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Gitana Maxi 17

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Question: Could it be that too much load was placed on the Ama foils?  Unlike a CAT, aren't the ama foils more concerned with RM than lifting the whole boat out of the water.  Shouldn't the center foil do most of the lifting?  Maybe the center foil lift factor was under calculated placing too much of the boats weight on the outer foils.  

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Actually, the center foil only does a lot of lifting in relatively light winds to help keep the main hull flying. In stronger winds the center foil would be used for both lift and downforce. As the boat starts to fly some weight will be on the main foil but will shift to the lee ama foil which will carry the weight of the boat + any downforce from the center foil.

Max RM is created when the ama foil is lifting the whole boat---the distance from the CG of the boat to the center of lift of the lee ama foil is the righting arm-that distance multiplied by the weight of the boat is righting moment. The center foil adds to the max RM with downforce and subtracts from it with any lift.

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I've posted this in the TJV thread already, but it might be good to have it here as well...

The French version of the article on the TJV site (https://www.transatjacquesvabre.org/fr/actualites/sillages/477/sodebo-ultim-maxi-edmond-de-rothschild-le-grand-debriefing) has a longer quote from Seb Josse in which he says: "It is a composite problem, we have to look into it in more detail, I don't know what caused it. The foils are no longer in their original state, they are more flexible than they should be."

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6 hours ago, surlepont said:

I've posted this in the TJV thread already, but it might be good to have it here as well...

The French version of the article on the TJV site (https://www.transatjacquesvabre.org/fr/actualites/sillages/477/sodebo-ultim-maxi-edmond-de-rothschild-le-grand-debriefing) has a longer quote from Seb Josse in which he says: "It is a composite problem, we have to look into it in more detail, I don't know what caused it. The foils are no longer in their original state, they are more flexible than they should be."

Wow.... sounds like that means the foils themselves, and not the mechanical/systems/attachments.  If true, I'm guessing that means there is going to be some considerable time with the boat in the shop..... possibly a need for entirely new foils?

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Sounds like new ones for the most part. Floppy foils means that the laminate broke down, delamination and broken strands. 
Question is if their construction uses a metal knee and if the damage is confined to one side of it.

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Difficult to judge from the pictures, but compared to Banque pop IX ,or even the last AC foils, Gitana foils look really "skinny".

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Just saying that the foil are delaminating.

And because of the flex resulting, it w1s slowing them by producing negative foil effect and pulling them down

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10 minutes ago, GauchoGreg said:

For our French-speakers, anything of note in the video, below:

https://www.youtube.com/user/gitanateam

Not really anything new, he says that the foils got delaminated, and got too soft, so that they even had an inverse effect(getting the boat down) , so that they need to go back to the drawing board with the design office to get them up to what they are intended for, 40 days around the world. 

Otherwise they were pleased with the boat seaworthyness and ergonomy. 

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I guess Team Gitana doesn't mind showing their faulty stuff.... before they were a bit cagey about letting anyone see these foils.  That is a big-ass-foil.

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So this is on the trailing edge ?

I would have guess the oposite

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21 minutes ago, popo said:

So this is on the trailing edge ?

I would have guess the oposite

I was thinking the same thing.... but maybe more flex there, delaminating the skin of the thinner trailing edge?

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French translation from Dolfiman on boatdesign.  Discussion of the course error that cost Gitana 124 miles. Without this error they still could have won:

From Dolfiman in the Transat thread:
If Gitana speed potential is not technically affected, they still have a chance, they already show at the beginning of the race that they are able to go faster than Sodebo in reaching conditions. Their delay in time is only 30 mn. On the other hand Sodebo is a very sharp machine and currently easier to lead at 100% than new Gitana still in the learning curve as confessed Seb Josse on their site. He also confessed their wrong route option 2 days ago (it was not a tactical move as I presumed optimistically), in french on their site :
"Thomas and Jean-Luc played a nice weather option that explains today that they are leading the race. After the passage of the Azores we had the choice between jibing several times or going under J0 (big gennaker). Given our position at that time, we opted for gybing and navigation under J1 (genoa) which was to allow us to gain in longitudinal. Sodebo made the opposite choice by shifting in the West to slip. Our choice did not pay, far from it. Not only the state of the sea in the night from Tuesday to Wednesday did not allow us to exploit as expected our choice of sail and our meeting with a grain without wind pushed the nail. In the end, it was Thomas and Jean-Luc who pulled the right edge and in view of the weather conditions that presented themselves in front of our bows we had last night to jibe at 90 ° of the road to get away from the African coast and areas of light winds in our south. On the way out of this resetting, the addition was salty: from a 64-mile credit at 21h, Gitana 17 conceded 60 miles at sunrise. "t's always hard as a decision but the evening files were very clear. Sometimes you have to know how to lose a little to not completely mortgage the next events" .

