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.
Pressure hull made from titanium and carbon fiber, capable of diving to 4000m (13,000 ft).
I recall that one reason SpaceX switched from carbon fiber to stainless steel pressure vessels (fuel tanks) was the difficulty of detecting structural flaws.
Can any engineers comment on whether that task is easier for a vessel exposed to compression (under sea) as opposed to vacuum (space)?
How likely is a catastropic failure due to undetected flaws in carbon or composite (carbon + Ti) structures like these?
I've had some work in designing vessels to take external pressure.
It's fundamentally a nonlinear problem. A lot of new(and some not so new) engineers don't understand the process of solving it properly
For instance, euler buckling is the simple eigenvalue problem of solving a column in compression. But, it misses: initial defect because nothing is truly straight, material nonlinear effects if the part approaches yield strength, etc. I've seen it overestimate compressive capacity as much as 3-10 times depending on how geometry and material. You have to use more advanced techniques than just force over area.
Metallic vessels are difficult enough. You have to set up the problem properly and run nonlinear solves in the right way, and account for the right (or at least bound it conservatively) initial imperfections and analyze. And provide margin. Lots of compute time for a realistic analysis. And you probably still want to test. And you want to know your material very well, as the higher it's loaded, the more nonlinear that behavior could be too.
And that's with the simplicity of metal.
Composites are different. And that's not accounting for complexities of this problem. A lot of things get brittle at lower temperatures. Steel does, and I'm not sure about this particular material but at depth I would want to know specifics of temperatures and material behavior and select the right material for the job. Matrix and fibers themselves. Either failing would be fatal. I don't know enough here to say anything other than there are a lot of variables and I'm far enough away from the problem that it would take a lot of data to convince myself that I understood what could possibly happen.
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. In negative pressure vessels, you have a buckling mode, which is inherently unstable. As soon as it goes, it goes all at once.
I've had a 2L glass vacuum flask implode on me. There is no warning. All it takes is a tiny defect, and once you hit a certain pressure delta, kaboom. Composite is similar in that it's mostly brittle failure vs ductile. I've also imploded a 55 gallon steel vessel. That goes a lot more gradually (though still fast) - maybe enough to detect and abort the trip.
The other main advantage of steel vs composite is you can inspect with X-ray imaging to find defects.
Carbon fibers are strong in tension. That's why it is good for pressure vessels that are trying explode. Your wrap the fibers on the outside of the pressure boundary. Same concept that you can only pull on a rope, not push it. I'd be interested to see how they are using carbon fibers in compressive applications like deep sea vessels. Is that more of a marketing thing? "Carbon fiber" sounds sexy, so we'll advertise that we're using it, but it is really for non-load bearing applications?
>The most significant innovation is the proprietary real-time hull health monitoring (RTM) system. [...] provides early warning detection for the pilot with enough time to arrest the descent and safely return to surface.
I imagine the search and rescue effort have checked the seismograph/ocean sounds/other networks, AIUI an implosion at depth makes quite a bang, so not detecting one would be a positive.
