Tourist submersible visting the Titanic is missing 101

[SnTMan]

Suspended operation, due to.... Out of subs

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[dik]

Maybe customers might be a tad reluctant?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[sgw1009]

Titan Specs, including description of communications and navigation systems:

https://ocean-archives.github.io/

 

[Tomfh]

sums it up, and you forgot to include that he fired anyone that didn't agree with him. 'De mortuis nil nisi bonum dicendum est' (don't speak ill of the dead) is not applicable... the guy was a POS and killed four others.

I’m not sure anyone’s saying don’t speak ill of him. He was an arrogant guy who rode roughshod over safety. He was at the centre of it all.

However he doesn’t carry the entire blame. There were plenty of people who *didn’t* disagree with him and happily pursued the venture with him. Plenty of people supplied to him, including it seems the main hull for the specific purpose of exploring at Titanic depth. Do we just ignore all that and pin all the blame on Rush and Rush alone?

If we ignore the big picture and reduce the story to Naughty-Stockton-Rush—a-Bad-bad-thing we will miss a lot of the important factors that lead to disasters like this.

 

[1503-44]

Well they do sell dynamite to miners and AR7s to almost anyone. The trick is not to do things with them that are dangerous to anything other than rocks and bulls eyes at the shooting range.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[jrs87]

OceanGate had modest intentions with Cyclops 1. Then with Titan (Cyclops II) the CEO extended ambitions by simply scaling up. It seems tourist visits to the Titanic was tacked on. In the end, the project was over-extended. Parts of the process were done in reverse. Mission creep failure.

https://youtu.be/qagXxMp7Aow

https://www.oceangatefoundation.org/expeditions/titanic-expedition/

I'm personally curious how the hinged hatch titanium to titanium bolted seal worked. Is wisely seems to have not depended on O-rings. It would have to be kept very clean and ding free.

 

[human909]

FoS of 2.5 implies that you understand the material extremely well

Your definition of FoS might be different from mine and your area and methods of practice might be different... However I would not describe a FoS of 2.5 as implying that you understand the material extremely well. I'd say that it is the opposite. 2.5 is a relatively large factor if it is a material factor alone.

(Some FoS values used in non LSD (LRFD) also include load amplification factors, but in which case you are talking about variability of loads not just the material.)

 

[IRstuff]

There were plenty of people who *didn’t* disagree with him and happily pursued the venture with him. Plenty of people supplied to him, including it seems the main hull for the specific purpose of exploring at Titanic depth

But, none of them worked for the company, or were quickly fired, or knew enough to not touch the company with a 4000-m pole. That is why he hired young, inexperienced engineers, since they would not know enough to know that this was not a good thing to do without adequate and thorough testing.

Oh, this is so cool; SOMEONE is using Mathcad and it's actually published

https://www.engineering.com/story/ill-fated-titan-submersible-was-based-on-an-unproven-design

Some useful information in the references in the article

https://web.archive.org/web/20210804224656/http:/

http://www.compositesworld.com/articles/composite-submersibles-under-pressure-in-deep-deep-waters

https://www.compositesworld.com/articles/deepsea-submersible-incorporates-composite-pressure-capsule

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[Tomfh]

So we just ignore the actual designers and builders of the hull do we?

 

[SWComposites]

Well its not really clear who did the actual overall pressure shell design: tube + end rings + end domes + window.

And everyone presumably involved has been very quiet, probably at direction of their lawyers.

Though it appears Spencer was not contracted to test the composite tube design. And the apparent fact they used an FEA code, and one not well known for use in composite structures, is very troubling. Then there is the apparent fact that they used a combination of wet wound hoop layers and prepreg axial plies means two different epoxy resin were mixed, and it sounds like they used a very slow (not standard) cure cycle - all of which is also very concerning. Which might be the reason there are reports that the tube had a high level of porosity.

Hopefully a lot more facts come to light at some point.

 

[TugboatEng]

I wonder if the carbon fiber cylinder would be able to support itself without the titanium end caps? In the pictures I have seen that it appears as if the bond at the cap to cylinder failed. On the titanium flange I see epoxy in some areas and bare titanium in others. If the epoxy separates from the titanium would that allow the shell to collapse?

Otherwise, if the shell failed first the deflection could pull the epoxy off the surface of the flange.

 

[Tomfh]

I wonder if the carbon fiber cylinder would be able to support itself without the titanium end caps?

No. The cylinder required the titanium domes for overall stability, so as to brace the hull against buckling. An unstiffened cylinder is far less stable than a stiffened one.

