Titanic submersible

Well, The Lloyds Register requirement for a pressure hull for manned occupation (i.e. a manned submersible hull) MUST be designed with a Safety factor of FIVE. By contrast, an un-manned hull only requires to be designed with a SF of THREE. Fully certified and tested submersible hulls are therefore immensely strong. Different design SF are applied to other classes of marine equipment

Edited By mike T on 23/06/2023 23:39:26

Duncan

The entrance into the submersible was via the titanium end cover which had the acrylic window embedded in it, the titanium end cover, as far as I can see, was about the same diameter as the carbon fibre body of the submersible and was bolted to it, that is the way in by the whole titanium end cover which was then bolted into position. Dave W

Well, Rush paid for his cavalier approach that seems emerging, with his life - but he took four others with him.

I am surprised he even came out with statements about using sounds from the stressed components as warning signals. Whowever conducts the enquiry and how, given the complexity, it will no doubt elicit a lot of failures.

Designing manually-operated deep-water submersibles is not in in its infancy, and nor is materials science. This was not some pioneering project, but two aspects that made Titan differ from tried and tested vehicles were its cylindrical rather than spherical accommodation (to take more passengers) and of inhomogenous construction.

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The reference to early, manned space flights someone made further back misses the point that that was all still new engineering, but NASA did approach it properly. Also the pressure-hull comparison is wrong. A spacecraft has to hold a pressure of only 1 Bar, yes; but internally. A submersible or a submarine has to withstand 1 bar for every 10 metres depth, and externally. That difference in direction of load alone is crucial, even before you think of the pressure itself.

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Buffer reminds us of the desperately overloaded fishing-boat sinking with all those migrants in the Mediterranean.

They have not been forgotten despite all the reporting surrounding the Titan's loss; and what we are beginning to learn about how abominably the traffickers treated their passengers, is adding even more to the horror.

I heard, but not properly, an interviewee on the radio this evening apparently asking of the possibility of recovering the vessel and the bodies. Sadly this may not be possible. I don't know in which region of it the boat sank, but much of the Mediterranean is generally over 2500m deep. My atlas gives a spot depth of 3065m in the Ionian, South of the "heel" of Italy.

Pic of how the whole end dome swings aside for access. Carbon fibre hull is 5" thick. Acrylic window 21" diameter. There are various hull penetrations for control wiring between thrusters and controller, cameras, sensors, hydraulics to manually release ballast, externally mounted air scrubber system etc. All of which could also be weak points/stress points in repeated compression cycles.

Edited By Hopper on 24/06/2023 00:48:54

Edited By Hopper on 24/06/2023 00:50:05

Edited By Hopper on 24/06/2023 00:51:59

Edited By Hopper on 24/06/2023 00:53:44

I gather from others that Titan was an experimental craft engaged in scientific experiment and research, and so the passengers were not passengers but marine specialists or some other title and therefore part of the crew.

That sounds to me like a very dodgy legal device to avoid regulation and much else besides. Apparently there is a loophole in USA law over all this.

As Polar Star was based and went from Canada, and unless I am mistaken Canada is still a Dominion of the UK, and had 3 UK nationals on board it then Titan, we are probably going to have quite a contentious Inquiry procedure about this, same as happened in 1912.

It is my view that whatever device was used, this was a contract with a substantial payment for a trip on a ship then a submersible. And for those UK citizens, you cannot have a valid waiver or disclaimer of death for civilians. Such a waiver or disclaimer would be null and void.

Edited By julian atkins on 24/06/2023 01:37:23

Edited By julian atkins on 24/06/2023 01:38:30

Yes the lawyers' picnic has already begun. THIS legal expert says the waivers will not be valid in many cases where due precaution has not been taken. But THIS legal expert says OceanGate has options for court protection. Either way, the process will be long and costly to sort it out.

Then there is the matter of possible criminal charges HERE , a separate issue from any civil liability cases.

A lot will depend on the outcome of the upcoming investigation/s. Both Canada and US are launching investigations which presumably will work together.

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Not entirely ‘dodgy’ or a ‘loophole’ Julian … it is a necessary legal device employed by laboratories and test-houses worldwide to avoid certification and Health&Safety issues. I think the significant difference is that the management system in such places is required to be robust, and to to provide reasonable levels of safety.

[ the word ‘reasonable’ is enshrined in UK Law, and presumably elsewhere ]

In the unique set of circumstances surrounding this Titan voyage … the degree to which it can be considered ‘experimental’ as opposed to ‘tourist’ will, I am sure, keep the lawyers occupied for years to come.

MichaelG.

[ worked for 11 years in an accredited test-house ]

From the pic Hopper posted, it looks like the end cover was secured by a handful of m6 cap head bolts...!

It does doesn't it. However I guess they only need to hold it loosely in place for the first few dozen fathoms, after that they are surplus to requirements.

When the Titan was at the same depth as the Titanic, the pressure on the hull was supposedly around 6000psi. I assume then that with all that force on the outside of the hull, the inside must have shrunk a bit, increasing the pressure on the people inside the Titan. What does that increase do to the occupants? Can you feel it as the sub gets deeper? I know there is a problem with divers rising to the surface too quickly, the bends. So if the Titan had to surface quickly, was the main vessel equipped to handle "the bends"? If not, then the occupants would have been in serious danger after surfacing.

If the Titan wreckage is left on the sea bed, along with whatever is left of the occupants, would that sight deter others from visiting the Titanic?

Air pressure inside I think would be controlled at about 1 Bar. They have an external air scrubber module in the tail fairing to remove C02 and replenish oxygen as air is circulated through the system. So no danger to the passengers of the bends as the craft ascends. Bends comes from the body being subjected to rapidly varying pressure due to direct contact with the pressure of the water at depth.