There's a formula for designing the strain on pressurized vessels especially when the
strength characteristics of the material used is known
The thicker the material used for the vessel the more pressure It will take That's obvious & simple so far
They used carbon fiber and titanium fiber probably interwoven and then glued there is a procedure for this
There's also a nominal, working, and burst value after these vessels are manufactured. Basically established by testing
There was no testing on this vehicle non-destructive or destructive That was bypassed
Also I believed it was planned to be a 7-in thick vessel this one for some reason was 5-in thick
Two of the employees from oceangate were sued and dismissed for making issues of the safety of this vessel particularly about the thickness and particularly about the gluing process
(That isn't even that strange in any industry where there is engineers)
Especially in R&D situation like this
So you have a material which the mechanics of that material are not fully understood
Being used to manufacture a vessel that's going to withstand unimaginable pressures because of its size every square inch of that vehicle had 4,000 per square inch on it
It's of a certain configuration (shape)
Needs to be tested
The other thing I would bring up is I wonder if the gasket failed they're almost at full depth
Maybe they didn't change the gasket or they change the gasket and it was of a different physical characteristics
The gasket is used on the hatch which was bolted shut
The gasket surface design is very critical at that pressure also
I think you can rule out fatigue because carbon fiber and titanium for that matter have really high fatigue resistance
My background is in aerospace and while I’m not an expert on COPVs, I’m familiar with their design. Carbon fiber overwrap is really good for internal pressure applications or in other words, the typical pressure vessel due to carbon fiber’s very high tensile strength. Think of those videos where folks put rubber bands on watermelons to make them explode; the concept is similar to a COPV in that the rubber bands (carbon fiber) “compress” the watermelon (pressure vessel) to “contain” the pressure. COPVs can take high internal pressures of 6000 PSI (which is the same internal pressure of the ISS NORS tank used to recharge oxygen and nitrogen on the ISS and coincidentally is the same *external* pressure experienced at the depths of the Titanic. (Some helium bottles have higher internal pressure). While in aerospace applications there are some load cases where the COPV has an external pressure load on them like a helium bottle stored in a propellant tank on a SpaceX Falcon 9, those pressures are nowhere near deep sea pressures.
The reason why I don’t think COPVs are a good design for an external pressure application is the load direction; carbon fiber tow doesn’t really do well maintaining an external load. Think back to the watermelon example; apply an increased external pressure and the rubber bands really don’t help with withstanding that increased pressure.
Carbon fiber itself is very difficult to verify that you have the correct properties once they're wound onto the tank. The properties are anisotropic meaning depending on the direction of the fiber you’re gonna get different mechanical properties. Defects like delamination (when a wind unwraps) or voids between the tank wall and fiber are common if you don’t have a qualified winding operation and really really good procedures. In short, while not needing software, repeatability in manufacturing a COPV is incredibly difficult. Part of the reason SpaceX switched to metal tanks is that the mechanical properties of stainless actually increase in a cryogenic environment so there’s an added benefit.
In 2016, SpaceX’s Falcon 9 carrying AMOS-6 exploded during a routine static fire due to a buckled liner of a COPV on the 2nd stage LOX tank. The liner buckled which created a void between the liner and the fiber overwrap which then developed solid oxygen (or an ingress of LOX) that initiated an explosion due to friction. Falcon 9 had been flying for 6 years at that point so I’d consider that a pretty mature or at least an “operational” vehicle so for it to explode on the pad like that is how tricky COPVs can be.
I think Titan imploded killing the crews instantly. This would explain sudden lost of contact and subsequently unable to find them. Those fiber has been confirmed to buckle from cyclic pressure. The take away from this incident is OceanGate should have pursue Edison manual ways of repetitive testing. It would be very expensive but the knowledge gather from those test will enhance material science of carbon fiber use in that kind of scenrios and design specs. Instead they prefer to fire the engineer whistleblower who try to save them. Such irony.
For those looking for more detail on the engineering of the vessel, refer to this brief walk-through from Rush himself filmed by a Mexican travel blogger back in July of 2021:
The failure of the carbon fiber is a repeated theory of what could have happened to OceanGate Titan. Is there any information on the difference expansion and contraction of titanium versus carbon fiber. The seal between the end-caps and the carbon fiber hull would have to be very flexible and would be susceptible to failure. Any thoughts on the seals being the failure? I'm a US submarine veteran.
I wonder if it has an adaptive pressurisation system, similar to airplanes but in the opposite direction, where the internal pressure is allowed to increase up to a certain point as it descends to reduce the pressure differential.
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 course if the pressure hull has failed catastrophically it will have been over mercifully quickly. Anyone know if deep-diving submersibles are required to carry black-boxes like aircraft?
A location pinger would be a no brainer but like you say, it only helps if there's another sub with a grapple in range, in time.
I understand why oceanographers /might/ want to do this, but not in person when ROV tech is so good now, for biology and tourism. There are so many things that can happen to fragile humans in that complex machine: drowning, freezing, asphyxiating, crushing, oxygen narcosis, nitrogen narcosis, co2 poisoning, and the plain old bends.
