Titanic submersible

[John McNamaraParticipant @johnmcnamara74883]

A sad day, a loss of 5 people affecting many families and friends.

From what I have read a large percentage of the craft was carbon fibre, made into a pressure vessel, in this case the hydraulic force applied to the vessel was on the outside skin. Does this mean the strands of carbon fibre within the epoxy binder forming the walls of the vessel are in Compression?

Most carbon fibre pressure vessels used today contain pressure on the inside of the vessel, the strands of carbon fibre within the epoxy binder forming the walls of the vessel are in tension, usually referred to as the hoop stress.

This makes me wonder if carbon fibre in an epoxy binder making a composite material has superior mechanical properties to say steel or titanium in compression? Epoxy being a plastic will creep under a moderate load if used alone. So what happens to a composite material made from carbon fibre and epoxy when the force is on the outside of the walls. The hoop stress is reversed.

I can only wonder what material physics are at play? if the epoxy binder were to creep as I think it will, the carbon fibre layup (There will be many layers of strands or cloth) might even be subjected to buckling, a common failure mode for columns. Or delaminating. I also assume that the pressure vessel is not completely symmetrical no doubt there will stress concentrations in particular areas.

Maybe a structural engineer in the forum could put my (amateur analysis) right.

[Bill PhinnParticipant @billphinn90025]

Posted by Nigel Graham 2 on 23/06/2023 01:19:

– “The remark about the claim that the Titanic was "unsinkable" is so crassly repeated over and over again. No-one at the time who actually knew anything about ships ever said that! It was a foolish mis-interpretation by some newspaper hack,”

 

Sorry, Nigel, you’re not being completely fair there, though maybe I wasn’t either. I stand nevertheless by my interpretation [shared by many others] that the hubris of suggesting Titanic was unsinkable is at least part of what makes this episode in history so compelling for so many.

“The idea that the ship was unsinkable was advanced by newspaper and magazine articles as well as by advertisement materials from the shipping company.”

“The claim actually made [by the builders and owners of Titanic] was that she was 'practically unsinkable', close enough, but nevertheless an unfortunate statement and one which would haunt both builder and owner for years.”

EtA: Here’s another source showing “a White Star Line publicity brochure produced in 1910 for the twin ships Olympic and Titanic which states ‘these two wonderful vessels are designed to be unsinkable’.”

Posted by Mick B1 on 22/06/2023 20:27:57:

“My missus and I actually did visit the Somme battlefields twenty years ago or so. After looking at the crater at La Bosselle (?), and High Wood, and chatting to a collector delighted with the shrapnel balls he'd picked up, we both began to feel there was something parasitic about wallowing in imagined emotions of those caught up in lethal events over which they'd had little if any control. We felt creeped out, and shortened the time on the Somme in favour of visiting relatives in the Vendee.”

Thanks for your reply, Mick. I'm sorry to hear how your visit to First World War battlefields was spoiled by the insensitivity and mixed-up priorities of some of the people you met there.

I think on balance more good than harm comes from such visits, because they can bring home to people, in a way the history books can't, the appalling scale of human slaughter we have inflicted on ourselves as a species, and decrease the chances, in some quarters at least, of catastrophes of the same kind happening again.

In the present case, I'm sure valuable lessons will be learned from the terrible misfortune of these five people – lessons that in the long term may benefit unknown numbers of other people, however indirectly.

 

Edited By Bill Phinn on 23/06/2023 03:54:25

[jimmy bParticipant @jimmyb]

Fulmer you are a vile person.

Blocked.

Jimb

[JasonBModerator @jasonb]

Lets forget the personal comments, anymore and the thread gets locked, We are all entitled to a view.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John McNamara on 23/06/2023 02:23:04:

[…]

Maybe a structural engineer in the forum could put my (amateur analysis) right.

.

I cannot claim to be a structural engineer, John … but I do have some first-hand personal experience of a catastrophic failure of a composite panel, which I will share later.

