Tornado-Cat

Boats and foils comparison

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8 minutes ago, phill_nz said:

 

very true

 

whatever the future holds

the defender will be using a plain t foil and the challenger a bulb foil

Nothing is for sure. 6 design iterations, and diversion...nothing is certain until the first race of the Match.

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1 hour ago, Herfy said:

 

mule American-Magic-Flying.jpg

This image captures the exact moment AM were inspired to build (untitled) goose foils.

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2 hours ago, Herfy said:

 I am only pointing out that all of the other teams have already tested the type of foils on NZ (minus some wing tips).  They have ALL gone to the bulb type.  

NZ may have simulated something on that foil type that the others have not seen in calculations or testing, but I would doubt it.  

Every pre-release AC75 design drawing and promotional efforts show the NZ type of foils.  Do you really think that ALL three of the other teams missed some iteration of that foil type?  UK spent at least 90,000 man hours into just the design of their B1.

 

 

 

 

 

So what you’re saying is that no one has trialed the bulb approach in reality. Now they’re all using them?

I think this reinforces the idea that the bulb is for testing wings. The test boats had no constraint here and the challengers have figured out that wings are important.

If I was to put money on one team to get it right, out of the box, based on previous performance, I’d put it on Team New Zealand. 

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1 hour ago, Herfy said:

Based upon the history of the foils used in the other three camps, I would say that there is at least a 75% chance that NZ f'd up.

Based on the history of the other three camps, I would say there’s a 75% chance that Team New Zealand know what they’re doing better than the other three put together. 

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5 minutes ago, Ex-yachtie said:

So what you’re saying is that no one has trialed the bulb approach in reality. Now they’re all using them?

I think this reinforces the idea that the bulb is for testing wings. The test boats had no constraint here and the challengers have figured out that wings are important.

If I was to put money on one team to get it right, out of the box, based on previous performance, I’d put it on Team New Zealand. 

No, that is not what I said.  I said they have all tried wing foils like NZ is using and have changed to the bulb.  As was pointed out earlier, AM used bulb foils on the mule, and we do not know all the types of foils that the teams used on the test boats.  There is no limit on how many they can run on the test boats.

All of those that look at the bulb foil as just a test foil, or a way they can make several variations within the rule are missing the boat.  The bulb foils are being used because those teams feel that they are a better design for the performance that they require.  Yes, they could make more changes to the foil arms, but that is not the sole reason for choosing the bulb design.

NZ has a very good track record on foil design, but if all of your competitors have moved away from the style that you have chosen, then it may be time to worry.  Remember, the NZ blade design is what was mocked up on the original designs and it is what everyone of the 3 test boats started to use when they started to sail.  All of these teams are very familiar with the thin foils that NZ used in the last cup.

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10 minutes ago, Ex-yachtie said:

Based on the history of the other three camps, I would say there’s a 75% chance that Team New Zealand know what they’re doing better than the other three put together. 

Now that is flat out homeboy thinking.  I am not trying to attack NZ, just pointing out an obvious fact.  We do not really know yet which design is better, but if 3 of the 4 super teams with well over 150,000 man-hours of design have chosen the same "out of the box" approach, then it may have some merit.  Hey, I would be thinking the same thing if it were AM that was the odd team out.

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24 minutes ago, Herfy said:

Now that is flat out homeboy thinking.  I am not trying to attack NZ, just pointing out an obvious fact.  We do not really know yet which design is better, but if 3 of the 4 super teams with well over 150,000 man-hours of design have chosen the same "out of the box" approach, then it may have some merit.  Hey, I would be thinking the same thing if it were AM that was the odd team out.

Have you worked out how many thousands of man-hours Team New Zealand proved wrong last time, by a considerable margin?

 

The fact remains, if I were to trust any one team to design foils, it would be them. 

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On 10/4/2019 at 12:56 AM, Monkey said:

Turn it upside down. AM’s hull shape is remarkably wing shaped, just upside down producing downforce instead of lift. That downforce increases righting moment, thus increasing power. 
 

That’s all just my theory. 

and quite an intriguing theory it is too!