 

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That's not a "course error". That was at the time choosing the option that made the most sense for them.

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20 hours ago, ctutmark said:

from the UltimBoat FB page 

Image may contain: 2 people, child and outdoor

Is that a honeycomb core........ you have Got to be shitting me...

More carbon in my kitesurfing mast

 

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22 hours ago, Doug Lord said:

French translation from Dolfiman on boatdesign.  Discussion of the course error that cost Gitana 124 miles. Without this error they still could have won:

From Dolfiman in the Transat thread:
If Gitana speed potential is not technically affected, they still have a chance, they already show at the beginning of the race that they are able to go faster than Sodebo in reaching conditions. Their delay in time is only 30 mn. On the other hand Sodebo is a very sharp machine and currently easier to lead at 100% than new Gitana still in the learning curve as confessed Seb Josse on their site. He also confessed their wrong route option 2 days ago (it was not a tactical move as I presumed optimistically), in french on their site :
"Thomas and Jean-Luc played a nice weather option that explains today that they are leading the race. After the passage of the Azores we had the choice between jibing several times or going under J0 (big gennaker). Given our position at that time, we opted for gybing and navigation under J1 (genoa) which was to allow us to gain in longitudinal. Sodebo made the opposite choice by shifting in the West to slip. Our choice did not pay, far from it. Not only the state of the sea in the night from Tuesday to Wednesday did not allow us to exploit as expected our choice of sail and our meeting with a grain without wind pushed the nail. In the end, it was Thomas and Jean-Luc who pulled the right edge and in view of the weather conditions that presented themselves in front of our bows we had last night to jibe at 90 ° of the road to get away from the African coast and areas of light winds in our south. On the way out of this resetting, the addition was salty: from a 64-mile credit at 21h, Gitana 17 conceded 60 miles at sunrise. "t's always hard as a decision but the evening files were very clear. Sometimes you have to know how to lose a little to not completely mortgage the next events" .

 

Again, it is highly likely Gitana could have won despite their foil and engine problems if they hadn't made this mistake. The distance behind at Sodebos finish was somewhere around 30-40NM as best I can tell.

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From the Gitana site:

Thomas Rouxel: Ah! It was my first Transat Jacques Vabre and I wouldn't have said no to a little victory! But here we are with this second place and that's no small feat. We made a strategic error at the Azores, which cost dearly and I think it was one of the key points in the race. Added to that, we had foil issues, which no longer enabled us to make a difference in terms of speed. Furthermore, we were up against two mighty candidates.

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Ok Dougie, we've got the point. Stop posting the same thing on every thread. The history will tell Sodebo won, Gitana came in second, you will have to live with that. No one of the gitana crew is saying they would have won, you are the one implying that. Gitana probably will win TJV some day, but not today, no matter how much you post about it. If, If, If... If my sister had balls would be my brother.

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4 hours ago, Chasm said:

Some post race analysis by the skippers. [EN version]

Thanks.Enjoyed that.      Did he say  2 or 3 hundred litres is insignificant? Seems like a lot.

Quote

d'une société un truc c'est qu'on 02:42 commence à regarder si on avait pas 02:44 d'eau dans les flotteurs au confort 02:45 auquel est un petit peu 200 300 litres 02:47 mais c'était pas significatif

 

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I think he more meant that 200 or 300 litres wasn't the explanation for feeling sluggish and they then realised they had a second foil issue.

But I agree, 300 kilos is plenty of weight.

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Not enough water to explain all of the performance loss, a look at the foil and it was also damaged.

I wonder when they decided to include shots of the damage, before or after seeing one of them on FB.
Without watching the video yet again it seems that we have only the port foil in it. So some secrecy is preserved. :)

Anyway, good that they made the start of the TJV and tried the boat in a race.

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On 11/15/2017 at 6:27 AM, popo said:

So this is on the trailing edge ?

I would have guess the oposite

Whether Gitana will ever share their findings is both unlikely and moot.

Remember that the large offshore multihull teams, whilst being competitive, are operating in a small collaborative world of designers, fabricators and personnel, so those who need to know will, and florida modelmakers won't.....

What the picture does reveal is that the damage did not propagate from impact damage on the leading edge.

If you want to speculate then it can be seen that the delamination has occured in the zone of greatest foil curvature.

This would be suggestive of where turbulance, and possible cavitation would most likely propagate. The smallest flaw in the structure or even surface finish would emanate and spread from there - up, down and forward.