The pressure involved was trivially small compared with the Titan event, but the effects were certainly dramatic.

The pressures at depth are easy to calculate, but almost incomprehensible … but the story that I linked yesterday, about the Acrylic window, gives us some sense of the effect on a known material !!

MichaelG.

[Justin ThymeParticipant @justinthyme24678]

Posted by John McNamara on 23/06/2023 02:23:04:

A sad day, a loss of 5 people affecting many families and friends.

That is about the same number of people killed on the UK roads every day, and that rarely if ever makes the news. And most of those who die venturing onto our roads did not believe they were taking any risk, often killed by others breaking the law.

The folk on this submersible were on a great adventure knowingly doing something phenomenally dangerous. I take my hat off to them for their spirit of adventure, but should we feel more sadness than we do for all the other deaths As usual the media is sweeping us along, controlling what we think and what we should be sad about.

[Michael GilliganParticipant @michaelgilligan61133]

John …

I’ve just found this: **LINK**

https://www.science20.com/hontas_farmer/ocean_gates_titan_submersible_a_suboptimal_shape_and_a_tragedy-256678

It’s low on detail, but the logic seems reasonable enough.

MichaelG.

.

Edit: __ See also https://news.ycombinator.com/item?id=36392416

Edited By Michael Gilligan on 23/06/2023 08:20:07

[PeroParticipant @pero]

A very sad outcome and my sympathies to all family and friends of the deceased.

Back to the comments re the cost of the rescue attempt. The oceans of the world are divided into areas of national responsibility. Within those areas the responsible country ( usually that adjacent ) has responsibility for undertaking marine rescues. I believe this is covered under international maritime law or agreement. It answers why Australia on occasion mounts rescues deep into the Southern Ocean to rescue disabled yachtsmen. The costs are very high and occasionally involve the rescue of only one person. Rescues of ill or injured personnel from commercial vessels are also undertaken on a more frequent basis.

I am very confident that the same applies in the UK, based on the documentaries I have seen, and in other maritime nations around the world.

With respect to the difference between this attempted rescue and people smugglers and their clients, the smugglers do not advertise departure dates and destinations and frequently it is only when disaster strikes that the authorities are made aware of the situation, and not by the smugglers.

Quite different to the current situation.

The cause of the present disaster is something hopefully we will learn in due course and can benefit from for the future.

I understand that the submersible has made this trip ( safely&nbsp on a number of previous occasions so the design is not inherently unsafe but it may have exceeded its safe working life due to fatigue. We shall have to wait and see. Anything else is pure conjecture.

Pero

[Michael GilliganParticipant @michaelgilligan61133]

If accurate, this is not good:

**LINK**

https://abcnews.go.com/US/company-lost-titanic-overstated-details-partnerships-boeing/story?id=100256217

MichaelG.

[Neil WyattModerator @neilwyatt]

Guardian mentioned that those companies deny association with Titan design. But they did work with them on the predecessor craft.

[Neil WyattModerator @neilwyatt]

I share the scepticism that carbon fibre is a good choice. I have a carbon fibre loudspeaker cabinet, the design is claimed to be the lightest 2×12 cabinet made. While it is very light and sounds incredible, it is not as robust as a ply or even mdf cab would be.

Carbon fibre composites are best in tension but are vulnerable to damage. In this case the hull dedign must have been able to take the stresses of the dive, but was it able to cope with the strain associated with repeated pressure cycling?

[FulmenParticipant @fulmen]

This was a cowboy operator with no regard for safety. The founder was even quoted as saying that current regulations "needlessly prioritized passenger safety over commercial innovation"…

[Roger Williams 2Participant @rogerwilliams2]

The sub would implode at something like 2200 ft per second and the poor souls would be incinerated and turned to dust in about a millisecond , which is a lot quicker than you can blink your eye !!. The human brain would react to this in something like 150 milliseconds. Jesus..