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LR looking like they have a trick boom and main shaping system (LR thread). Who thought so many major differences with only 4 teams. Can see things evolving up until the last race. Brilliant. 

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It is not clear to me if the six foil limit applies to each boat or each team.  The challengers can build two boats but can only sail one at a time so six per team seems reasonable but the defender will be sailing two boats together so six foils would be a serious limitation for them.

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1 hour ago, Herfy said:

All of those that look at the bulb foil as just a test foil, or a way they can make several variations within the rule are missing the boat.  The bulb foils are being used because those teams feel that they are a better design for the performance that they require.  Yes, they could make more changes to the foil arms, but that is not the sole reason for choosing the bulb design.

And it is an intriguing hypothesis, the Italian you tube brothers came up with it I believe.

Still not backed up by any real reporting I believe. And I still have a logical problem that it would put all of your foil wing tests in the same corner, that of stubby low aspect wings with a big ass bulb. You would exclude all the longer high aspect ratio designs. As the brief calls for an all around design this seems like a bad choice.

And I'm not saying that etnz didn't get it wrong, or right, just that the current reasoning around the reason du bulb seems speculative.

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GD said at the launch that the boat was out there and would be very difficult to sail. As far as I can recall all the early crashes we've seen on the test boats have been using the long skinny foils not the bulbed version. 

Seems to me that there's a strong probability the the bulbed foils are making the boats easier to sail, but is this at the expense of speed?

ETNZ could well be taking a "fuck it we'll get wet a few times whilst we get our heads around sailing the boat and not the simulator, but we'll be fast when we get there" attitude whilst the others are using "training wheel" type foils in the first instance, planning to move over to faster but less stable foils once they've got a bit more experience. It should be remembered that whilst they've had a few splashdowns ETNZ have not had any big wipeouts and from what I've been told the boat has just picked herself and carried on trucking after the splash, they really haven't lost that much speed.

It'll be interesting to see whether after a few weeks sailing these things the bulbs get smaller or disappear of whether ETNZ grows some. Six foils is actually quite a lot to play with when you consider that alterations are permitted and changing the flaps can effectively give you a completely different overall foil shape.

I don't think any team has painted itself into a corner yet.

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2 hours ago, Terry Hollis said:

t is not clear to me if the six foil limit applies to each boat or each team.  The challengers can build two boats but can only sail one at a time so six per team seems reasonable but the defender will be sailing two boats together so six foils would be a serious limitation for them.

 

5 Component limits and modifications
5.1 The components in the table below are restricted as detailed in the following rules:
Component Rule Quantity Change allowance
Hull surfaces Open 2 y 0% & 25% area
Foil arms Supplied 4 -
Foil arm trailing edges Open 6 20% mass
Foil wings Open 6 20% mass
Foil flaps Open 20 20% mass
FCSs Supplied 2 -
Rudder uppers Open 4 20% mass
Rudder lowers Open 4 20% mass
Mast tubes Specified 3 20% mass
Supplied rigging sets Supplied 3 -
Mainsails Open *10 25% area
Headsails Open *29 25% area
yWith reference to the Protocol, a Competitor may modify one of its hulls but not the other.
*See Rule 5.11.

 

https://drive.google.com/file/d/1jlbGdGZ-XERd63SGESoMamTgGZdRiPZJ/view

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1 hour ago, Woolfy said:

Seems to me that there's a strong probability the the bulbed foils are making the boats easier to sail, but is this at the expense of speed?

My thinking too. And the logic could support that theory - challengers started out with ETNZ flat foils and couldn't control their test boats, so developed torpedo versions for better control. As good as any theory put up so far, IMO.

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so we get what

trained huskies v a drunk greyhound

 

so .. its up to flipper to figure out how sober she can get

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4 hours ago, phill_nz said:

 

5 Component limits and modifications
5.1 The components in the table below are restricted as detailed in the following rules:
Component Rule Quantity Change allowance
Hull surfaces Open 2 y 0% & 25% area
Foil arms Supplied 4 -
Foil arm trailing edges Open 6 20% mass
Foil wings Open 6 20% mass
Foil flaps Open 20 20% mass
FCSs Supplied 2 -
Rudder uppers Open 4 20% mass
Rudder lowers Open 4 20% mass
Mast tubes Specified 3 20% mass
Supplied rigging sets Supplied 3 -
Mainsails Open *10 25% area
Headsails Open *29 25% area
yWith reference to the Protocol, a Competitor may modify one of its hulls but not the other.
*See Rule 5.11.