I did some quick numbers based on an infinite cylinder the size of the hull, and the buckling load isn't even close. It needs the domes. Submarines have ribs and similar things for the same reason.

With a stiffener at each end the hull's theoretical buckling pressure increases to ~2-3x the pressure at which it failed (based on crude approximate methods).


EDIT: Correction to above. A ideal carbon cylinder has a higher theoretical buckling pressure than the pressure where failure occurred.

 

[SwinnyGG]

The thing worked 40 or so times, so wasn't a completely failed program. It's about the same failure rate as the space shuttle.

40 or so times, including dozens of shallow depth test dives to test things like thrusters and ballast systems

It went to test depth a total of 8 times. It only came back 7.

I digress.


Personally, I'm convinced that the failure was very likely due to failure of the window. We're spending an awful lot of time talking about the carbon fiber hull; I'm not saying we shouldn't be, and I'm definitely not saying that the carbon fiber parts of the system were designed appropriately, tested appropriately, engineered or manufactured correctly. But the hull was, in theory, designed for this depth and had some level of safety margin.

The window was literally not designed for this depth, and not properly evaluated by its end user when it came time to determine depth rating. I'd be looking to eliminate that before I started down the hull rabbit hole.

 

[LittleInch]

It's just difficult to see how window failure is going to lead to implosion and complete disintegration of the the hull.

Instant death just the same from pressure, but the craft should have then just filled with water and sunk to the bottom of the ocean floor.

although it was only "rated" for 1350m, I think that had a larger FoS on it (x6?) than the hull did and seemingly showed no signs of distress.

the CF hull on the other hand....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SwinnyGG]

It's just difficult to see how window failure is going to lead to implosion and complete disintegration of the the hull.

Disagree.

Failure of the acrylic window would have resulted in a 15" diameter jet of seawater shooting directly down the long axis of the pressure hull at extreme speed. This would blow the end bell at the far end right off, and release a huge amount of energy due to the water hammer resulting from the collapse of the remaining bubble of air inside the hull.

This was not like a leaky submarine in the movies where there's a little drinking fountain stream of water coming through the joint. This is literally an explosion in reverse.

 

[Murph 9000]

But the hull was, in theory, designed for this depth and had some level of safety margin.

In theory, yes. The unknowns are whether there were any latent manufacturing defects which could have compromised the design strength, and how much damage had been done to it by the cyclic fatigue of the previous deep dives. The lack of non-destructive testing both after manufacturing and after each deep dive, combined with the highly experimental nature of CF being used in this application, calls the strength of it into question at the start of the final dive. If the reported large bangs were fractures or delamination spreading through the structure, the hull is a highly likely point of eventual failure.

 

[IRstuff]

But the hull was, in theory, designed for this depth and had some level of safety margin.

The design was based on design data not specifically intended for this application and on theoretical safety margins. In one of the many articles about this incident was the notion that other vehicles used a factor of 12 FoS based on test results specifically intended mimic underwater environments, so design data based on relevant testing, and a substantially higher FoS, neither of which were used for the Titan.

This was an untried and untested design, so FoS of 2.5 or 2.25 was just plain silly. FoS that low should have only applied to well-used, well-tested, materials with tons of testing and field experience. And even then, this was a life-critical application where a single point of failure means death.

It's likely that the dome was designed with a much higher FoS and possibly the 12:1 value, since that was off-the-shelf, so it's likely that it wouldn't have failed.

TTFN (ta ta for now)
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[SwinnyGG]

Just so we're clear gents - I'm not saying "The hull is good, no way it's root cause, failure could only be at the window"

Agree 100% with all the concerns in this thread about the design of the hull, I just think there's also a significant probability that the acrylic window was the point of initial failure, and we're not talking about that at all.

If you want to talk safety factors - the safety factor as-designed for the hull is 2.5 or so. The safety factor as rated for the acrylic window is/was 0.3.

My own personal back-of-the-napkin guess at the probabilities here is that I'd guess 60/40 or 55/45 window vs hull as point of initial failure.

 

[CWB1]

So we just ignore the actual designers and builders of the hull do we?

I suspect blaming the dead boss will be the regulators' and lawyers/courts' decision unless Rush's family spends many cubic dollars in court blaming others.

 

[LittleInch]

Diagree about the safety factor for the window though at 0.3. The ratio of actual to rated was 0.3, but the FoS would have been a lot more than 1 at 1350m rating. We don't know what it is and it could have failed, but its low probability for me at the moment.

Lets wait and see if we ever find out?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.