Recall how Oracle's AC72 rudders needed repainting and refairing after each and every day leading to the fillet and intersection work by Bieker - and that was after a few hours of use. Gitana's failure was after nearly a week of angry use..... Think also of the foil flutter, as witnessed in even monohulls such as imoca, or at least the forces trying trying to force flutter - which again would be greatest at the thin trailing edges and propagating from there. The magnitude of forces is we know very high and the foil is most suseptible at its thinnest part, which makes the damage spreading from the trailing edge more likely, even if slightly counterintuitative. 

The structural makeup is interesting - remember that the honeycomb core that is exposed, is unklikely to be uniform through the whole section. A tubular spar like structure is more likely to be found where the foil chord is thickest. 

Are there any pictures of the reverse side of the foil where we have seen some pictures of some very aggresively shaped chord sections?

 

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 Do you think cavitation would be enough to rip off the skin like that or would it just leave it on and flappy?

Could a small strike on the leading edge be enough to crack the skin and start the ball rolling.

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Cavitation can eat bronze props very quickly. It would have no trouble carving up a carbon structure .

My guess isn't cavitation (because the trailing edge of the foil won't have the biggest pressure differentials).

I guess structural failure due to the foil just overloading. I don't understand what I am seeing with a core but it doesn't look like honeycomb.

Not leading edge damage - because it was both foils in same area 

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Looks like a similar foam as coremat - which if so, seems strange to me because it is not a strong material; also quite heavy. But don't know the material in photograph, just looking. The carbon laminates in the trailing sections, although broken and gone, looks also minimal - and the gash/rip entering the mid section area doesn't look substantial either. Would have thought these hard working foils would have been solid carbon?

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30 minutes ago, Groucho Marx said:

Looks like a similar foam as coremat - which if so, seems strange to me because it is not a strong material; also quite heavy. But don't know the material in photograph, just looking. The carbon laminates in the trailing sections, although broken and gone, looks also minimal - and the gash/rip entering the mid section area doesn't look substantial either. Would have thought these hard working foils would have been solid carbon?

Yes would also have thought that the foils were solid carbon, especially in the part we see, maybe not the "vertical" shaft, anybody knows if it is the case for the AC foils ?

For these not solid carbon, I wonder if the purpose was to save weight or for some mechanical characteristics (flexibility or something).

Saving weight on such critical pieces seems a bit strange.

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Admittedly totally ignorant to the engineering/physics of this.... but I was thinking the same, solid carbon would seem the least likely to end up with structural failure from long-term flexing.  Then, thinking of the abuse from cavitation, is there any way to have a skin of titanium, ceramic, ??? over the carbon (not sure the properties of carbon for dealing with the impact of cavitation)?  Given the apparent performance gain from the foiling as seen in the first day or so against Sodebo, I think upping the investment in the foils to "whatever it costs" is more warranted than ever, now supported by the early performance off-shore.

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3 hours ago, GauchoGreg said:

Admittedly totally ignorant to the engineering/physics of this.... but I was thinking the same, solid carbon would seem the least likely to end up with structural failure from long-term flexing.  Then, thinking of the abuse from cavitation, is there any way to have a skin of titanium, ceramic, ??? over the carbon (not sure the properties of carbon for dealing with the impact of cavitation)?  Given the apparent performance gain from the foiling as seen in the first day or so against Sodebo, I think upping the investment in the foils to "whatever it costs" is more warranted than ever, now supported by the early performance off-shore.

Also far from my area of expertise but I do recall reading that especially in this area of the foils, when very large, it is best to not go all carbon due to issue with having correct orientation of the fibers.  Doubt I can easily find it but it was a technical article speculating about AC and maxi multi foils.  Much of it over my head but I do recall the comments about not wanting all carbon there as the foil and boat got very large.

God save me from the Lord for I have typed the word foil and surely man of many strange capitalizations, and colored letters, and yet one redundant notion forever applied to everyone else's good  work... will come to haunt this space.  God forgive me and have mercy on my foiless soul.  :lol:

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On 11/15/2017 at 2:42 PM, Kenny Dumas said:

I guess that would be the lowest pressure area, so cavitation is an interesting possibility.  

Hobby horsing on the foil, whole leading edge was much stronger so the back half failed.

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I built a pair of rudders for a fast motor cat that were overbalanced. After many arguements over the rudder post placement and lead for balance it was found during seatrials that if one turned to far or fast at speed the overbalance would overcome the pressure poppet safety valve in the hydraulic steering and the rudders would go to full stop and cavitate/stall like you wouldn't believe. The rudders were heavily glass/epoxied over foiled plywood cores and the collapse of the cavitation bubble ate through the glass and into the core over the aft half of the rudder much like you see here. Looks like similar damage to me.