 

https://drive.google.com/file/d/1jlbGdGZ-XERd63SGESoMamTgGZdRiPZJ/view

Thank you for that, the later version of the rule (version 1.1) is a little different but does not seem to account for the needs of the defender when he is sailing both boats..

5 Component limits and modifications
5.1 The components in the table below are restricted as detailed in the following rules:
Component Rule Quantity Change allowance
Hull surfaces Open 2 As per Protocol
Foil arm stocks Supplied 4 -
Foil arm fairings Open 6 20% mass
Foil wings Open 6 20% mass
Foil flaps Open 20 20% mass
FCSs Supplied 2 -
Rudder uppers Open 4 20% mass
Rudder lowers Open 4 20% mass
Mast tubes Specified 3 20% mass
Supplied rigging sets Supplied 3 -
Mainsails Open *10 25% area
Headsails Open *29 25% area
*See Rule 5.8.

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8 hours ago, Sailbydate said:

My thinking too. And the logic could support that theory - challengers started out with ETNZ flat foils and couldn't control their test boats, so developed torpedo versions for better control. As good as any theory put up so far, IMO.

You are making assumptions that favor your bias that not supported by the facts.  The test boats were the first ever of this design and they pushed them to the limits.  All of the test boats were able to sail under control for extended periods of time on the "wing foils".  AM said the boats were fairly stable when up and foiling.  The problems were in sailing in displacement mode and the transitions between displacement and foiling.  The "variable keel" quickly shifts the RM depending upon the mode of sailing.  

The bulb foils, with a concentrated mass, allows the crew to precisely adjust the RM quickly as it is needed during transition periods or wind shifts.

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11 minutes ago, Herfy said:

The bulb foils, with a concentrated mass, allows the crew to precisely adjust the RM quickly as it is needed during transition periods or wind shifts.

What a pile of rubbish.  The shape/form of the wings/bulb has no effect on how quickly the foil arms can be adjusted.

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10 hours ago, barfy said:

And it is an intriguing hypothesis, the Italian you tube brothers came up with it I believe.

Still not backed up by any real reporting I believe. And I still have a logical problem that it would put all of your foil wing tests in the same corner, that of stubby low aspect wings with a big ass bulb. You would exclude all the longer high aspect ratio designs. As the brief calls for an all around design this seems like a bad choice.

And I'm not saying that etnz didn't get it wrong, or right, just that the current reasoning around the reason du bulb seems speculative.

I agree this is not a settled issue; for one thing, a bulb is not the only way to centralize the mass and then modify with abandon. A thick T or Y, with mass up to the stock arm and along the wings in the region of max thickness could also be used. It wouldn't even lock down the angle of intersection of the foil wings and the arm, because you could theoretically recast the junction of the three with the existing outboard pieces in the tooling, if you didn't want to rely on welds, etc. 

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1 hour ago, Herfy said:

 

The bulb foils, with a concentrated mass, allows the crew to precisely adjust the RM quickly as it is needed during transition periods or wind shifts.

But at what cost to drag?

And I've not seen Flipper spinning out or flopping over (yet). Maybe your bias is as unsupported as mine, Herfy? ;-)

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1 hour ago, Ex-yachtie said:

What a pile of rubbish.  The shape/form of the wings/bulb has no effect on how quickly the foil arms can be adjusted.

I wasn't thinking that the foil arms can be moved faster.  I was thinking about better control of the center of mass, which doesn't make sense the more i think about it.  Well, nevermind...lol

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5 minutes ago, Herfy said:

I wasn't thinking that the foil arms can be moved faster.  I was thinking about better control of the center of mass, which doesn't make sense the more i think about it.  Well, nevermind...lol

Mate. That's quite enough self-flagellation. It's our job to debate the counter arguments! :-)

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6 hours ago, Tornado-Cat said:

Best article so far on comparing Manta with the other boats.

