AC40

enigmatically2

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It shouldn't have happened, I know, but not the first time an engineering design has failed when pushed beyond normal limits or, apparently, well within normal limits
True, but there are mathematical formula that can be used in the basis of hours used and accidents occurred to assess the confidence that given a likelihood of a specified failure rate has been met. And on that basis the confidence would be negligible that this boat has met any credible likelihood.
So certainly in my field this would be considered unacceptable and non-compliant
 

david r

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But they sail with very little heel, so two rudders have no purpose.
The cats have 2 rudders and sail with windward heel. I'm thinking the extra RM allows the sailors push the boat harder while keeping windward heel, meaning more speed. So the windward rudder does serve a purpose.
Also given that a longer foil mast means higher flying, i'm wondering if the ride height could be determined by the main foils even with a longer rudder that was earlier suggested. Meaning the rudder foil would always be deeper under water than the side foils...less chance of breaking the rudder free.
There are probably good reasons not to make a longer rudder, and the cats also have a problem with the foils breaking free, just not to the same extent.
As far as adding lead goes, The original design concept was going to have enough lead to self right the boat IIRC. Don't the 40's have lead, or did they just build a giant dingy?
 

JALhazmat

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Reasons for not making a longer rudder

loads of drag, puts your down force way below your lift force making it massively unbalanced, there is no point as it isn't what the rule set dictates

reasons for not having twin rudders

even more drag, even more downforce throwing balance with the lifting foil way out

the rudder let go when it got too high, it would now be two rudders letting go at the same time.

the cats have twin rudders but 9 meters apart( or something huge) pulse run massive rudder differential with the windward one angled down to aid righting moment

imoca monohull have twin rudders, and kick up the one not in use, don’t have foils on them so aren’t doing the same job as these.

it’s just a bad idea imo
 

Stingray~

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i'm wondering if the ride height could be determined by the main foils even with a longer rudder that was earlier suggested. Meaning the rudder foil would always be deeper under water than the side foils...less chance of breaking the rudder free.
bingo
 

shanghaisailor

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It hasn’t been pushed as a prototype. Every team was required to buy one “as is” and then use them for races crewed by sailors who do not have experience in this type of boat. The boat has auto pilot features that allows inexperienced sailors to crew them. They are even offered for sale to the public!

Also, the recalls are not applicable to this situation. The have 20 incidents in 600,000, that is 0.00003%. The AC40 has broken its bow on 100% of the boats.
Oh dear - another English lesson required

Prototype : a first or preliminary form from which others are developed or copied

In this case the prototype "the first or preliminary form" has proven that there is insufficient strength in the bow to withstand such an incident so the design will be "developed" rather than just "copied".

Your comment about the % of recall is not logical. Clearly Ford consider the 20 incidents to be "SO FAR!" otherwise they wouldn't be recalling the 620,000 (-20) that haven't caught fire yet so they are totally applicable.

Having discovered - rather dramatically - this weakness on the prototype/first/hull one this early means they have 1 repair; 1 recall or strengthening on site - (INEOS) and a re-design and strengthening of subsequent hulls before they leave McConaghy Yachts and ALL to the same technique and with the same materials to protect the one design concept

This sort of situation is not unique in the boatbuilding world, let alone the wider engineering world. Titanic, Sail-Rocket's dramatic somersault and Team Phillips Atlantic breakup to name just a few along with multiple other projects pushing known boundaries.

How they deal with the failure and the measures they take to investigate and rectify the problem will be interesting to see.
 
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smackdaddy

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Oh dear - another English lesson required

Prototype : a first or preliminary form from which others are developed or copied. In this case the prototype "the first or preliminary form" has proven that there is insufficient strength in the bow to withstand such an incident so the design will be "developed" rather than just "copied".

I think you’re reaching a bit here Shang. This wasn’t a “prototype” in the true sense of the word (even by your own definition) because several other boats using this exact spec were ALREADY being delivered and/or being built for delivery. And now they all have to change because of fundamentally poor design/construction.

