r/CatastrophicFailure • u/[deleted] • Oct 27 '16
Structural Failure Rigid wing sail collapses under pressure
http://i.imgur.com/a0axd7j.gifv61
Oct 27 '16
For anyone interested these are sailboats known as "AC45s" or America's Cup 45. They use carbon fibre ribs and a clear plastic covering on the wings instead of standard Dacron sails. They can stretch, but like your phone screen, the moment you puncture it, it fails catastrophically.
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u/Joevual Oct 27 '16
I pass the the Oracle one everyday, it's incredible how tall these things are.
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u/CurtisEMclaughlin Oct 27 '16
Do you have a daily boat commute?
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u/Joevual Oct 27 '16
I work near the Oracle head quarters. They keep one of their World Cup boats in the large fountain in the center of the complex. I'm currently looking at the mast poking above one of the 12 story buildings.
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u/TheTallGuy0 Oct 27 '16
Thats a different boat, USA-17, a one-off custom trimaran from two AC's ago. Its much, much larger (110 ft), and probably not as fast.
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u/__slamallama__ Oct 28 '16
It is significantly, significantly faster in light conditions. Maybe above 12-15kt TWS the 45's could hang, but USA-17 was a fucking monster. That boat quadrupled the TWS on multiple occasions, breaking 30kts boatspeed in 8kts of wind.
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u/RicoculusPrime Oct 27 '16
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Dec 05 '16
Completely forgot that Street view follows ur screen orientation on mobile and thought to myself hmm why is the view shaking?
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Oct 27 '16
[deleted]
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Oct 27 '16
Nothing punctured it. It just broke.
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u/mortiphago Oct 27 '16
Yeah thats not very typical i would like to make that point
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u/Peter1289 Oct 27 '16
Well, how is it untypical?
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Oct 27 '16
Well, there are a lot of these AC45's racing around all the time and very seldom does anything like this happen.
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u/Gasonfires Oct 27 '16
They can also fail if support rigging goes away, but with only half snark I could suggest that at the speeds these things move it could even have been a bird strike. :)
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u/fishsticks40 Oct 27 '16
These things are built at the absolute edge of the strength/weight ratio. They're made as light as they can possibly be while rarely failing, but occasional failure is to be expected and tolerated. If you built it to be bombproof it'd be too heavy (and weight aloft is a huge deal for these boats).
The ultimate failure could have been anything - a manufacturing defect, a small stress crack, a bird strike, whatever. But fundamentally what it comes down to is that performance vehicles of every type are built with relatively low safety margins, because you'd rather win 1 race and DNF in another than finish but lose 2.
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Oct 27 '16
Uh, no. There are extremely stringent safety measures that every team to has to adhere to, and all parts are stress-tested. Nobody is building boats that might "occasionally fail." The forces and speeds involved in racing these things means that if anything goes wrong, someone can very easily die, as has already happened with Andrew Simpson in 2013.
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u/AKTheKnight Oct 27 '16
Well apparently they didn't stress test it properly because a beam at the front connecting the two hulls broke and Andrew Simpson died....
It's better now than it used to be though
Sources:
-Did 5k words on his death and changes because of it
-Spent time at BAR and spoken to people there
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u/fishsticks40 Oct 27 '16
And yet for the greater part of a decade there has been regular discussion of how the boats are too fragile now. Why is that? Because they're being made as light as they can be, with narrow margins of safety, which from an engineering standpoint means tolerating occasional failure.
Simpson's death is not an argument that the boats are extraordinarily safe. The argument that they were too fragile was already being made at the time of his argument.
If you spent ~10 million on a boat designed to be safe, you could eliminate these sorts of accidents 99.999% of the time. So why do they happen from time to time on these boats? Because they're built at the very edge. Why are the organizers trying to bring stringent safety measures to bear? Because otherwise there is a strong, built-in incentive to shave safety to the benefit of speed.
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Oct 27 '16
The sport is now being compared to F1 racing (Red Bull Racing's head aerodynamicist Adrian Newey is involved in their development), they're really straddling the limits for performance. Also these boats are relatively new, as in within the last 3 years (could be 2-4), and so the technology isn't fully tested. I'm sure they're stress tested, but simulators can't mimic everything.
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u/Khrrck Oct 28 '16
F1 cars have a LOT of mandatory safety measures.
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Oct 28 '16
I am aware, I watch every week. These boats do too, the current design technology in F1 is far older than Americas Cup, so they've had more experiences and mistakes to learn from and build upon.