I dont't agree with one point, I think Ineos tried to maximise the beam thanks to their vertical sides.

https://www.sail-world.com/news/222778/Americas-Cup-Analysis-of-INEOS-Team-UK-AC75

INEOS absolutely maximised beam, it's not just the vertical sides, but also the fact the foil mounts are basically inside the hull, the mounts are part of a one design piece of kit that is a set width.

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2 hours ago, Stingray~ said:

1E2DAE8B-6F78-491E-96FA-BA963FF826BF.thumb.jpeg.6ec5278c28ed0100899a81eb99a59cf5.jpeg66A94A42-4E52-49EA-BCE0-D547087DC08A.thumb.jpeg.988b708718ac9cb87fbe4b3f42c4c221.jpeg

LR without the skeg looks quite similar to AM and Ineos underneath. will be interesting if the latter two move that way in B2

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it looks like hard touch downs are a "thing "

so who has the best entry and bounce back to slow down the shock and keep some directional stability

the surfboard shapes of AM and IN look like a hard hit and bounce ( which could slew it in any direction )

the softer entries of LR and NZ look like helping to keep the boat straight as they bounce back

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7 minutes ago, phill_nz said:

it looks like hard touch downs are a "thing "

Maybe there will be less of them after another week of sailing the boats. 

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2 hours ago, Boybland said:

INEOS absolutely maximised beam, it's not just the vertical sides, but also the fact the foil mounts are basically inside the hull, the mounts are part of a one design piece of kit that is a set width.

We agree, they also maximised the beam as far as possible to the stern. They may want to get max RM to gain speed and foil.

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29 minutes ago, phill_nz said:

the surfboard shapes of AM and IN look like a hard hit and bounce ( which could slew it in any direction )

the softer entries of LR and NZ look like helping to keep the boat straight as they bounce back

The skipping stones in some video posted somewhere suggests a rock with a rounded underside has the sweetest skip. As we all know. 

The boats boats be spinning like a rock but there will be some degree of yaw and you’d want a smooth bottom in that case too.

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26 minutes ago, barfy said:

Maybe there will be less of them after another week of sailing the boats. 

By early ‘21 they will be flying 99% of the time. The trick is to get liftoff first and then fly the fastest!

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38 minutes ago, phill_nz said:

it looks like hard touch downs are a "thing "

so who has the best entry and bounce back to slow down the shock and keep some directional stability

the surfboard shapes of AM and IN look like a hard hit and bounce ( which could slew it in any direction )

the softer entries of LR and NZ look like helping to keep the boat straight as they bounce back

A V hull allows a softer entry while a flat hull makes a harder impact. However if the boat is fast, the hull that penetrates the water will decelerate and create a crash while the flat hull skips without losing much speed.

So in fact, a flat hull make be less dangerous for the crew, unless they hit big waves, in that case a V hull is softer. I would personally go for the flat rounded hull.

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they will be sailing in the auckland chop

its not always in a constant direction

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consider

if a boat hits with one side before any directional control has entered

even a small 10 deg change of direction will have consequences ( esp at 25knts plus )

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59 minutes ago, phill_nz said:

it looks like hard touch downs are a "thing "

so who has the best entry and bounce back to slow down the shock and keep some directional stability

the surfboard shapes of AM and IN look like a hard hit and bounce ( which could slew it in any direction )

the softer entries of LR and NZ look like helping to keep the boat straight as they bounce back

No doubt in my mind that INEOS UK has been designed as a GEV (ground effect vehicle). Think about it....

These “boats” will be on foils virtually all of the time. And ground effect advantages helps them stay that way, and more stable as well. The hull itself is a “wing” with side fins to guide/redirect airflow.

https://en.wikipedia.org/wiki/Ground-effect_vehicle

https://www.dedoimedo.com/physics/ekranoplans.html

 

502272D2-B0CE-4F9E-85E5-A529BB6CB8E6.jpeg

F64AC301-09C9-4887-8159-14223F20EB20.jpeg

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7 minutes ago, phill_nz said:

consider

if a boat hits with one side before any directional control has entered

even a small 10 deg change of direction will have consequences ( esp at 25knts plus )

If your ‘keel’ is not perfectly aligned with your direction when you touch down, you’re gonna be f’d at 50 knots..