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The strange thing is that it is cored. Every foiler I've seen over the past 3+ years has gone straight to monolithic construction thanks to the hard lessons from the mothies and the rest of the foilers.

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The argument that you cannot align the carbon laminates to counter loads just doesn't hold water - sorry, bad pun.

Looking at the G17 photograph (how secretive was the photographer and more thanks to you - otherwise we would know nothing) - the foil laminates look very DoUgLoRd amateurish - were the Rothschilds running out of cash?

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It’s not honeycomb it’s pinholed foam - ie foam intended for use under vacuum to prevent voids. The black spots are where the (black poss spa bond or some such) core bond adhesive gets into the pinholes which show that the whole vac bonding is working. The foam is probably the very dense stuff that has similar mech properties to oak. 

I dare say that structurally this is fine assuming there is a spar and like what somebody said, either damage or cavitation, which will eat bronze propellers. 

Think 40 plus kts alone won’t cause cavitation, but 40 plus kts plus enough negative pressure to “boil” the water, the subsequent collapse of the bubbles being what erodes the surface of the foil / prop.

in propeller world, among other things you might look to reduce that pressure by increasing blade area, diameter, reducing pitch increasing revs or some

Combination therof.

Did any ac boats get this sort of damage? 

I suspect that the more offshore scenario of very variable loads with boat motion combined with going in and out of the waves in a transient manner may have precipitated this, and it probably would not be straightforward to just up the area. 

Making it monolithic would not help if it is cavitation erosion, you are still basically taking an watery angle grinder to the surface. Harder substance ie metal may reduce the rate of erosion but then you are into something heavier and bendier. 

Dan

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Normal construction for foils of this size. One cannot compare/scale up from a moth. The foil will most likely have a main structural spar with foam cored leading and trailing edges. There are a lot of constraints when designing and building these boats both with time and budget so it is not that surprising to have a failure when pushing the limits as they are.

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Continuous or sectional spar? I would have thought sectionals.

The cavitation makes sense to this uninformed uneducated watcher simply because it apparently happened  so quickly and on both foils. But... I wouldn't have thought they would be running the foils at speeds or settings that would produce loads different than they saw on the work up?! So why cavitation during the race and not the work up?  If similar loading and settings doesn't that suggest something more gradual and then catastrophic than cavitation suggests?

All speculation anyway and doubt they will ever say but interesting to follow...

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2 hours ago, Daniel Holman said:

It’s not honeycomb it’s pinholed foam - ie foam intended for use under vacuum to prevent voids. The black spots are where the (black poss spa bond or some such) core bond adhesive gets into the pinholes which show that the whole vac bonding is working. The foam is probably the very dense stuff that has similar mech properties to oak. 

I dare say that structurally this is fine assuming there is a spar and like what somebody said, either damage or cavitation, which will eat bronze propellers. 

Think 40 plus kts alone won’t cause cavitation, but 40 plus kts plus enough negative pressure to “boil” the water, the subsequent collapse of the bubbles being what erodes the surface of the foil / prop.

in propeller world, among other things you might look to reduce that pressure by increasing blade area, diameter, reducing pitch increasing revs or some

Combination therof.

Did any ac boats get this sort of damage? 

I suspect that the more offshore scenario of very variable loads with boat motion combined with going in and out of the waves in a transient manner may have precipitated this, and it probably would not be straightforward to just up the area. 

Making it monolithic would not help if it is cavitation erosion, you are still basically taking an watery angle grinder to the surface. Harder substance ie metal may reduce the rate of erosion but then you are into something heavier and bendier. 

Dan

Very good explanation (imho). 

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I would put my money on stress risers due to the (what seems to be) instant transition from the load bearing beam to the thin skins on the trailing part of the foil. You're bound to have some flex in that area, and a transition like that seems like a breakage waiting to happen....

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So have I Macif'd something or or is Gitane'd now.? Gitana has Verdier stamped on it and needs to be driven by FG for maximum speed. 881 miles but I think FG could get 900 within 2 months. Gitana has all the potential in the right hands.

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18 hours ago, MR.CLEAN said:

The strange thing is that it is cored. Every foiler I've seen over the past 3+ years has gone straight to monolithic construction thanks to the hard lessons from the mothies and the rest of the foilers.

This is a Verdier boat but you guys are guessing circumstances. Last time I checked Verdier were King? Plenty of factors that come into play surely there needs to be some more digging? Just saying..

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4 hours ago, Daniel Holman said:

Did any ac boats get this sort of damage? 

