.  In the Shirley Robertson's podcast with the AC75 designers they said the same thing.  That since the foils will be fixed before the weather reports, they will have to learn to trim the sails for the changing conditions.

Link to post
Share on other sites
35 minutes ago, Varan said:
40 minutes ago, Sailbydate said:

Don't forget rig drag too, Teaky. That will be massive at those top-end, AWSs

Please explain. 

A while back, ETNZ team member and North Sails designer, Burns Fellow was talking about the aerodynamic forces on the AC75 rigs. He was saying, "drag becomes a very important consideration when you have 45-50kts of apparent wind coming across the deck.” 

It's a whole different ball game to displacement hull upwind sailing, where 12 knots is positively honking, apparently. ;-)

 

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

Interesting perspective, re foils and advanced foil configuration choices.
What characteristics do you think will distinguish the various wings? 
Speed of adjustment, max camber range, max twist range, minimum drag at the mast tube, lowest induced drag, lowest mass aloft,  best end plating.. any others?

for this 75yrold laser sailor.
1) Max power to get them onto the foils in next to no wind and ASAP.
2) Speed/control of shape change to minimum drag.
3) Ability to drop the centre of effort for VMG.

But no one has given us a satisfactory reason for the 100mm gap between the leeches that @barfy pointed out.  Seems puzzling?

  • Like 1
Link to post
Share on other sites
1 hour ago, Kiwing said:

But no one has given us a satisfactory reason for the 100mm gap between the leeches that @barfy pointed out.  Seems puzzling?

Regarding the twin leeches, Burns Fellow is on record as saying, "... the mainsail has two skins and when you are going from one tack to the other, the leeches won't align with each other. For the sail to assume its correct sectional shape, you need to have more camber on one side than the other.”

According to the Sail-World article, a key to achieving a homogenous surface is the way in which the mainsail skins attach to the D-shaped wingspar – and similarly at the leech where the options are to have the two skins attached or connected in some way to each other, or for the two skins to be completely independent of each other. Says Fellow, “In the rule, there are two specific zones - near the mast and near the leech - where we have left it up to the teams to have a lot of design control as to how they attach the sail (to the mast) or connect the skins (at the leech)... It is over to the teams to control the sails as they wish.”

It's an old article, but a goodie: https://www.sail-world.com/news/214640/Americas-Cup-AC75-rig-concept-took-20-minutes

Bolding mine.

 
  • Like 1
Link to post
Share on other sites

Thanks bestbeforedate.

However my observation - correct me if I'm wrong - is that the leaches are help separate by exactly the same all the way up.  Given the differing width of the sail from top to bottom the same gap all the way up must be for a non-obvious (but important?) reason?

My mates suggestion of creating a vacum to keep the flow attached and to create low pressure inside the wing? Who knows?

Opinions please.

 

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

Thanks bestbeforedate.

However my observation - correct me if I'm wrong - is that the leaches are help separate by exactly the same all the way up.  Given the differing width of the sail from top to bottom the same gap all the way up must be for a non-obvious (but important?) reason?

My mates suggestion of creating a vacum to keep the flow attached and to create low pressure inside the wing? Who knows?

Opinions please.

I think the space between the leaches is quite deliberate, if you compare two aerofoil shapes with the same chord depth and the same length but one is notionally longer but has the tail cut back as is the case with many motor cars.

The longer notional length will be a lower drag than the version with a sharp tail.  This seems quite common at the relatively low wind velocities compared to aircraft.

Link to post
Share on other sites

OK. Yes, it seems we are. But here's what I think. The leech gap is largely closed, when the outhauls are tensioned up. This would also be consistent with the D section mast rotating to windward, if you think about the inside of each skin out the maximum outhaul position. See these two pics of Defiant as an example of this theory.

Thoughts?

decksweeper1.thumb.jpg.b1b5124aadf8361cd34a1b9c81214cbc.jpg.7d9ffe18e4731b7999672752bb4837e2.jpg

Capture.PNG.da9855267a4c56f35a66fcbf72b75096.PNG

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

OK. Yes, it seems we are. But here's what I think. The leech gap is largely closed, when the outhauls are tensioned up. This would also be consistent with the D section mast rotating to windward, if you think about the inside of each skin out the maximum outhaul position. See these two pics of Defiant as an example of this theory.