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1 minute ago, Stingray~ said:

If your ‘keel’ is not perfectly aligned with your direction when you touch down, you’re gonna be f’d at 50 knots..

tru dat

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23 minutes ago, Stingray~ said:

The skipping stones in some video posted somewhere suggests a rock with a rounded underside has the sweetest skip. As we all know.

Correct and not for stones only, long time ago I have been jumping in water at high speed, if fall from high and get "into" the water you stop immediatly, it's brutal, if you skip you don't feel anything.

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36 minutes ago, phill_nz said:

they will be sailing in the auckland chop

its not always in a constant direction

Also at variable chop length and pitch - wind against tide etc.

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25 minutes ago, Sidecar said:

No doubt in my mind that INEOS UK has been designed as a GEV (ground effect vehicle). Think about it....

These “boats” will be on foils virtually all of the time. And ground effect advantages helps them stay that way, and more stable as well. The hull itself is a “wing” with side fins to guide/redirect airflow.

https://en.wikipedia.org/wiki/Ground-effect_vehicle

https://www.dedoimedo.com/physics/ekranoplans.html

 

502272D2-B0CE-4F9E-85E5-A529BB6CB8E6.jpeg

F64AC301-09C9-4887-8159-14223F20EB20.jpeg

The resemblance is uncanny. Except for the huge low speed wings on the plane, that is.

With air being about 700 x less Dense than water, wouldn't you use the lovely foils with the flaps to control lift and the arms to control x vector to lift the boat, and then concentrate on creating a low drag boat?

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22 minutes ago, Tornado-Cat said:
  44 minutes ago, Stingray~ said:

The skipping stones in some video posted somewhere suggests a rock with a rounded underside has the sweetest skip. As we all know.

 

22 minutes ago, Tornado-Cat said:

Correct and not for stones only, long time ago I have been jumping in water at high speed, if fall from high and get "into" the water you stop immediatly, it's brutal, if you skip you don't feel anything.

You need a brain to register the pain sir. Ya, for sure the designers looked closely at how a rock flies when setting up the parameters of their simulations.

Yeah right

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55 minutes ago, barfy said:

how a rock flies when setting up the parameters of their simulations.

for some reason i first read that as

how a rock flies when setting up the parameters for their ambulance

 

and lets remember a rock has huge mass to volume and if its a good throw spinning at a high rate to keep its directional stability .. when it gets near the end and slowing down it starts slewing to one side

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1 hour ago, barfy said:

The resemblance is uncanny. Except for the huge low speed wings on the plane, that is.

With air being about 700 x less Dense than water, wouldn't you use the lovely foils with the flaps to control lift and the arms to control x vector to lift the boat, and then concentrate on creating a low drag boat?

Exactly. What I had in mind was an airborne low drag/ low lift hull as opposed to an airborne higher drag no lift hull........

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2 hours ago, Sidecar said:

No doubt in my mind that INEOS UK has been designed as a GEV (ground effect vehicle). Think about it....

These “boats” will be on foils virtually all of the time. And ground effect advantages helps them stay that way, and more stable as well. The hull itself is a “wing” with side fins to guide/redirect airflow.

https://en.wikipedia.org/wiki/Ground-effect_vehicle

https://www.dedoimedo.com/physics/ekranoplans.html

 

502272D2-B0CE-4F9E-85E5-A529BB6CB8E6.jpeg

F64AC301-09C9-4887-8159-14223F20EB20.jpeg

The whole ground effect idea I think is a red herring. Foils and especially sail technology is going to win the cup. Not skipping stones. I would be far more concerned about Luna Rossa and their boom-less mainsail than the very uncertain application of ground effect in any meaningful way. I just don't see the differential in air pressure between the top and bottom surface of the hull make that much of a difference considering the effective small area and complex shape of a hull. I am happy to see the challengers go way out on a limb over that idea...