Dalton said they checked the foils every day with ultrasound cause they were on the limit

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7 hours ago, Daniel Holman said:

....

I suspect that the more offshore scenario of very variable loads with boat motion combined with going in and out of the waves in a transient manner may have precipitated this, and it probably would not be straightforward to just up the area. 

Making it monolithic would not help if it is cavitation erosion, you are still basically taking an watery angle grinder to the surface. Harder substance ie metal may reduce the rate of erosion but then you are into something heavier and bendier. 

Dan

Again, coming from an ignorant person (myself), but this seems like a reasonable theory (the variability and extreme loads and vacuums created by going through heavy seas resulting in far more intense cavitation than simply flying along on flat water).

Again, from an ignorant person (myself), but would it be possible to wrap a carbon (and foam, if it makes the most sense) foil with an extremely resistant material (to cavitation), rather than whatever pigmented laminate/gelcoat/whatever they used?  I'm no metallurgist (and there very likely is something better, just thinking of something light and extremely durable), but could you use titanium as a shell (I know it is bendy, but who cares as a shell)?  I know a titanium company would like that order.

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6 hours ago, CRSNZ said:

Normal construction for foils of this size. One cannot compare/scale up from a moth. The foil will most likely have a main structural spar with foam cored leading and trailing edges. There are a lot of constraints when designing and building these boats both with time and budget so it is not that surprising to have a failure when pushing the limits as they are.

Pretty sure Boss foils are monolithic.  maybe it doesn't scale up, maybe it does.  Point is that AC boats, IMOCA boats, GC32, G4 all have gone to monolithic despite most starting with cored because damage.

Would think monolithic will hold up longer when cavitation or torsional issues start tearing up trailing edge, especially useful for an ocean vs. lake course.  see cf. ETNZ 50.

 

 

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29 minutes ago, GauchoGreg said:

could you use titanium as a shell (I know it is bendy, but who cares as a shell

if you find a metal that can flex as much as a carbon foil yet be resistant to cavitation (which tears up stainless props like concrete), let us know please!

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4 hours ago, terrafirma said:

This is a Verdier boat but you guys are guessing circumstances. Last time I checked Verdier were King? 

This is the first and only maxi multihull that Verdier have done without VPLP, and there's quite a bit of bad blood over it, and keep in mind that the Verdier foils that won the America's Cup barely survived to the last race.

One would fully expect some teething issues, the question will be how quickly does the design and build team respond and how well does the new setup do?

 

 

 

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Clean,

     I am under the impression that titanium will flex far more without breaking that a comparable carbon fiber component. Carbon is stiff and somewhat brittle and when it fails it is usually with no warning. Certain grades of Titanium are used for springs, ever see the sunglass frames that you can tie in a knot without permanent deformation or breakage?

 

 

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54 minutes ago, GauchoGreg said:

but would it be possible to wrap a carbon (and foam, if it makes the most sense) foil with an extremely resistant material (to cavitation), rather than whatever pigmented laminate/gelcoat/whatever they used?  I'm no metallurgist (and there very likely is something better, just thinking of something light and extremely durable), but could you use titanium as a shell (I know it is bendy, but who cares as a shell)?

The Terminator foil.

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6 hours ago, CRSNZ said:

Normal construction for foils of this size. One cannot compare/scale up from a moth. The foil will most likely have a main structural spar with foam cored leading and trailing edges. There are a lot of constraints when designing and building these boats both with time and budget so it is not that surprising to have a failure when pushing the limits as they are.

I find this image super interesting, thanks for posting! Yeah that foam looks like it's just a fairing behind the main spar, i would be surprised if it would make much difference whether that area was monolithic or not due to how thin it is relative to the rest of the section. The principle behind the structure seems to make sense, and im sure the laminate is as designed. I imagine that the loads in big waves could be fairly hard to predict and would be right up there when the hull crashes down and the foil slaps on the water at like 30 degrees AOA.  Seb's report that the lift was gone, even negative lift making the boat feel heavy.. suggests in my mind that the spar is de-laminated and the tip section of the foil is twisting off under load. And all that damage could just be the skin shitting itself as the spar flaps around under water.

I guess when you design these things, you're always trying to make them thinner for drag but thicker for structure - for a given structural system. So hard to find that ideal balance. I'm sure the BP design team are looking at this carefully also, I wonder if this suggests that everyone's assumptions about max loads need to be updated?

 

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36 minutes ago, MR.CLEAN said:

One would fully expect some teething issues, the question will be how quickly does the design and build team respond and how well does the new setup do?