If you’re going to give English lessons, at least make them accurate.
 

enigmatically2

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Obviously the same in Ford Motor Company's field too. Just 20 incidents and they are recalling 600k+ vehicles
All car companies have recalled vehicles. When you are producing hundreds of thousands of vehicles and they are used over years, then they are bound to find problems that weren't experienced in testing.

The difference here is that NZ went into production before they had done any testing on a pre-production prototype.
And this was a catastrophic failure. If they had produced a prototype and tested it for 6 months and this hadn't occurred, but later did then fine. But that's not the case.
If this was so badly wrong, it also opens the question as to what other gremlins are lurking
 

Jethrow

Super Anarchist
AC40 is an OD has been delivered to customers. The whole point of a production OD is that it is not a first or preliminary form. Each is supposed to be the same as the others.
Yes, the fact that it is mandatory to purchase as part of entry in the event has an attached expectation that it is up to the jobs at hand. You can't mandate this boat on another entity and then say "Well, we're just figuring it out, let's see what happens if we try this!"

It's all well and good for the NZ fanboys to try and pass this off as a testbed hull that the other teams will have to deal with but this is just not the case!

TNZ has inadvertently screwed the pooch on this one.
 

shanghaisailor

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All car companies have recalled vehicles. When you are producing hundreds of thousands of vehicles and they are used over years, then they are bound to find problems that weren't experienced in testing.

The difference here is that NZ went into production before they had done any testing on a pre-production prototype.
And this was a catastrophic failure. If they had produced a prototype and tested it for 6 months and this hadn't occurred, but later did then fine. But that's not the case.
If this was so badly wrong, it also opens the question as to what other gremlins are lurking
First of all please don't think I am defending what happened but you have a point, shows what can happen even when a set of qualified designers get it right - they think!

I also agree it will have knocked the confidence of the other teams in pushing this platform to the full. I would be more concerned if it was given to less experienced sailors.

AC40 is an OD has been delivered to customers. The whole point of a production OD is that it is not a first or preliminary form. Each is supposed to be the same as the others.
I agree and now any changes either or both to the design and usage limits will have to be replicated across all the boats, perhaps even to not allow the auto-pilot to be switched off especially in less experience hands (not saying it was inexperienced guys that stuffed it in by the way.)

As far as I am aware only one other has left the factory. Not a good look and especially embarrassing given all the (so far) hype about how suitable it is for the two series for the Women AC and Youth AC.

I think you’re reaching a bit here Shang. This wasn’t a “prototype” in the true sense of the word (even by your own definition) because several other boats using this exact spec were ALREADY being delivered and/or being built for delivery. And now they all have to change because of fundamentally poor design/construction.

If you’re going to give English lessons, at least make them accurate.
Actually AFAIK only one other delivered so far but I agree - good job actually ( I don't think Alinghi's has left the factory yet) imagine if all the teams already had their boat(s) and worse yet, what if someone had got hurt, sadly failures at high speed have been known to be fatal in the past

I do find it ironic though that when American Magic almost sank for a similar under-engineered part of the boat failing in an unexpected incident people didn't seem to be so keen to get the knives out for THEIR design team.

And the English lesson wasn't from me and neither was the definition, it was from Merriman-Webster & Oxford ;-)

Makes for an interesting discussion though

Cheers

SS
 

enigmatically2

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I do find it ironic though that when American Magic almost sank for a similar under-engineered part of the boat failing in an unexpected incident people didn't seem to be so keen to get the knives out for THEIR design team.