[HopperParticipant @hopper]

I would be a bit suspicious of the area where the carbon fibre cylinder joins the two titanium end domes. Seems like the variation in the way the two materials behave under repeated compression/decompression cycles could become an issue over time. The sub had made at least a dozen previous dives to the Titanic so it may be something that only showed up after repeated cycling, as often happens.

It was reported somewhere, which I can not find now, that the vessel had been pressure tested by a lab in the US. No further details, but it would have to be some test rig to fit the 20-foot long pressure vessel into it and then submit it to the kind of 6,000psi / 400 Bar pressures at Titanic depths. And I wonder if they would have done like with steam boilers and hydrostatically tested it to double the working pressure? 12,000 PSI / 800 Bar. That would be one heck of a test rig.

The company's over-inflated claims of NASA and Boeing etc involvement carry a whiff of salesmanship over sound and cautious engineering. I am sure things will become clearer in the ensuing investigation.

But there certainly are ironic loose parallels to the original Titanic disaster: Exaggerated claims of invincibility, pushing on in the face of expert advice not to, and a bit of a lack of planning for if the unthinkable actually happened. Sad business all round.

[HopperParticipant @hopper]

Posted by Roger Williams 2 on 23/06/2023 09:39:05:

The sub would implode at something like 2200 ft per second and the poor souls would be incinerated and turned to dust in about a millisecond , which is a lot quicker than you can blink your eye !!. The human brain would react to this in something like 150 milliseconds. Jesus..

Yes the physics of the situation are mind boggling to try to grasp. That is about twice the speed of sound. Incinerated? Under water? At 2C? Bizarrely could be possible. The air inside the vessel being compressed at that rate would get very hot. And kinetic energy involved would be massive. Look at pictures of old locomotive boiler explosions at, what 100 to 200PSI, and try to imagine it in reverse as an implosion, at 20 or 30 times more pressure. Kind of macabre to contemplate I guess but it is definitely a very unusual situation physics-wise.

Edited By Hopper on 23/06/2023 10:14:10

[Ady1Participant @ady1]

The unit would get bashed about on deck and when it was being moved about, not good for carbon fibre

I'm assuming that it never got close enough to get bashed about at depth but I think I read they got stuck at one point so there could be at-depth collision risks too

edit: I've only seen carbon fibre fail once and it explodes catastrophically so it would have been quick

Edited By Ady1 on 23/06/2023 10:15:10

[HopperParticipant @hopper]

Posted by Ady1 on 23/06/2023 10:12:10:

The unit would get bashed about on deck and when it was being moved about, not good for carbon fibre

I'm assuming that it never got close enough to get bashed about at depth but I think I read they got stuck at one point so there could be at-depth collision risks too

Yes. One report quoting someone in the "deep submersible community" said the inside word was the vessel was at about 3500 metres when all went quiet, so any existing damage would be critical at that level.

I was involved in tech documentation for submarines under construction years ago. They had a very large, very thick carbon fibre major component that was not part of the main pressure vessel, but specs were any scratches deeper than 1mm required replacement. (At cost of over half a million dollars back in the 1990s.) Anything less could be polished out. I imagine the Titan's main pressure vessel in this case would be even more critical because submarines do not go down to anywhere near Titanic depths, not even close.

Edited By Hopper on 23/06/2023 10:24:58

[Michael GilliganParticipant @michaelgilligan61133]

This is linked in the discussion that I mentioned earlier

[i.e. the edit of my first post on this page]

Trivially low differential pressure …but look what it does !

.

.

MichaelG.

[HopperParticipant @hopper]

Whoa. That was quick. And only 14 PSI or so pressure on that shell. Trying to comprehend 6,000PSI in the same situation is almost impossible, I find.

[Ady1Participant @ady1]

Posted by Hopper on 23/06/2023 09:54:06:

I would be a bit suspicious of the area where the carbon fibre cylinder joins the two titanium end domes. Seems like the variation in the way the two materials behave under repeated compression/decompression cycles could become an issue over time. The sub had made at least a dozen previous dives to the Titanic so it may be something that only showed up after repeated cycling, as often happens.