Thoughts?

decksweeper1.thumb.jpg.b1b5124aadf8361cd34a1b9c81214cbc.jpg.7d9ffe18e4731b7999672752bb4837e2.jpg

Capture.PNG.da9855267a4c56f35a66fcbf72b75096.PNG

leech looks open to me when power is on. when the sail is luffing they let it sag together.

 

1 hour ago, Terry Hollis said:

think the space between the leaches is quite deliberate, if you compare two aerofoil shapes with the same chord depth and the same length but one is notionally longer but has the tail cut back as is the case with many motor cars.

i agree with the first sentence. but can't make head or tails of your second. could you use some pictures?

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

Thanks bestbeforedate.

However my observation - correct me if I'm wrong - is that the leaches are help separate by exactly the same all the way up.  Given the differing width of the sail from top to bottom the same gap all the way up must be for a non-obvious (but important?) reason?

My mates suggestion of creating a vacum to keep the flow attached and to create low pressure inside the wing? Who knows?

Opinions please.

 

me ? shucks. a vacuum is the only reason i can see to spend huge effort in keeping the gap when it would be so easy to close it. Haven't kept track of the other two teams , would be nice to see a comparison.

i've been banging on about this since day one with no input.

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

OK. Yes, it seems we are. But here's what I think. The leech gap is largely closed, when the outhauls are tensioned up. This would also be consistent with the D section mast rotating to windward, if you think about the inside of each skin out the maximum outhaul position. See these two pics of Defiant as an example of this theory.

Thoughts?

decksweeper1.thumb.jpg.b1b5124aadf8361cd34a1b9c81214cbc.jpg.7d9ffe18e4731b7999672752bb4837e2.jpg

Capture.PNG.da9855267a4c56f35a66fcbf72b75096.PNG

It seems to me that in the first case we can see both skins from the angle of the shot, while in the second we cannot.

Look under the boom to see how far forward the skin away from camera is relative to the near-side one. 

Where you have an angle that let's you see them both you see the gap - otherwise not.

If the skins have separate outhauls tracks it makes it hard to get them really close to each other. (Obviously they need to move fore and aft relative to each other)

Having them both attached to a rotating hydraulic mechanism, might give a different result. Have we seen that on ETNZ boats?

Link to post
Share on other sites
10 minutes ago, Frogman56 said:

If it is 100 mm, it is nearly irrelevant. About the same as the squared off trailing edge of a keel, say ok at 5mm on a  mid size keelboat? (Reynolds number wise)

On a related subject, what’s the purpose of the black stripe one sees on the trailing edge of Nacra 17 daggerboards?

Link to post
Share on other sites
42 minutes ago, nav said:

It seems to me that in the first case we can see both skins from the angle of the shot, while in the second we cannot.

Look under the boom to see how far forward the skin away from camera is relative to the near-side one. 

Where you have an angle that let's you see them both you see the gap - otherwise not.

If the skins have separate outhauls tracks it makes it hard to get them really close to each other. (Obviously they need to move fore and aft relative to each other)

Having them both attached to a rotating hydraulic mechanism, might give a different result. Have we seen that on ETNZ boats?

The pics show the boat on different tacks, that why the trim on the main looks different. Look at the spray as well as the helm/crew positions 

  • Like 1
Link to post
Share on other sites
1 hour ago, nav said:

It seems to me that in the first case we can see both skins from the angle of the shot, while in the second we cannot.

Look under the boom to see how far forward the skin away from camera is relative to the near-side one. 

Where you have an angle that let's you see them both you see the gap - otherwise not.

If the skins have separate outhauls tracks it makes it hard to get them really close to each other. (Obviously they need to move fore and aft relative to each other)

Having them both attached to a rotating hydraulic mechanism, might give a different result. Have we seen that on ETNZ boats?

ETNZ shows some gap when not  sailing, but I can't recall if there's been a good pic up close while they're on the foil. They do have 3 hoses going to the aft end of their boom, which I've never been  able figure since there's the one big gimballed ram for the sheet.

Link to post
Share on other sites

Seems like a fore-aft gap is different from a side-to-side gap and it's hard to tell the difference in a photo. The first comes as a result of the angle of the mast and the shape of the air foil they are making. The latter I am guessing is just due to practical limits, but perhaps also has to do with shape, chord, efficiency, and that noise/drag consideration when you have a foil that is too sharp.

