Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Titanic tourist submersible goes missing with search under way

bbc.com

Post reply on HN
Print view View original

111–120 of 649 posts

Re: Titanic tourist submersible goes missing with search under way

#111

Post by carbine »

I'm hesitant to speculate but just sharing -- an earlier version of this submersible was scrapped:

"OceanGate will take advantage of lessons learned during the construction of its carbon-hulled Titan submersible, which was originally built for Titanic journeys. Rush said tests that were conducted at the Deep Ocean Test Facility in Annapolis, Md., revealed that the Titan’s hull “showed signs of cyclic fatigue.” As a result, the hull’s depth rating was reduced to 3,000 meters.

“Not enough to get to the Titanic,” Rush said."

Source: https://www.geekwire.com/2020/oceangate-raises-18m-build-big...

Re: Titanic tourist submersible goes missing with search under way

#112

Post by Yeroc »

MallocVoidstar wrote: post #103
MiguelX413 wrote: post #102

Why do they keep emphasizing the fact that the submarine has gone missing and not the people within it?

As far as I can tell I think the company involved hasn't released a passenger list. edit: An earlier version of the BBC's article said it wasn't known if people were on it at all; clearly there were, but I'd bet this is why the headline is so unclear.

Sky News https://news.sky.com/story/uk-billionaire-hamish-harding-on-...> identifies several of the passengers including:

- Hamish Harding

- Paul-Henry Nargeolet

- Stockton Rush (the President and CEO of OceanGate itself)

Re: Titanic tourist submersible goes missing with search under way

#113

Post by floxy »

stickfigure wrote: post #105
floxy wrote: post #95

Earlier quoted context omitted.

Here is an article with a few more details on the construction of the Cyclops vessel: https://www.compositesworld.com/articles/composite-submersib... ...still not seeing what the carbon fiber is buying here, other than historical reasons / "that's how we do composite pressure vessels". Maybe it adds some slight rigidity when it is being raised up out of the water?

I would guess weight? From pictures, the launch platform doesn't look like something that could manage a tube fabricated from 5" thick steel.

It seems like the epoxy in this composite structure is sustaining all of the compressive loads. The carbon fiber would seem to be just along for the ride, so to speak, since fibers are only useful in tension. Am I missing something?

Re: Titanic tourist submersible goes missing with search under way

#114

Post by CarVac »

floxy wrote: post #95
pge wrote: post #82

Earlier quoted context omitted.

The CBS news article referenced in another reply says the body of the sub is 5-inch thick carbon fiber with titanium used in the rounded ends. I am surprised it’s just carbon fiber in the body.

Here is an article with a few more details on the construction of the Cyclops vessel: https://www.compositesworld.com/articles/composite-submersib... ...still not seeing what the carbon fiber is buying here, other than historical reasons / "that's how we do composite pressure vessels". Maybe it adds some slight rigidity when it is being raised up out of the water?

Carbon fiber is used because it is rigid.

The failure mode for a member in compression is buckling, which is resisted by stiffness, not strength.

It's also a lot easier to make a huge thick tube out of composites than out of titanium. That's why only the spherical ends are titanium, and the middle tube part is CF.

Re: Titanic tourist submersible goes missing with search under way

#115

Post by krisoft »

readams wrote: post #68
kortex wrote: post #47

Earlier quoted context omitted.

I'm not really an engineer (general hobbyist, former chemist) but I have built and worked with pressure and vacuum vessels. Positive pressure (tank vs exterior) is much easier to deal with than negative pressure (vacuum vessel at 1 atm, or bathyscape with 1 atm inside and high pressure exterior). In positive pressure, your stress is mostly in the hoop mode, which is stable. This is why aluminum cans can be so thin. I…

Also space pressure difference is much less. A fuel tank might have just a few atmospheres inside, and of course a human pressure vessel will have a bit under 1 atmosphere inside, compared to the outside which is at ~0 atm. At 4000m, the outside pressure is _400_ atmospheres compared to just one inside. It's way, way harder.