But yes possibly some damage to the hull etc from too rapid expansion of the carbon fibre etc if they ascend too quickly. Hard to say for sure.

I don't think there will be much wreckage to view. Several deep see expert types seem to be saying that in a catastrophic implosion, everything not made of metal would be reduced instantly to dust. So the two titanium end domes and the rails and tanks the hull sat on plus a few bits and pieces such as air tanks and electric motors and pipework and wiring would be metal and may be lying about.

Sadly, the history of submersibles contains may cases of fatalities.

Some from human error (ranging from inadequate design / testing to the careless ) and to dedliberate, as in warfare.

We should all learn from mistakes, but with safety critical matters the care exercised needs to be extreme.

In this case, the environment entered, and the dangers involved have to be on a par with space exploration, where the boundaries of knowldge are reached, or surpassed.

They were indeed explorers

Howard

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Yes tiny. But the large hinge and latch would be the main location and then the bolts are only there to hold it in place until the water pressure squeezes the dome onto the hull. Looks like it must have a seal or o-ring in the dome flange surface to seal against that flat flange surface. Morton Thiokol all over again?

In some ways, more dangerous than space exploration, due to the extreme pressure differential. Only 1 Bar in a spacecraft. Almost 400 Bar pushing in on this craft. Bit like going into space sittiing on a fully charged steam boiler, only more so.

Explorers? I reckon there will be much discussion of that as the enquiry progresses. What was down there was already well known, observed and documented and not much new left to be discovered. And robots can do the job just as well.

Tourists? There is certainly an element of that. As with all tourism, there is a large element of seeking stimulation in an already over-stimulated world. In psychology they call it Optimum Stimulation Theory. Different levels for different folks. For some it might be seeing the Eiffel Tower.. For others its seeing the Titanic. For Branson and his mates it seems to be getting into space.

But I am sure this tragedy will bring as much change to the submersible industry as Titanic did to the shipping industry in 1912. I would be surprised if we see another carbon fibre submersible. But it depends on what the inquiry finds. Could have been something else that failed. Time will hopefully tell.

My understanding (such as it is!) of a carbon fibre hull implosion is that it'd be an everywhere-all-at-once event with very large numbers of fractures developing practically simultaneously - hence no description of finding the hull or large fragments of it.

An O-ring seal failure would have an equally fatal, though rather different outcome wouldn't it?

Yes you would think so. Equally deadly to human life but not such a catastrophic implosion perhaps, you would think.

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+1 … which is why I was so dubious about the acoustic monitoring system

If it detects any sound, it’s already too late … I would posit.

MichaelG.

This, from 2020 took some finding: **LINK**

https://www.jeccomposites.com/news/oceangate-selects-toray-as-provider-of-prepreg-carbon-fiber-for-deep-sea-submersible-hull/

Not sure if it tells us much, but I offer it for consideration

MichaelG.

On the point about hull compression raising the internal air pressure, the normal volume change hence air-pressure rise by shell compression should be minute, provided the material's movement is within its elastic limit.

It it is not, the shell is collapsing anyway.

I don't know how long an emergency ascent from 3000m would take but even then the consequent reduction to ambient air pressure will be as small as its increase was, and relatively slow. So I would not think "the bends" any likely hazard.

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The Bends cited by Hopper, or Decompression-sickness, was originally called "Caisson Disease" as it was first identified among civil-engineering labourers working in sub-estuarine caissons for building bridge piers*. It is not directly an an effect of water at high-pressure on the body.

Instead it is an effect of breathing compressed-air at pressures equivalent to ambient even at quite modest pressures, depending on time. The bridge-builders were working hard, surrounded by high-pressure air, for some hours at a time.

In these conditions the blood absorbs nitrogen, and if the pressure is released too rapidly it cannot come out of solution in a gentle manner, but effervesces slightly, creating bubbles that typically lodge in the joints, causing great pain.

Treatment is by putting the patient in a decompression-chamber in which the air pressure is raised to the diving depth then released at a very slow, controlled rate over as many hours as calculated for the case.

SCUBA Divers usually stay within fairly shallow depths but if venturing deeper, especially to 30+m with some time at depth, take enormous care over gas-mixtures, the potentially toxic or narcotic effects of atmospheric gases at high pressure, times at depth, ascent decompression-stops, short decompression-oxygen breathing, etc. Even then things can go wrong. The complications are multiplied greatly if the dive profile (depth, distance and time) is not a single dive to a steady depth but rises and falls like a switchback, even alternating from open air to considerable depths a few times - but this is normally only met in cave-diving, not the sea.

So air-pressure change by a submarine's hull compression is not going to lead to The Bends. I would expect the shell to contract slightly, but if enough to raise the internal pressure significantly, it is passing beyond its elastic limit....

... and that is a design consideration. As are the mind-bogglingly complicated stress and strain calculations for external pressures on a shell that although basically cylindrical, is not of single material and contains shape-changers like interpenetrations and mountings.

I have seen a video of a plain cylinder collapsing, in a hydrostatic test-tank. It was a fairly small container intended for marine electronic equipment, but failed well within its intended working-pressure for some reason, while undergoing the test as specified. It gave no visible warning such as slow buckling, but ruptured suddenly and implosively.

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*I believe the first cases questioned, against considerable medical and commercial opposition, were among the men building the Brooklyn Bridge, in New York.

I can't imagine OceanGate has a huge amount of money to pay out, if found guilty.

I wonder if OceanGate managed (somehow) to convince an insurance company to give them cover.

If so, then the lawyers will target the insurance company, but insurance companies are well versed at repelling boarders.

Ches