I would agree with that

once you take the massive pressures involved into account the dissimilarity of different materials becomes a major factor

The aircraft industry has big issues with far lower pressures

edit:The dissimilar hull sections would probably make it impossible to certify by LLoyds etc

Edited By Ady1 on 23/06/2023 10:41:44

[Dave HalfordParticipant @davehalford22513]

I did the crushing can experiment in a 60's physics class, waiting for the water vapour to cool and condense made for a slow distruction of the can.

[CirclipParticipant @circlip]

Yep, the crushed tin can as a Physics experiment in skools sixty odd years ago. Sympathy to the families, why? the participants didn't think of this when signing their lives away on their jaunt.

After a family day on board one of the Navy's tin tubes part of which was underwater, I initially had trouble coming to terms with the inevitability of the results of something going wrong with the boats my partners two Sons were crew on, especially given the 'Games' involving another nation in particular and the fact that we wouldn't get to know the full facts of demise due to an 'Incident'. Her attitude was that in this event, THEY were doing what they wanted to do.

At least they were part of a professional 'Company' for whom the last catastrophic accident occurred more than sixty years ago.

Regards Ian.

[Robert Atkinson 2Participant @robertatkinson2]

CFRP is not very ductile. As a teenager I intentionally impolded old, non implosion protected TV cathode ray tubes. Even at just 15PSI differential the energy involved left a lasting impresion (mental not physical, I took precutions) on me.
From images on the company website the center body construction seemed to be a metallic tube former with end flanges wound with carbon fiber tape. The tape was presumably pre-preg. There may have been details left out or even misrepresented to protect their trade secrets. However this does not appear to be an optimal design solution for withstanding external pressure. The CFRP is in compression, not the best use of it's properties. It is also unclear how forces are transfered from the CFRP to the flanges and thus end bells.

[Michael GilliganParticipant @michaelgilligan61133]

 

Here is my note about catastrophic failure of composites:

As mentioned earlier, we had a substantial Altitude Test Chamber … This was used both for testing our own products, and for hire to others. We had an enquiry from someone wanting an ‘Explosive Decompression Test’ on some fairly small equipment: this is to simulate the loss of a window or door on an aircraft.

 

Meanwhile, I was having some considerable success using Ciba-Geigy ‘F-Board’ for lightweight vibration test fixtures. This material has an aluminium honeycomb core with two thin skins of Glass Reinforced Epoxy [a high-tech equivalent of the construction used for internal domestic doors, etc.]

 

So … we hatched a plan:

1. Build a box from F-Board, with a pipe and valve connecting to the big chamber.
2. Seal the test item inside the box
3. Pull the big chamber to 30,000 feet
4. Open the valve

Sounds easy … but we felt obliged to first do a test on the F-Board.

The 3’ diameter hatch on the chamber had a nice wide flange, so it was a simple matter to attach a sheet of 2” board with a gasket of Plasticine.

Three of us were working late on another trial, so we had time to do this little test as a freebie.

 

I will mention here that there was a ‘closed porch’ built onto the chamber, to allow access through the hatch without losing too much heat or cold … This was timber framed, insulated with cork, about 3” thick, and double-skinned with hardboard.

 

We pulled the chamber to 10,000’ and held it for a while … everything was stable with no sign of leakage. So we proceeded.

As we approached 30,000’ there was an almighty bang and a rush of wind past our heads [the control panel was several feet away from the chamber, in an alcove]

 

Turning the corner … we realised that most of the ‘porch’ was missing, including its full-sized door !!

The F-Board had suffered ‘catastrophic failure’ and the inrush of air was sufficient to drag it all into the chamber.

 

My meeting next day, with the head of Test-House, was interesting … he was surprisingly supportive, despite the fact that the clean-up would involve overhaul of both vacuum pumps [it ended-up taking months].

 

There is a PostScript about Health&Safety Inspectorate, but I will save that for another day.

MichaelG.