 

They have gone to a fair amount of trouble to build this boat, I'm sure they are on it!

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1 hour ago, MR.CLEAN said:

if you find a metal that can flex as much as a carbon foil yet be resistant to cavitation (which tears up stainless props like concrete), let us know please!

As I said, I'm not a metallurgist, but was under the impression that titanium is far more flexy than other metals (and I thought more flexy than carbon, too, but again, not my forte) while retaining incredible lightness and toughness (I know it can be great material for places where you want a light yet dampening material, like with handlebars on mountain bikes, where carbon may be stiffer, but may not be as desirable for frames when you want them to be stiff/unflexy).  My question was a genuine question, not a suggestion they do something as if I'm an authority.  That's why I was thinking MAYBE it could work as a shell/veneer over the carbon, just to implement a barrier to slow down the impact of cavitation.  I would expect it very difficult to completely avoid cavitation due to the constant changes of orientation to the water flow as the boat is impacted by waves.

 

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You can fool someone all the time, you can fool everyone for some time, but you cannot fool everyone all the time. Guess that foling in a long distance race is the same.They can run simulations, tests, whatever , but it will always be a compromise solution. IMHO forces involved are unpredictable. Surely they 'll come around the issue, but at what cost? Heavier? Less aerodynamic profile? More drag? Faster on optimal conditions? Slower in normal ? Will it pay in the long run?

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Not the first bit of a Verdier boat to have issues and the Hugo Boss foil that broke first time out testing was not monolithic but had the multiple hollows, and then HB had the cheek to sue the foil builders.  And that after all the hull failures on the new Verdier boats.  Does seem he has an issue with his composite engineering.   Big issue with all these foils are the transient loads which can peak at way over steady state stalled conditions and are extremely hard to predict.  Then the flex on these things eventually causes micro cracking in the resin and when that stops keeping the fibres aligned then all bets are off.  Lots of possible reasons for failure  but trying to pin down the exact sequence and reasons for failure not easy at all.  And whatever is learnt won't get out and thats for sure!  Funny how all the Vendee foil failures were blamed on impacts:)

 

 

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That white stuff ,It's not foam  its coremat for bulking out the laminates. Just need to get the fabric  laminate mixture  right ,she then be good to go. Saying it's right on a drawing board is only one part of it . Was impact testing carried out? I doubt it. From build to water  with a prototype  breakages are going to happen. Well done to all competitors and all involved  and a big thank you to the French on leading the world stage of yachting.

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I find it hard to believe any explanation that cavitation is responsible for destroying the foil.

 

If that were the case, there would be evidence of that occurring elsewhere all ready, like mothe, kitefoilers, AC72, AC40, bla bla bla

 

 

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I think cavitation erosion is pretty well documented in the 40-50 knot range. I dont think Moths or kitefoilers ever really see those speeds?, but certainly on a boat like this it would be a consideration. Would be cool to see pics of what the result looks like - ie from the AC - expect to see some kind of patterned pitting on the surface similar to this? 

Figure-49-Cavitation-erosion-is-visualiz

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Perhaps it's not the only cause, but it's very meaningful where the damage is worse (trailing edge and bend). Perhaps it is not happening in the other boats you mentioned cause circumstances are different, and they don't add up. Guess we will never know for sure. One thing that always drew my atention is the noise the foils make. Noise is one of cavitation syntoms (that's what I've heard, not that I'm a specialist)

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8 hours ago, GBH said:

Not the first bit of a Verdier boat to have issues and the Hugo Boss foil that broke first time out testing was not monolithic but had the multiple hollows, and then HB had the cheek to sue the foil builders.  And that after all the hull failures on the new Verdier boats.  Does seem he has an issue with his composite engineering.   Big issue with all these foils are the transient loads which can peak at way over steady state stalled conditions and are extremely hard to predict.  Then the flex on these things eventually causes micro cracking in the resin and when that stops keeping the fibres aligned then all bets are off.  Lots of possible reasons for failure  but trying to pin down the exact sequence and reasons for failure not easy at all.  And whatever is learnt won't get out and thats for sure!  Funny how all the Vendee foil failures were blamed on impacts:)

 

 

Exactly which boats and which failures are you referring to?

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IIRC only two boats had foil probleme during the VG

Boss and gitana

Boss said to hit something but gitana had the weather foil casing (and not the foil) damaged by a wave

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41 minutes ago, Doug Lord said:

Exactly which boats and which failures are you referring to?

TJV 2015  and all of them with major hull problems.  Short memories?