So why do people risk all that, and pay 125k to do it? Why the titanic obsession? It's only the fourth worst maritime disaster (Doña Paz in 1987 had 4k deaths) and so what if someone made a movie about one.
> I assume this submersible is using electromagnetically attached drop-weights so that if anything goes wrong and power is lost
I don't think they have any "drop-weights" which would make them positively buoyant. If I'm reading the spec-sheet correctly, the submersible itself weights ~1500lbs. Subs have ballast tanks which they pump with air and force out water to make themselves positively buoyant. But if something goes wrong with the mechanism to fill the ballast tanks, I'm guessing they'd just be stuck at depth.
(disclaimer, I am far from an expert at this - I just have a cursory understanding of Boyle's law)
I've read that many military submarines have an "I've sunk" buoy. It detaches from the boat under commanded deployment, after some elapsed time without reset, or when external pressure rises way beyond crush depth. They're positively buoyant. They have radio beacons to report the event when they rise to the surface.
Some articles I found suggest that a trip was 8 hours to get there and back. Another mentioned being in the sub for 12 hours. I'm guessing it's a 4 hour trip each way and then they spend a number of hours checking the wreckage.
The wreckage site is around 370 miles from Newfoundland, Canada.
Seems like the rescue effort could be unfolding over days.
>David Concannon, an adviser to the company, said Oceangate lost contact with the sub Sunday morning. It had a 96-hour oxygen supply, he said in an email to The Associated Press on Monday afternoon. “Now 32 hours since sub left surface,” said Concannon, who said he was supposed to be on the dive but could not go due to another client matter. He said officials are working to get a remotely operated vehicle that can reach a depth of 6,000 meters (about 20,000 feet) to the site as soon as possible.
They went during a brief weather window. One of the people on board had suggested just prior to departing that this was likely to be the only trip the vessel made this season. Rough phrasing in hindsight.
For those mentioning about detailed location tracking / communication: Non-low-bandwidth communication underwater is really difficult due to the physics of EM waves traveling through a medium such as water: https://en.m.wikipedia.org/wiki/Underwater_acoustic_communic...
Exactly. Judging from that video their approach to designing and building that thing seeks very amateurish, nonchalant, and lacking an eye for redundancy and safety.
Not an expert...but my impression is that the implosion, at depth, of even the very small submarine in question here would generate an extremely loud "noise". Probably obvious to any hydrophone on the support vessel, and near-certainly recorded in detail by military monitoring systems.
"Real-Time Health Monitoring
The most significant innovation is the proprietary real-time hull health monitoring (RTM) system. Titan is the only manned submersible to employ an integrated real-time health monitoring system. Utilizing co-located acoustic sensors and strain gauges throughout the pressure boundary, the RTM system makes it possible to analyze the effects of changing pressure on the vessel as the submersible dives deeper, and accurately assess the integrity of the structure. This onboard health analysis monitoring system provides early warning detection for the pilot with enough time to arrest the descent and safely return to surface."
I am surprised that real time monitoring of the hull is even a consideration, I would have expected it to be designed an built with massive safety margins and then inspected very thoroughly after each trip. The above paragraph seems to indicate that they would monitor hull health during the trip and stop descent if it showed signs of stress. But I am skeptical that they would see signs of stress before it simply imploded at depth.
It's worth contrasting the design of this vehicle with what is ostensibly the world standard for deep-sea research submersibles, Alvin of Woods Hole Oceanographic Institution.
They just had a story on this on CBS Sunday Morning. A reporter actually went down in the sub but it got called off mid-dive. He had to go back later. It didn't seem safe.
I'm surprised the craft doesn't have a pinger, like airplane black boxes do (and those can survive on the ocean floor, too). 96 hours of oxygen won't help if it takes 200 hours just to find where they are.
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?
I don't understand after all these years why there's still this obsession with the Titanic. What keeps fueling its enduring fascination? People spending 1/4 million just to barely see a sunken ship? Bragging rights for the rich?