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looks like she is going even more radical

the mastless sail

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4 hours ago, phill_nz said:

for some reason i first read that as

how a rock flies when setting up the parameters for their ambulance

 

and lets remember a rock has huge mass to volume and if its a good throw spinning at a high rate to keep its directional stability .. when it gets near the end and slowing down it starts slewing to one side

Spinning spinning to attain a stability never seen before...The ambulance comes. And sinks like a rock. I think I read that wrong.

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wow .. sounds like you found some really good stuff

what is it ?

 

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4 minutes ago, phill_nz said:

wow .. sounds like you found some really good stuff

what is it ?

 

Well it ain't the world skipping stone open class B)

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19 minutes ago, Varan said:

Didn't somebody mention shrooms upthread?

The magic ones.

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14 hours ago, barfy said:

The resemblance is uncanny. Except for the huge low speed wings on the plane, that is.

With air being about 700 x less Dense than water, wouldn't you use the lovely foils with the flaps to control lift and the arms to control x vector to lift the boat, and then concentrate on creating a low drag boat?

I do wonder what sort of enormous vortex may be generated by the nose and the windward side slab?  There could be some lifting body shizzle going on at 50 knots?

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14 hours ago, phill_nz said:

looks like she is going even more radical

the mastless sail

radical but s+s tops even that!

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So here are my preferences, for what it is worth...

Flipper: beautiful boat, best sailing team, but seems unstable, the crew still has difficulty to tame her, she will need perfect control or will hit the water and/or crash.

Sardine: most beautiful boat by far, not sure that the designer team is the best, the complex sail (like other perhaps) may break during a crash

Orca: I like the flat rounded bottom. The boat is stable, but the stable is not necessarily fast and foils seem big a bit crude on some pictures.

Manta : she gets the prize of ugliness, the boat is interesting though but I am very afraid for the crew in case of pitchpole or any crash, they might be seriously injured or washed out of the boat, it will need some nerves in strong conditions. Foils are very small IMO compared to the others but their design team seems top notch

At the end I would prefer the Orca with good foils.

But how can we pick a boat without knowing the wind limits ?

 

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5 minutes ago, Tornado-Cat said:

So here are my preferences, for what it is worth...

Flipper: beautiful boat, best sailing team, but seems unstable, the crew still has difficulty to tame her, she will need perfect control or will hit the water and/or crash.

Sardine: most beautiful boat by far, not sure that the designer team is the best, the complex sail (like other perhaps) may break during a crash

Orca: I like the flat rounded bottom. The boat is stable, but the stable is not necessarily fast and foils seem big a bit crude on some pictures.

Manta : she gets the prize of ugliness, the boat is interesting though but I am very afraid for the crew in case of pitchpole or any crash, they might be seriously injured or washed out of the boat, it will need some nerves in strong conditions. Foils are very small IMO compared to the others but their design team seems top notch

At the end I would prefer the Orca with good foils.

But how can we pick a boat without knowing the wind limits ?

 

You seem awful scared about the entire show. Take your anxiety meds and start following tennis and failgp, you'll be fine.

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20 minutes ago, Tornado-Cat said:

So here are my preferences, for what it is worth...

Flipper: beautiful boat, best sailing team, but seems unstable, the crew still has difficulty to tame her, she will need perfect control or will hit the water and/or crash.

Sardine: most beautiful boat by far, not sure that the designer team is the best, the complex sail (like other perhaps) may break during a crash

Orca: I like the flat rounded bottom. The boat is stable, but the stable is not necessarily fast and foils seem big a bit crude on some pictures.

Manta : she gets the prize of ugliness, the boat is interesting though but I am very afraid for the crew in case of pitchpole or any crash, they might be seriously injured or washed out of the boat, it will need some nerves in strong conditions. Foils are very small IMO compared to the others but their design team seems top notch

At the end I would prefer the Orca with good foils.

But how can we pick a boat without knowing the wind limits ?

 

The key outtake: "stable is not necessarily fast..."

Want to pic another one, TC?

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35 minutes ago, Liquid said:

Where's the lead in ETNZ foils?

In the wings and lower foil arm.
 

The rule says you can modify 20% of the fool’s mass. One of the current theories is that they have chosen to evenly distribute the weight, at the expense of being able to modify their foils, instead of concentrating the mass in a bulb which means you can modify the wings more freely. 