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8 hours ago, CARBONINIT said:

That white stuff ,It's not foam  its coremat for bulking out the laminates. Just need to get the fabric  laminate mixture  right ,she then be good to go. Saying it's right on a drawing board is only one part of it . Was impact testing carried out? I doubt it. From build to water  with a prototype  breakages are going to happen. Well done to all competitors and all involved  and a big thank you to the French on leading the world stage of yachting.

Struggling to understand why anyone would use coremat? It’s about the poorest core material available and generally only used in polyester lay ups. 

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No way anyone would use Coremat in those foils. That stuff soaks up so much resin and is a cheap bulker that would be totally  inappropriate used with that much carbon fiber on such a high profile project. 

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3 hours ago, Rasputin22 said:

No way anyone would use Coremat in those foils. That stuff soaks up so much resin and is a cheap bulker that would be totally  inappropriate used with that much carbon fiber on such a high profile project. 

Exactly my point. 

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The GE90 engine (on the Boeing 777) has had a carbon fibre fan blade with a titanium leading edge since around 2003, so clearly matching the flexibility between the two materials is possible.  However, I seem to remember that getting the bonding right in production was the big difficulty.  Suspect that it would be even more difficult over the full surface of a foil (and GE have $ millions to spend on R&D)

Interesting to see that a European research project Amedeo is looking at trailing edge inserts as well as leading edge (the leading edge is for bird strike tolerance) - I wonder whether the titanium on the trailing edge is to allow the trailing edge to be made thinner but stiff enough?

Clearly fan blades don't have cavitation issues - flutter is the big structural issue (along with bird strike) - so don't know if titanium would solve the Gitana issue (if it is cavitation - I could believe that it was flutter that caused the issues.  I don't know enough about cavitation to comment either way)

VKI_CC_CompFan_text2.jpg

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Fan blades have erosion problems from rain and hail, hence the need for either ceramic coatings or metallic leading edges to the blades. Trailing edge is for stiffness on a thin section.

Gitana foil though you can see clearly the crumple area, so one thing to figure is if the delam/peel in the aft section was responsible for that, or the consequence of something else.  From the lack of any damage to the leading edge then impact is probably ruled out, so more likely to be combination of load factors both torsional and direct bend and drag loadings that has found out the structural weakness there.

Superficially, would reckon the aft upper skin started to fail just around and out from the elbow, then the water would rip that off and do the rest of the visible damage.

White core I would reckon is simply a well pierced machined hd foam - that allows resin migration under vac and forms resin columns in the foam between the skins.   Whatever, will be an expensive fix.

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2 hours ago, GBH said:

Fan blades have erosion problems from rain and hail, hence the need for either ceramic coatings or metallic leading edges to the blades. Trailing edge is for stiffness on a thin section.

Gitana foil though you can see clearly the crumple area, so one thing to figure is if the delam/peel in the aft section was responsible for that, or the consequence of something else.  From the lack of any damage to the leading edge then impact is probably ruled out, so more likely to be combination of load factors both torsional and direct bend and drag loadings that has found out the structural weakness there.

Superficially, would reckon the aft upper skin started to fail just around and out from the elbow, then the water would rip that off and do the rest of the visible damage.

White core I would reckon is simply a well pierced machined hd foam - that allows resin migration under vac and forms resin columns in the foam between the skins.   Whatever, will be an expensive fix.

Just make it out of solid carbon, like HB and commanche.

 

Then it won't delaminate.... easy.

Kite foilers up around the 40 kt mark.... however they are mostly solid carbon, and definatly no foam core - hence no delamination

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The AC50 foils on TNZ were solid carbon and were delaminating if the article I read is to be believed. Just because something is solid doesn't mean its capable of taking the loads. It is still possible to draw an airfoil section that is too thin to actually build. In this case, I suspect they underpredicted the forces on the foil in torsion and probably net pressure force. I say this as they clearly got the main spar ahead of the primary delamination spot correct, otherwise there is a good chance the foil would have snapped.

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3 hours ago, dachopper said:

Just make it out of solid carbon, like HB and commanche.

 

Then it won't delaminate.... easy.

Kite foilers up around the 40 kt mark.... however they are mostly solid carbon, and definatly no foam core - hence no delamination

HB and Comanche lack the Gitana speeds. Kite foilers don't manage forces involved in Gitana. IMHO not comparable.

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On 11/19/2017 at 10:08 AM, popo said:

IIRC only two boats had foil probleme during the VG

Boss and gitana

Boss said to hit something but gitana had the weather foil casing (and not the foil) damaged by a wave

IIRC the Gitana failure was force down on the foil generated by a large wave, not normal lifting force.  Could be a contributory issue in this case also?  Gotta be some huge "wrong way" forces on these foils in big seas.