It's intriguing to see what kind of personality a billionaire has that pushes him to do these stunts and also publicly brag about them. I hope it's not a necessary ingredient to success as I do not intend to live like that.
That being said,
> He added that because the passengers were sealed inside the vessel by bolts applied from the outside, "There's no way to escape, even if you rise to the surface by yourself. You cannot get out of the sub without a crew on the outside letting you out."
How come there's no way to communicate once under water? Wouldn't be possible to launch a tiny probe attached to the exterior of the sub, either manually or automatically when in trouble, sort of a black box, that bounces back to the surface to broadcast crew messages, sub data and location? Seems like an obvious safety device to have. Are there any technical reasons why this is not available on a vehicle with suck poor performance?
[+] [-] carbine|2 years ago|reply
"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...
[+] [-] scarnz|2 years ago|reply
https://oceangate.com/our-subs/titan-submersible.html
Pressure hull made from titanium and carbon fiber, capable of diving to 4000m (13,000 ft).
I recall that one reason SpaceX switched from carbon fiber to stainless steel pressure vessels (fuel tanks) was the difficulty of detecting structural flaws.
Can any engineers comment on whether that task is easier for a vessel exposed to compression (under sea) as opposed to vacuum (space)?
How likely is a catastropic failure due to undetected flaws in carbon or composite (carbon + Ti) structures like these?
[+] [-] mechhacker|2 years ago|reply
It's fundamentally a nonlinear problem. A lot of new(and some not so new) engineers don't understand the process of solving it properly
For instance, euler buckling is the simple eigenvalue problem of solving a column in compression. But, it misses: initial defect because nothing is truly straight, material nonlinear effects if the part approaches yield strength, etc. I've seen it overestimate compressive capacity as much as 3-10 times depending on how geometry and material. You have to use more advanced techniques than just force over area.
Metallic vessels are difficult enough. You have to set up the problem properly and run nonlinear solves in the right way, and account for the right (or at least bound it conservatively) initial imperfections and analyze. And provide margin. Lots of compute time for a realistic analysis. And you probably still want to test. And you want to know your material very well, as the higher it's loaded, the more nonlinear that behavior could be too.
And that's with the simplicity of metal.
Composites are different. And that's not accounting for complexities of this problem. A lot of things get brittle at lower temperatures. Steel does, and I'm not sure about this particular material but at depth I would want to know specifics of temperatures and material behavior and select the right material for the job. Matrix and fibers themselves. Either failing would be fatal. I don't know enough here to say anything other than there are a lot of variables and I'm far enough away from the problem that it would take a lot of data to convince myself that I understood what could possibly happen.
[+] [-] kortex|2 years ago|reply
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. In negative pressure vessels, you have a buckling mode, which is inherently unstable. As soon as it goes, it goes all at once.
I've had a 2L glass vacuum flask implode on me. There is no warning. All it takes is a tiny defect, and once you hit a certain pressure delta, kaboom. Composite is similar in that it's mostly brittle failure vs ductile. I've also imploded a 55 gallon steel vessel. That goes a lot more gradually (though still fast) - maybe enough to detect and abort the trip.
The other main advantage of steel vs composite is you can inspect with X-ray imaging to find defects.
[+] [-] engineer_22|2 years ago|reply
In space the main issue is containing internal pressure - so the skin is all in tension.
While a submersible the pressure is from without - so the skin is all in compression.
[+] [-] floxy|2 years ago|reply
[+] [-] moralestapia|2 years ago|reply
Interested to know more about what happened.
[+] [-] zh3|2 years ago|reply
[+] [-] foobar1962|2 years ago|reply
I believe the pressure where the Titanic lays is 300 atmospheres. The pressure differential for the submarine is 300 - 1 = 299 atmospheres.
A vessel in space will be have a pressure differential of 1 atmosphere to contend with.