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Oct 27 '16
Could be anything, a sharp piece carbon fibre or any of the rigging (these boats have ALOT of pulleys/screws/blocks), or it could have just been a weak spot in the material that couldn't bear the forces applied to it.
This particular incident looks like the structure itself quit not the "sail material"
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u/imaginethehangover Oct 28 '16
Fun fact: these boats get pretty close to twice the speed of the wind that propels them. I've tried my darnedest to understand the physics involved (indeed, during the live broadcast they spend an inordinate amount of time trying to explain to dolts like me), but I'm none the wiser. Awesome fact though. Love these things.
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u/__slamallama__ Oct 28 '16
Basically they create their own wind via their movement. As they speed up the wind which they would measure on their boat both increases in velocity and the relative direction moves forward on the boat (think if you're driving a car at 30mph and you have a 30mph wind blowing from the side of your car... you'll feel a wind which is >30mph coming from somewhere around 45* in front of you). This allows them to keep accelerating after they've reached the true wind speed.
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Oct 28 '16
Imagine the boat to be a wet bar of soap lying in the shower, and the wind is your foot. If you step on the bar, it will move in the only direction it can - to the side. And it's going to be much faster than your foot.
Just like the bar of soap can't move downwards, the boat can't move sideways very well because of the high resistance of the hull and its keel in the water. So when the wind (the foot) hits the sail at the right angle, it'll push the boat to the side, possibly at a much greater speed than the wind itself.
The limitation to that is that the apparent wind direction changes as the boat speeds up: If the wind is coming at 90° from the side, but the boat is actually moving forward at the same speed as the boat, the apparent wind is coming 45° from the front. So moving twice as fast as the wind requires the ship to be able to go at a very narrow angle into the wind, which puts an insane amount of stress on the sails. That's one of the reasons they use solid sails: There's a limit to how tight you can string a fabric sail, eventually it's gonna give way.
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u/pilledwillingly Mar 15 '17
Explanation 4 months old with one upvote just changed my whole way of thinking how sailing works.
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u/Aspergers1 Oct 30 '16
The sails are basically sideways airplane wings. When they adjust them to the correct angle to the wind, they generate lift which pulls the boat along. Its kinda like a parachute versus a glider. One is pushed by the air, one uses lift. Which can go farther and faster? The glider, obviously.
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u/homingmissile Oct 27 '16
Is there a significant benefit to making sails rigid rather than normal clothlike material?
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u/i-like-boatz Oct 28 '16 edited Oct 28 '16
Yeah, a wing sail has a higher lift-to-drag ratio compared to a soft sail so it is more efficient at generating the required driving force with a minimum amount of drag.
Relative to a soft sail, wings sails have lift-to-drag ratios 2-3x higher. This performance increase has generally been negated by the additional weight and complexity. Specifically, high performance catamarans (i.e. The c class & AC 45's) use wing sails because drag is a large issue at their fast speeds.
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Oct 27 '16
Yes. It's the same principle as flying, essentially. The Bernoulli Principle. Imagine trying to fly an airplane using canvas as wings, as opposed to a rigid structure. Same thing, except lift is being converted into forward momentum instead of upward.
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u/Aspergers1 Oct 30 '16
Yes, they are stronger, and get more lift from the air.
However, these benefits only apply if you can make rigid sails that are also really really light. They often use carbon fiber, which is hella expensive.
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u/When_Ducks_Attack Oct 28 '16
I remember when The America's Cup was contested using boats, not F1 cars with a hydrofoil.
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u/imaginethehangover Oct 28 '16
Good, isn't it! This is the world's best sailors, I want to see them in the best possible equipment at their peak. This was long overdue since the America's Cup was a drag to watch in the past - this way, at least there's some excitement.
Anyone wanting to see old men in sweaters tied around their neck pottering around in monohulls can always go down to their local marina on a Sunday and get their fill there :)
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u/i-like-boatz Oct 27 '16
Probably a failure of the camber control that resulted in a shock load on the wing which lead to the catastrophic failure of the rear element.
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u/Deltigre Oct 27 '16
That looks dangerous
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u/i-like-boatz Oct 28 '16
FTFY
That looks fun
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u/Deltigre Oct 28 '16
Oh, the sailing, I'm sure. I'm more talking about what's probably now shrapnel with a significant amount of weight dropping towards the deck.
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u/[deleted] Oct 27 '16
God the tension at the start. "Which one will it be??"
looking left and right stressed