Edited By Michael Gilligan on 23/06/2023 11:52:34

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 23/06/2023 09:17:28:

I share the scepticism that carbon fibre is a good choice…

I hope enough of the wreck is recovered to find out what went wrong, otherwise we'll soon be into conspiracy theories and red-herrings!

As to the technical cause, my guess is failure at a joint. The submersible seems to have consisted of a carbon-fibre cylinder sealed at both ends by Titanium domes. One the domes was fitted with an Acrylic Window, which maybe doubled as a hatch, possibly the other end was fitted with a hatch, or maybe an entire dome had to be taken off to get inside. However it was assembled, there are a number of risky joints. My chief suspect are the joints between the carbon-fibre body and the Titanium ends, closely followed by the Acrylic Window. Under pressure, Acryllc, Titanium and Carbon-fibre flex differently, and I expect the design included O-rings or similar to take up the slack. O-rings are pretty good, but…

If one trusts news reports, ahem, the owners appear to have deliberately exploited operating in international waters as a way of avoiding regulations and keeping costs down. (I've no problem with that sort of experiment unless they take paying passengers, or involve bystanders.)

We may never find out exactly what went wrong. As the firm were operating outside any national jurisdiction, I don't know who will organise and pay for the enquiry. which – done properly – will be expensive. There will be something, but may be skimped.

If there is an enquiry, I'd expect it to identify an accident chain, that is a series of decisions, possibly none critical in themselves, that combine to cause a disaster. It is ensuring accident chains cannot form that make H&S so tedious – common sense is hopeless at detail.

I'm guessing but, the Titan chain might go like this:

• An individual sees an opportunity to make money by offering affordable trips to see the Titanic. Big personal commitment to an interesting and exciting project, so maybe 'my baby' resulted in a 'can-do' mindset that ignored awkward concerns. Such chaps often surround themselves with 'yes-men'.
• Costs have to be kept low, forcing the need for:
  • a simplified vessel, forgetting that value engineering is the most difficult type of engineering in the world.
  • an avant-garde design using novel materials operating near the edge, that are difficult to inspect, with limited experience of their behaviour in an unusual environment .
  • minimised bureaucracy, maybe by evading the normal checks and rules.
  • maximum use of off-the-shelf components, which function with ordinary reliability. (Not daft, but their suitability in a special case needs careful evaluation)
  • relying on a small number of talented optimists to do the design with limited facilities rather than the large well-equipped and informed teams who normally develop high-tech vessels, whose work is Quality Assured.
  • deploying and recovering the vessel with simple methods that risk damaging it in small ways. Easy to forget that a trivial bump on the surface might become a horrendous stress raiser at 5500psi.
  • Fail to employ competent operators and maintenance staff.
  • Minimise maintenance and delay repairs
• Historically, there have been many examples of engineers under-estimating fatigue. Doesn't seem likely that parts made with a x10 safety factor will fail in normal operation due to mild flexing, yet it happens. Pessimists worry about fatigue, optimists assume hefty lumps will be fine!
• Even with costs trimmed to bone, building and operating a submersible is expensive, so it's probably been financed by loans requiring regular interest payments. Horrible things happen to the company and owner if the money isn't sorted, and the urgent need for assets to make a profit often encourages businesses to take unwise risks. Such as taking passengers before the vessel has been adequately tested.

Add all that together, and the risk of an adventurous enterprise going wrong is high, unless serious effort is put into de-risking the project throughout. I wonder if Oceangate did a risk assessment, and if so, what it says. I've worked on projects were management gambled high-risk/high-impact events wouldn't happen, and we often got away with it. In the face of instant pain it's very tempting to take risks for emotional reasons: people gamble all the time. In my world the risks were financial, but I've often wondered how a safety risk would have been managed – I'm certain some of my colleagues would have tolerated fatalities.

Bottom line is, if you take a risk, there's always a chance it will go wrong, and it pays to manage the possibility. Very little in life is completely safe, and we have to put up with it.

Dave

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