[+] [-] skibsky|2 years ago|reply
The thicker the material used for the vessel the more pressure It will take That's obvious & simple so far
They used carbon fiber and titanium fiber probably interwoven and then glued there is a procedure for this
There's also a nominal, working, and burst value after these vessels are manufactured. Basically established by testing There was no testing on this vehicle non-destructive or destructive That was bypassed
Also I believed it was planned to be a 7-in thick vessel this one for some reason was 5-in thick
Two of the employees from oceangate were sued and dismissed for making issues of the safety of this vessel particularly about the thickness and particularly about the gluing process
(That isn't even that strange in any industry where there is engineers) Especially in R&D situation like this
So you have a material which the mechanics of that material are not fully understood
Being used to manufacture a vessel that's going to withstand unimaginable pressures because of its size every square inch of that vehicle had 4,000 per square inch on it
It's of a certain configuration (shape) Needs to be tested
The other thing I would bring up is I wonder if the gasket failed they're almost at full depth Maybe they didn't change the gasket or they change the gasket and it was of a different physical characteristics
The gasket is used on the hatch which was bolted shut The gasket surface design is very critical at that pressure also
I think you can rule out fatigue because carbon fiber and titanium for that matter have really high fatigue resistance
LJK
[+] [-] 32faction|2 years ago|reply
The reason why I don’t think COPVs are a good design for an external pressure application is the load direction; carbon fiber tow doesn’t really do well maintaining an external load. Think back to the watermelon example; apply an increased external pressure and the rubber bands really don’t help with withstanding that increased pressure.
Carbon fiber itself is very difficult to verify that you have the correct properties once they're wound onto the tank. The properties are anisotropic meaning depending on the direction of the fiber you’re gonna get different mechanical properties. Defects like delamination (when a wind unwraps) or voids between the tank wall and fiber are common if you don’t have a qualified winding operation and really really good procedures. In short, while not needing software, repeatability in manufacturing a COPV is incredibly difficult. Part of the reason SpaceX switched to metal tanks is that the mechanical properties of stainless actually increase in a cryogenic environment so there’s an added benefit.
In 2016, SpaceX’s Falcon 9 carrying AMOS-6 exploded during a routine static fire due to a buckled liner of a COPV on the 2nd stage LOX tank. The liner buckled which created a void between the liner and the fiber overwrap which then developed solid oxygen (or an ingress of LOX) that initiated an explosion due to friction. Falcon 9 had been flying for 6 years at that point so I’d consider that a pretty mature or at least an “operational” vehicle so for it to explode on the pad like that is how tricky COPVs can be.
EDIT: Spelling and clarification on delamination
[+] [-] oneTbrain23|2 years ago|reply
[+] [-] nickocrates|2 years ago|reply
(Skip to 18:05 for Rush's explanation of the sub) https://www.youtube.com/watch?v=uD5SUDFE6CA
[+] [-] carabiner|2 years ago|reply
[+] [-] bubblehead8780|2 years ago|reply
[+] [-] zabzonk|2 years ago|reply
titanic is at about 12500, according to wkikipedia - a bit close?
[+] [-] userbinator|2 years ago|reply
[+] [-] ralphhughes|2 years ago|reply
[+] [-] imglorp|2 years ago|reply
I understand why oceanographers /might/ want to do this, but not in person when ROV tech is so good now, for biology and tourism. There are so many things that can happen to fragile humans in that complex machine: drowning, freezing, asphyxiating, crushing, oxygen narcosis, nitrogen narcosis, co2 poisoning, and the plain old bends.
So why do people risk all that, and pay 125k to do it? Why the titanic obsession? It's only the fourth worst maritime disaster (Doña Paz in 1987 had 4k deaths) and so what if someone made a movie about one.
[+] [-] lode|2 years ago|reply
https://www.youtube.com/watch?v=29co_Hksk6o
"I couldn't help noticing how many pieces of the sub seemed... improvised."