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11 minutes ago, Ex-yachtie said:

In the wings and lower foil arm.

Doubt there would be any lead in the foils , to much load and stress in those parts.

Cold hard steel more likely.

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There's got to be a min ballast weight in the rule and wouldn't lead foils bend rather quickly?

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2 minutes ago, Priscilla said:

Doubt there would be any lead in the foils , to much load and stress in those parts.

Cold hard steel more likely.

Fair point. 
 

This begs the question then, are the bulbs actually about getting the COG further down the arm? That would make sense in a traditional keel boat where depth equates to righting moment when there is heel, but not so much here. 
 

Having weight further down the arm does however equate the righting moment in the windward arm. 
 

Related question for those less lazy than I am: Does the rule have minimum weight restrictions for the arm? Could ETNZ simply have opted to put less weight in?

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Just now, Ex-yachtie said:

Fair point. 
 

This begs the question then, are the bulbs actually about getting the COG further down the arm? That would make sense in a traditional keel boat where depth equates to righting moment when there is heel, but not so much here. 
 

Having weight further down the arm does however equate the righting moment in the windward arm. 
 

Related question for those less lazy than I am: Does the rule have minimum weight restrictions for the arm? Could ETNZ simply have opted to put less weight in?

Could the torpedo weight have the most effect as outboard weight on the windward foil arm?

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5 minutes ago, Ex-yachtie said:

Fair point. 
 

This begs the question then, are the bulbs actually about getting the COG further down the arm? That would make sense in a traditional keel boat where depth equates to righting moment when there is heel, but not so much here. 
 

Having weight further down the arm does however equate the righting moment in the windward arm. 
 

Related question for those less lazy than I am: Does the rule have minimum weight restrictions for the arm? Could ETNZ simply have opted to put less weight in?

 

The arms are one-design I think,

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8 minutes ago, Sailbydate said:

Could the torpedo weight have the most effect as outboard weight on the windward foil arm?

I think that’s what I’m saying in my third (of four) paragraph. 

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5 minutes ago, arneelof said:

 

The arms are one-design I think,

Sorry, I should have been clearer. I meant the lower part of the arm, below the one design bit. 

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My thinking is ballasted foils are trainers where Te Aihe has gone straight to steel without torpedoes and the simulator and now reality shows up that immersed foil lift forces are the go to area of interest rather than the fulcrum balancing weight of the windward raised foil.

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So, we can agree the torpedo set have arrived at their torpedo foil solutions, because of their experience with their test boats.

But what if this lump of lead has nothing at all to do with faster foils and is simply a solution to improve RM through outboard weight?

Is the penalty of that additional drag going to be expensive in terms of speed?

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7 minutes ago, Sailbydate said:

So, we can agree the torpedo set have arrived at their torpedo foil solutions, because of their experience with their test boats.

But what if this lump of lead has nothing at all to do with faster foils and is simply a solution to improve RM through outboard weight?

Is the penalty of that additional drag going to be expensive in terms of speed?

The weight of the foil systems will be very similar. It is just a difference of distributing that weight for other design reasons. So no real difference in the RM. Just more drag

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1 minute ago, uflux said:

The weight of the foil systems will be very similar. It is just way of distributing that weight for other design reasons. So no real difference in the RM. Just more drag

So, uflux are you saying that the torpedoes are likely faster foils (since there's no RM gain) - otherwise why bother?

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Just now, Sailbydate said:

So, uflux are you saying that the torpedoes are likely faster foils (since there's no RM gain) - otherwise why bother?

No, the torpedo bulb allows the modification of the wings more freely according to the rules. So there is a balance of design freedom verse potential drag penalty of the bulb. ETNZ current doesn't feel they need that. So potentially doesn't have that drag penalty. The RM will be very similar as the weight is distributed in the foil. But then there is all the other foil parameters around twist, flex, stiffness, foil shapes, tip vortices which all have a huge effect that people seem to ignore. ETNZ winning foils in Bermuda were a lot more than simply their length or shape. I am not at all worried about their ability to have the best foils in the fleet by the time of AC.