  • Like 1
Link to post
Share on other sites
8 hours ago, JALhazmat said:

The pics show the boat on different tacks, that why the trim on the main looks different. Look at the spray as well as the helm/crew positions 

Not relevant. They are different mainsails too, but that's not the point. If you look at the outhaul measurements on the boom (same boom in both pics)  - that's where the trim makes a difference to the leech slot, IMO.

  • Like 1
Link to post
Share on other sites
4 minutes ago, Sailbydate said:

Not relevant. They are different mainsails too, but that's not the point. If you look at the outhaul measurements on the boom (same boom in both pics)  - that's where the trim makes a difference to the leech slot, IMO.

I agree @Sailbydate the two pictures show vastly different leech separation. So we will see which AM prefers in the coming weeks?

Link to post
Share on other sites

I think ETNZ and AM have two completely different systems.

AM's two leeches slide past each other on parallel tracks on top of the boom - the "gap" you can see is length-wise, not width of separation.

The windward leech will always be further back on the boom as the windward skin is flatter, ie., has less camber.

The above photos are on different tacks - the first shows the "gap" because the windward leech is extending past the leeward leech.

On the opposite tack, the closer windward leech is longer, so you can't see the leeward leech at all.

ETNZ's system appears to maintain a close and consistent connection between the leeches, and a small but controlled gap. 

So maybe ETNZ's system adjusts for the differences in windward/leeward skin movement at the mast end??

  • Like 4
Link to post
Share on other sites
2 minutes ago, weta27 said:

I think ETNZ and AM have two completely different systems.

AM's two leeches slide past each other on parallel tracks on top of the boom - the "gap" you can see is length-wise, not width of separation.

The windward leech will always be further back on the boom as the windward skin is flatter, ie., has less camber.

The above photos are on different tacks - the first shows the "gap" because the windward leech is extending past the leeward leech.

On the opposite tack, the closer leeward leech is longer, so you can't see the windward leech at all.

ETNZ's system appears to maintain a close and consistent connection between the leeches, and a small but controlled gap. 

So maybe ETNZ's system adjusts for the differences in windward/leeward skin movement at the mast end??

for the Americans, Thank you! you summed up the relative movement of the windward skin in relation to the leeward on each tack  perfectly
 

just waiting for you to be told it’s irrelevant now too ;-) 

 

 

  • Like 1
Link to post
Share on other sites
6 minutes ago, weta27 said:

On the opposite tack, the closer leeward leech is longer, so you can't see the windward leech at all.

So you're saying camera angle is hiding the gap, which is still there, Weta? Ahem. Back on your rock, mate. ;-)

Link to post
Share on other sites
1 minute ago, weta27 said:

Yup, gap is still there, but on the other side.

Sorry SBD, venturing outside my duty brief, I know!

Just looking for some clarity, Weta. Appreciate the input. And the pics, as always.

Link to post
Share on other sites

Guys does AM have a gap, across the boom, of about 100mm?  I realize each leech moves forward and back along the boom and this confuses the observation but it still seems to me that the 100mm gap is there between the leeches across the boom.  It might be more when measured leech corner to leech corner, when one moves 100mm forward relative to the other? but across between the tracks the leeches slide in it must be about 100mm?

Link to post
Share on other sites
22 hours ago, Sailbydate said:

Don't forget rig drag too, Teaky. That will be massive at those top-end, AWSs

Martin Fisher said in the Shirley R podcast that aero drag will be roughly 50% of overall drag, surprised me. 

Link to post
Share on other sites
1 hour ago, weta27 said:

There's got to be a reasonable gap for the two cars and various attachments to slide freely past each other.

Hypothetically, the car slots could be divergent and not necessarily parallel. It's a pretty wide boom section on Defiant. But I wouldn't have a clue if they'd even WANT to close the gap, so probably a croc. Who knows.

  • Like 1
Link to post
Share on other sites

I’m guessing the booms in the Match will have two ‘elastic’ above and below boom sections. And at 40 knots upwind, 50 downwind, the trimming will be (like with how Gashby so brilliantly did it in Bermuda) more refined, leech twist touches, than in traveler movement. 
 

The software (Xbox-like) is going be almost as big a competition this time as the hardware. 

Link to post
Share on other sites
9 hours ago, Stingray~ said:

The software (Xbox-like) is going be almost as big a competition this time as the hardware. 

you call yourself a SW dev guy.

WTF is software(x-box like)??? video games drive real time animated 3D graphics, nothing at all like this application.

Link to post
Share on other sites