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On 18.11.2017 at 7:15 PM, MR.CLEAN said:

if you find a metal that can flex as much as a carbon foil yet be resistant to cavitation (which tears up stainless props like concrete), let us know please!

There is nothing fully resistant against cavitation erosion.

But some materials are better than others. Seems that simple EPDM sheet is better than 316 stainless, or titanium or Ni-Al-Bz or duplex steels according to this: http://mickpeterson.org/Service/Grad/Grad_students/Thesis/Cavitation Erosion Thesis Final (Ken L).pdf 

Seems like a good source to me. And as an elastomer EPDM can flex far more than carbon laminate. Table for results of tested materials are almost at the end of document page 74/76 or 64 on paper version.

 

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11 hours ago, NotSoFast said:

There is nothing fully resistant against cavitation erosion.

But some materials are better than others. Seems that simple EPDM sheet is better than 316 stainless, or titanium or Ni-Al-Bz or duplex steels according to this: http://mickpeterson.org/Service/Grad/Grad_students/Thesis/Cavitation Erosion Thesis Final (Ken L).pdf 

Seems like a good source to me. And as an elastomer EPDM can flex far more than carbon laminate. Table for results of tested materials are almost at the end of document page 74/76 or 64 on paper version.

 

Very cool, very interesting.  Surprising that simple sheet rubber is about as good as anything.  Softer materials that can sustain impact with some give seem to be the key.

Basically EPDM rubber or BIOCOAT-A.

Could something so "soft" hold up for 40 days?

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5 hours ago, GauchoGreg said:

Very cool, very interesting.  Surprising that simple sheet rubber is about as good as anything.  Softer materials that can sustain impact with some give seem to be the key.

Basically EPDM rubber or BIOCOAT-A.

Could something so "soft" hold up for 40 days?

MRE = 0.72 mïcrometres / hour

40 days = 960 hours

0.72 mïcrometres / hour * 960 hours = 0.69 mm. And since MRE is the maximum rate of cavitation erosion, not average rate, the damage will likely be less than 0.5 mm.

So as far as cavitation is considered, it would work. Not so sure about abrasion effects of seawater.

If you read the whole article you'll see that rain erosion on helicopter blades are similar to cavitation. I got the impression they use elastomers on leading edges. if so, how long do they last?

Abrasion is obviously different, but seems info is there to be found for those who want to google it up. There are a lot more elasomers out there than those tested for that thesis, so something else might be even better.

Edit:

And lets not forget BIOCOAT-A allows to make repairs during the passage is necessary. Makes no difference for repair ability if damage is due to cavitation or abrasion.

Edited by NotSoFast
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its not a cavitation problem in any case, it was damage from impacts propagating through the foils.

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2 hours ago, rmb said:

its not a cavitation problem in any case, it was damage from impacts propagating through the foils.

Is It oficial?

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4 hours ago, rmb said:

its not a cavitation problem in any case, it was damage from impacts propagating through the foils.

If that is the case, do you think that is a easier or harder problem to address?

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On 11/20/2017 at 10:26 PM, jorge said:

HB and Comanche lack the Gitana speeds. Kite foilers don't manage forces involved in Gitana. IMHO not comparable.

Are you saying, that solid carbon, is weaker than a carbon foam design?.......

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Interesting that when they arrived home the port UptiP foil was still in place........

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7 hours ago, dachopper said:

Are you saying, that solid carbon, is weaker than a carbon foam design?.......

Not comparable, that's what I said.

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15 hours ago, rmb said:

its not a cavitation problem in any case, it was damage from impacts propagating through the foils.

Source? And what a coincidence to hit both foils and cause similar damage. Bad luck I guess. 

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10 hours ago, dachopper said:

Are you saying, that solid carbon, is weaker than a carbon foam design?.......

It may help if you do a little research into your engineering terms to frame the right question. Stiffness, tensile, compression etc help to narrow it down a little. 

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1 hour ago, mad said:

It may help if you do a little research into your engineering terms to frame the right question. Stiffness, tensile, compression etc help to narrow it down a little. 

I would be pretty shocked, if solid carbon was anything but stiffer, higher tensile strength and better compression than 2 x surfboard cored foil that broke.

 

Yes it would be heavier

 

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13 hours ago, Wess said:

Source? And what a coincidence to hit both foils and cause similar damage. Bad luck I guess. 

rmb has sources....

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On 18/12/2017 at 2:02 AM, Wess said:

Source? And what a coincidence to hit both foils and cause similar damage. Bad luck I guess. 

Or it could be the hard stuff they hit with both foils was just water..............its pretty hard stuff at 30 knots.

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