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Why isn't Titan classed? (2019)

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Re: Why isn't Titan classed? (2019)

#81

Post by foota »

stickfigure wrote: post #73
cbzoiav wrote: post #16

> The vast majority of marine (and aviation) accidents are a result of operator error, not mechanical failure. Could that be because the vast majority of mechanical designs go through processes designed to validate them and catch flaws? They also use SpaceX as an example. SpaceX ran a large number of unmanned launches to prove out the design before putting people on board. Several of those ended in loss of the vehicl…

The first space shuttle launch was crewed. It ended up with a ~2% failure rate. The Titan made about 50 dives. So, from a reliability perspective, on par with the shuttle. I posit that half the people on HN would volunteer for a hypothetical next shuttle flight without thinking twice.

Why go on the shuttle when you can go on the dragon?

Re: Why isn't Titan classed? (2019)

#82

Post by foota »

cactusplant7374 wrote: post #72
ajross wrote: post #37

Earlier quoted context omitted.

That's exactly it. If OceanGate had build and dropped a few dozen of these hulls empty, as many times as needed to reach failure, whatever design flaw caused the implosion almost certainly would have been noticed. It's the hubris of diving in what amounts to a prototype that's at issue here, not any fundamental technical mistake.

It had already been down quite a few times. Do you mean 100's of drops? Although, couldn't they just leave it at the bottom for a month and see if it implodes?

I believe the stresses of the hull going through changing pressures is relevant.

Re: Why isn't Titan classed? (2019)

#83

Post by sitic »

mjb wrote: post #62
AdamJacobMuller wrote: post #53

Earlier quoted context omitted.

As far as I'm aware, and please correct me if I'm wrong, they had never dove to this depth before. So, sure, it was launched before and recovered, but it never experienced the same conditions which caused the failure.

They did: http://web.archive.org/web/20200814020351/https://www.oceang... (At least twice, and probably more times).

Apparently it's at least 13 dives since 2021: https://www.geekwire.com/2022/beyond-the-titanic-oceangates-...

Re: Why isn't Titan classed? (2019)

#84

Post by hn_throwaway_99 »

Alupis wrote: post #42
cbzoiav wrote: post #26

Earlier quoted context omitted.

The craft survived several launches - that proved it can do it. Whether it can do it reliably / survive fatigue accross repeated cycles is a different question. Imagine we'll find out as the investigation progresses.

James Cameron gave an interview where he claimed the carbon fiber hull concept was tested by a team competing to get down to Challenger Deep at the same time his team was - and the concept failed in testing. He also claimed many within the deep submersible community wrote letters to OceanGate warning them their plan was flawed and would result in catastrophic loss. Specifically, the failure mode was delamination. I c…

That was a great interview IMO, thanks for posting. I think some people might find it hard to both convey sympathy and compassion for the deceased and their families as well as being adamant that the submersible design was nuts (especially since the man primarily responsible died), but I think Cameron in particular did that very well.

Re: Why isn't Titan classed? (2019)

#85

Post by [deleted] »

cactusplant7374 wrote: post #72
ajross wrote: post #37

Earlier quoted context omitted.

That's exactly it. If OceanGate had build and dropped a few dozen of these hulls empty, as many times as needed to reach failure, whatever design flaw caused the implosion almost certainly would have been noticed. It's the hubris of diving in what amounts to a prototype that's at issue here, not any fundamental technical mistake.

It had already been down quite a few times. Do you mean 100's of drops? Although, couldn't they just leave it at the bottom for a month and see if it implodes?

[deleted]

Re: Why isn't Titan classed? (2019)

#86

Post by quickthrower2 »

TazeTSchnitzel wrote: post #70

It's not classed because nobody would have signed off on it with the level of testing they had done. Carbon fibre reinforced polymers don't have a defined fatigue limit, so stress cycle failure can't be ruled out, and it's difficult to estimate how much a design based around that material can endure. To get certified, OceanGate would have had to do destructive endurance testing on a replica hull, but they only proved…

Having read enough plain crash stories, first thing I though of was material fatigue. Like in the early days fan blades snapping off jet engines causing catastrophic failure after so many takeoffs. Now they have to inspect these closely in manufacturing and during maintenance cycles. Wouldn’t surprise me if they use ML now as it seemed a difficult human observation task.

The stress/unstress cycle of a vessel going that deep must be immense.

Re: Why isn't Titan classed? (2019)

#87

Post by erik_seaberg »

deelowe wrote: post #77
cactusplant7374 wrote: post #72

Earlier quoted context omitted.

It had already been down quite a few times. Do you mean 100's of drops? Although, couldn't they just leave it at the bottom for a month and see if it implodes?

I thought the deepest it had gone was 3000 meters and there's no evidence of it even having been tested to 4k.

They had two successful trips to Titanic, and other tests in the Bahamas.

Re: Why isn't Titan classed? (2019)

#88

Post by jonathankoren »

"[F]or example, in the case of many of OceanGate’s innovations, such as carbon fiber pressure vessels"

This ain't the innovative win they thought it was. In fact, it's a self-own.

I recently saw a material scientist that specializes in carbon say there wasn't enough money in the world to get her to ride inside a carbon fiber submarine. Why? Carbon fiber has a very high tensile (i.e. stretching) strength. However, it's quite weak when under compression.

Guess which strength is important when operating in a high pressure environment?

Submarines, including deep submersibles, are kind of a solved problem. That doesn't mean there aren't risks involved, but when was the last time a submarine imploded above it's intended operating depth? The 1950s?

Re: Why isn't Titan classed? (2019)

#89

Post by hotpotamus »

hn_throwaway_99 wrote: post #22

> OceanGate’s submersibles are the only known vessels to use real-time (RTM) hull health monitoring. With this RTM system, we can determine if the hull is compromised well before situations become life-threatening, and safely return to the surface. This innovative safety system is not currently covered by any classing agency. > No other submersible currently utilizes real-time monitoring to monitor hull health during…

Honestly, the "real time health monitoring" felt like almost every tech "innovation" over the last decade or so - a half-baked excuse not to do things correctly. And when you can't switch your lights on because the cloud is down, it's inconvenient, but clearly the results of applying this thinking to critical safety are self-evident.

Re: Why isn't Titan classed? (2019)

#90

Post by pengaru »

cactusplant7374 wrote: post #72
ajross wrote: post #37

Earlier quoted context omitted.

That's exactly it. If OceanGate had build and dropped a few dozen of these hulls empty, as many times as needed to reach failure, whatever design flaw caused the implosion almost certainly would have been noticed. It's the hubris of diving in what amounts to a prototype that's at issue here, not any fundamental technical mistake.

It had already been down quite a few times. Do you mean 100's of drops? Although, couldn't they just leave it at the bottom for a month and see if it implodes?

> Although, couldn't they just leave it at the bottom for a month and see if it implodes?

No, cyclic stresses are a different animal altogether.

But considering it's just a matter of attaching ballast to sink it, dropping ballast to raise it, there's nothing preventing cyclic testing vs. static @ max depth over the same duration.

It seems obvious to me that you'd want to burn through a few test hulls characterizing the fatigue limits and verifying they are at least consistent hull-to-hull with a deterministic failure point you can plan for retiring before approaching.

You just need resources to burn on destroying enough hulls for the data.

And there's a rub there; as you inform the process via destructive iteration, odds are you'll first find the manufacturing process isn't even controlled/consistent enough to make progress on answering the "so how many cycles before go boom boom?" question until you've gone through a good chunk of runway figuring out how to even make it properly multiple times.

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