[+] [-] spokeroni|2 years ago|reply
I don't think they have any "drop-weights" which would make them positively buoyant. If I'm reading the spec-sheet correctly, the submersible itself weights ~1500lbs. Subs have ballast tanks which they pump with air and force out water to make themselves positively buoyant. But if something goes wrong with the mechanism to fill the ballast tanks, I'm guessing they'd just be stuck at depth. (disclaimer, I am far from an expert at this - I just have a cursory understanding of Boyle's law)
edit: upon viewing this video https://www.youtube.com/watch?v=29co_Hksk6o&t=157s they seem to have construction pipes as ballasts that they can drop :| God help the poor souls on that sub
[+] [-] ridgeguy|2 years ago|reply
edit: No cites, sorry.
[+] [-] gexla|2 years ago|reply
The wreckage site is around 370 miles from Newfoundland, Canada.
Seems like the rescue effort could be unfolding over days.
[+] [-] rwmj|2 years ago|reply
[+] [-] Mistletoe|2 years ago|reply
It’s bolted from the outside.
[+] [-] spoonfeeder006|2 years ago|reply
If so how do you know that?
[+] [-] jiveturkey|2 years ago|reply
mercifully quickly?
[+] [-] unknown|2 years ago|reply
[deleted]
[+] [-] dangle1|2 years ago|reply
>David Concannon, an adviser to the company, said Oceangate lost contact with the sub Sunday morning. It had a 96-hour oxygen supply, he said in an email to The Associated Press on Monday afternoon. “Now 32 hours since sub left surface,” said Concannon, who said he was supposed to be on the dive but could not go due to another client matter. He said officials are working to get a remotely operated vehicle that can reach a depth of 6,000 meters (about 20,000 feet) to the site as soon as possible.
https://www.seattletimes.com/nation-world/nation/a-search-is...
[+] [-] prawn|2 years ago|reply
[+] [-] jacooper|2 years ago|reply
[+] [-] rajnathani|2 years ago|reply
[+] [-] Animats|2 years ago|reply
[1] https://twitter.com/FnpMarieOH/status/1670931677013524487
[+] [-] tim333|2 years ago|reply
[+] [-] AdamN|2 years ago|reply
[+] [-] iancmceachern|2 years ago|reply
[+] [-] bell-cot|2 years ago|reply
[+] [-] ciguy|2 years ago|reply
"Real-Time Health Monitoring The most significant innovation is the proprietary real-time hull health monitoring (RTM) system. Titan is the only manned submersible to employ an integrated real-time health monitoring system. Utilizing co-located acoustic sensors and strain gauges throughout the pressure boundary, the RTM system makes it possible to analyze the effects of changing pressure on the vessel as the submersible dives deeper, and accurately assess the integrity of the structure. This onboard health analysis monitoring system provides early warning detection for the pilot with enough time to arrest the descent and safely return to surface."
I am surprised that real time monitoring of the hull is even a consideration, I would have expected it to be designed an built with massive safety margins and then inspected very thoroughly after each trip. The above paragraph seems to indicate that they would monitor hull health during the trip and stop descent if it showed signs of stress. But I am skeptical that they would see signs of stress before it simply imploded at depth.
[+] [-] rodface|2 years ago|reply
https://www.whoi.edu/what-we-do/explore/underwater-vehicles/...
[+] [-] BXLE_1-1-BitIs1|2 years ago|reply
[+] [-] jugg1es|2 years ago|reply
[+] [-] WalterBright|2 years ago|reply
[+] [-] beowulfey|2 years ago|reply
[+] [-] iambateman|2 years ago|reply
But the company responsible is literally named OceanGate.
Some headlines write themselves.
[+] [-] saturn5k|2 years ago|reply
[+] [-] mongol|2 years ago|reply
[+] [-] shultays|2 years ago|reply
[+] [-] mikeyouse|2 years ago|reply
https://twitter.com/OceanGateExped
[+] [-] meghan_rain|2 years ago|reply
That being said,
> He added that because the passengers were sealed inside the vessel by bolts applied from the outside, "There's no way to escape, even if you rise to the surface by yourself. You cannot get out of the sub without a crew on the outside letting you out."
ouch
[+] [-] Mizoguchi|2 years ago|reply