And the English lesson wasn't from me and neither was the definition, it was from Merriman-Webster & Oxford ;-)

Makes for an interesting discussion though

Cheers

SS
I think there are a couple of major differences between this case and AM
1) In this case it is a OD, no-one is trying get an advantage from weight saving etc. When they are like AM (or F1) then it is more understandable
2) It was AMs choice, their risk. Here NZ are designing for teams that have had no input, no choice (even whether to buy at all). That is a wholly asymmetric relationship
 

The_Alchemist

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Oh dear - another English lesson required

Prototype : a first or preliminary form from which others are developed or copied

In this case the prototype "the first or preliminary form" has proven that there is insufficient strength in the bow to withstand such an incident so the design will be "developed" rather than just "copied".

Your comment about the % of recall is not logical. Clearly Ford consider the 20 incidents to be "SO FAR!" otherwise they wouldn't be recalling the 620,000 (-20) that haven't caught fire yet so they are totally applicable.

Having discovered - rather dramatically - this weakness on the prototype/first/hull one this early means they have 1 repair; 1 recall or strengthening on site - (INEOS) and a re-design and strengthening of subsequent hulls before they leave McConaghy Yachts and ALL to the same technique and with the same materials to protect the one design concept

This sort of situation is not unique in the boatbuilding world, let alone the wider engineering world. Titanic, Sail-Rocket's dramatic somersault and Team Phillips Atlantic breakup to name just a few along with multiple other projects pushing known boundaries.

How they deal with the failure and the measures they take to investigate and rectify the problem will be interesting to see.
Put down the shovel and stop digging yourself into a hole.

You are the only one that has ever used the term prototype in any description of the AC40. NZ has never called it a prototype. Using a dictionary to justify your use of the word doesn’t make it correct.

With this happening to the first hull it could be easy to assume it is a prototype test hull, but it is not. NZ decided to put the design into full production without any testing of the actual boat. They already have built, billed and shipped a couple of other AC40’s.

Ford wants customers to know that they will fix any safety issues that arise with their products, it helps future sales and keeps government regulators away. Completely different issues. Does McConaghy Yachts recall your boat after five years to fix a forestay that make break and could cause the mask to fall and injury someone In 0.0003% of boats?
 

Forourselves

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I think there are a couple of major differences between this case and AM
1) In this case it is a OD, no-one is trying get an advantage from weight saving etc. When they are like AM (or F1) then it is more understandable
2) It was AMs choice, their risk. Here NZ are designing for teams that have had no input, no choice (even whether to buy at all). That is a wholly asymmetric relationship
In other words, the damage itself isn't the problem. The "relationship" is, as it has always been. Take the damage out of the equation as the solution has been designed and is about to be implemented, and what do you have left? the same old tired argument about unfair blah blah blah. You're going to keep flogging the dead horse until you're blue in the face.
Get over it.
Team NZ's track record of designing fast boats is second to none. Certainly better than most if not all current teams track records. Te Rehutai was a generation ahead of every other boat in the last cup. That design team is the best design team in the game and has been for a long time. Given their record, knowledge and experience, It makes sense that Team NZ's design team be the design team to produce the AC40.
 

david r

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Thanks for responding to the rudder length question JAL.
I would argue that a little bit longer rudder would not add that much drag, but i know that too long a rudder would deflect under pressure and that deflection may interfere with the usefulness of the foil below. Also i doubt it would effect balance that much for the rudder foil to be deeper. Airplanes have the back foil which provides down force at all different heights relative to the wings.
Speaking about balance brings up the question of "does the main foil being way off to the side relative to the rudder foil create a balance problem"?
 

Stingray~

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I would argue that a little bit longer rudder would not add that much drag, but i know that too long a rudder would deflect under pressure and that deflection may interfere with the usefulness of the foil below. Also i doubt it would effect balance that much for the rudder foil to be deeper. Airplanes have the back foil which provides down force at all different heights relative to the wings.
Good analogy. The lift vector, basically vertical, means that a longer rudder would make no difference to the balance compared to the rudder-foil's effect at the current length. Were I to use the AC40 as an LEQ, a longer rudder is something I'd seriously consider using for safety.
 


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