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On 10/4/2019 at 7:39 AM, Mozzy Sails said:

...Interesting little fences and strips on the Lunna Rossa and Britannia foils. 

My guess is they are hinges on the bottom of the Britannia foils.  Moving the hinge axis down means the flap moves aft as it is deflected, like a Fowler flap.  This adds area and may open up a slot for high lift at low speed to aid in taking off under marginal conditions.

To be effective as fences, they'd need to be at the leading edge and on the upper surface.  

The Luna Rossa fairings are wider than needed for a hinge, plus there's only one on each side, so that's why I suspect they have actuators in them.  Luna Rossa does look to have fences inboard of the bend at the tip.

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56 minutes ago, Basiliscus said:

My guess is they are hinges on the bottom of the Britannia foils.  Moving the hinge axis down means the flap moves aft as it is deflected, like a Fowler flap.  This adds area and may open up a slot for high lift at low speed to aid in taking off under marginal conditions.

To be effective as fences, they'd need to be at the leading edge and on the upper surface.  

The Luna Rossa fairings are wider than needed for a hinge, plus there's only one on each side, so that's why I suspect they have actuators in them.  Luna Rossa does look to have fences inboard of the bend at the tip.

Yeah, it's going to be interesting how that evolves as anything protruding is going to contribute to potential cavitation issues at high speeds. I think the top surface fences on LR suggest a design issue of not being able to manage the spanwise flow. Maybe the last minute redesign with a bulb? A very 1950s solution. 

https://en.m.wikipedia.org/wiki/Wing_fence

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1 hour ago, Basiliscus said:

My guess is they are hinges on the bottom of the Britannia foils.  Moving the hinge axis down means the flap moves aft as it is deflected, like a Fowler flap.  This adds area and may open up a slot for high lift at low speed to aid in taking off under marginal conditions.

To be effective as fences, they'd need to be at the leading edge and on the upper surface.  

The Luna Rossa fairings are wider than needed for a hinge, plus there's only one on each side, so that's why I suspect they have actuators in them.  Luna Rossa does look to have fences inboard of the bend at the tip.

Ooohh, clever. Do the rules allow for increased foil area with flap deflection/extension?

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12 minutes ago, amc said:

Ooohh, clever. Do the rules allow for increased foil area with flap deflection/extension?

"At any cross-section and all rotation angles, when projected on to the foil wing projection plane, the length
of a foil flap must not be greater than 50% of the chord length. Hinges or other parts of a component which
occur at occasional cross-sections for connection purposes can be excluded from the projected lengths."

Capture.PNG

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4 hours ago, Sailbydate said:

The key outtake: "stable is not necessarily fast..."

Want to pic another one, TC?

Sophisticated is not necessarily fast and may break.

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2 hours ago, uflux said:

No, the torpedo bulb allows the modification of the wings more freely according to the rules. So there is a balance of design freedom verse potential drag penalty of the bulb. ETNZ current doesn't feel they need that. So potentially doesn't have that drag penalty. The RM will be very similar as the weight is distributed in the foil. But then there is all the other foil parameters around twist, flex, stiffness, foil shapes, tip vortices which all have a huge effect that people seem to ignore. ETNZ winning foils in Bermuda were a lot more than simply their length or shape. I am not at all worried about their ability to have the best foils in the fleet by the time of AC.

image.png.30413912d7f2601cfea997d70d4b79ad.png

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On 10/4/2019 at 9:46 PM, Sugarscoop said:

Which hull "by its self" would perform best in a wind tunnel. Im picking AM

there's no point considering the hull by its self... there's no point speculating about what will and won't perform best in a wind tunnel from pictures... i guess there's no point saying this either. carry on

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13 minutes ago, Tornado-Cat said:

"At any cross-section and all rotation angles, when projected on to the foil wing projection plane, the length
of a foil flap must not be greater than 50% of the chord length. Hinges or other parts of a component which
occur at occasional cross-sections for connection purposes can be excluded from the projected lengths."

Capture.PNG

So that would seem to be a yes then. 

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5 minutes ago, buckdouger said:

image.png.30413912d7f2601cfea997d70d4b79ad.png

Sweet.. thanks for confirming my point

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