> A fuel tank might have just a few atmospheres inside

Not quite. The composite overwrapped pressure vessels (COPV) we are talking about are easily pressurised up to 5000 psi [1]. That is about 340 atm. They use these tanks to contain helium as a pressurant, and nitrogen for the life support systems.

Elon talked in a tweet about higher numbers. 6k psi and 10k psi in this tweet[2] but it is unclear if he is talking about design works or actual pressures they have flown.

All in all you are right that the difference between the people tank and space is only 1 atm, but that is not where the challenge is in terms of space exploration and pressure vessels.

1: https://ntrs.nasa.gov/api/citations/20110015972/downloads/20...

2: https://twitter.com/elonmusk/status/1501673373813907464

Re: Titanic tourist submersible goes missing with search under way

#116

Post by HWR_14 »

rwmj wrote: post #62
ralphhughes wrote: post #40

Skimming the website, I assume this submersible is using electromagnetically attached drop-weights so that if anything goes wrong and power is lost, the weights drop off and the submersible floats up to the surface again? And 96 hours of life support sounds good, but unless there is another submersible nearby that can dive down, find them AND attach a line, the number of hours of life support will be irrelevant. Of c…

Wouldn't the sub have a tether to the surface, or is that not practical for some reason?

Leaving aside the literal tons of weight a tether would require just to life a single person back to the surface (and the weight of the tether), it also could get pushed around a lot by the current. And, most importantly, once you are down there and want to navigate the wreck it would get in the way.

Re: Titanic tourist submersible goes missing with search under way

#118

Post by ocdtrekkie »

breck wrote: post #43
comrh wrote: post #42

Earlier quoted context omitted.

I was curious too. > Contacted by CBS News, the Canadian Coast Guard said the rescue operation was being managed by the Boston Regional Coordination Center, and a map showing jurisdictions for the various coastal search and rescue agencies off the North American coast shows the location of the Titanic wreck within the Boston center's area of responsibility. https://www.cbsnews.com/news/titanic-submarine-missing-rescu…

I always assumed the Titanic went down further north. Didn't know there were icebergs that far south. Edit: they float there https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/wea.2...

The Titanic didn't know there were icebergs that far south either.

Re: Titanic tourist submersible goes missing with search under way

#119

Post by lb1lf »

daveslash wrote: post #20
beowulfey wrote: post #2

Not a lot of information about this one. Does the Coast Guard have a submersible of their own that they could use to recover, even if they were able to find them?

Yeah, the article is light on details. We don't know if they sank or if they're adrift on the surface somewhere after some failure. If they experienced an emergency underwater and were not able to surface, I'd fear for the absolute worst. People can survive in sunken submarines long enough to be rescued, but those are typically large submarines with multiple rooms that they can seal themselves off in. I doubt a touri…

If the sub was designed like a few other deep-sea craft I've looked at, they'd have positive buoyancy and weights to overcome this; the idea being that having to blow ballast tanks at 400 bar pressure differential is rather inconvenient and failure prone.

Instead, the weights (attached with electromagnets) are simply jettisoned when it is time to recover to the surface and off you go. The upside to such a simple system, of course, is that it is exceedingly reliable and fail safe.

Provided you do not suffer a hull implosion, of course.

Re: Titanic tourist submersible goes missing with search under way

#120

Post by sclarisse »

ghaff wrote: post #73
echelon wrote: post #58

Earlier quoted context omitted.

I don't think it's stupid to expect that submersibles are well-engineered. I'd also imagine that the tourists trusted the reputation of the operator. Both the state of the equipment and that their safety checks and processes were stringent. Especially since they claimed to aid in the science. There aren't many priors for civilian submarine disasters.

I'm not sure there's any particular reason to think that this is an extraordinarily dangerous activity relative to things like mountain climbing--even on many less extreme peaks.

The particular reason is “450 atmospheres of water pressure.” This is a lot. You don’t have this type of threat to the structural integrity of your gear at Everest, etc.
Post reply on HN