4 ms·

That's exactly it. If OceanGate had build and dropped a few dozen of these hulls empty, as many times as needed to reach failure, whatever design flaw caused t

by ajross 3y ago

That's exactly it. If OceanGate had build and dropped a few dozen of these hulls empty, as many times as needed to reach failure, whatever design flaw caused the implosion almost certainly would have been noticed. It's the hubris of diving in what amounts to a prototype that's at issue here, not any fundamental technical mistake.

throwanem 3y ago
Not even a prototype! More like a structural test article.
cactusplant7374 3y ago
It had already been down quite a few times. Do you mean 100's of drops? Although, couldn't they just leave it at the bottom for a month and see if it implodes?
- deleted 3y ago
  [deleted]
- deelowe 3y ago
  I thought the deepest it had gone was 3000 meters and there's no evidence of it even having been tested to 4k.
  - erik_seaberg 3y ago
    They had two successful trips to Titanic, and other tests in the Bahamas.
    - jonathankoren 3y ago
      So just enough times to weaken the hull through stress fractures. It wasn't rated for the depth. In fact, I think it was rated for 1000 meters less than the target depth.
    - deelowe 3y ago
      On the Titan? I thought this particular sub had never been down that far.
- foota 3y ago
  I believe the stresses of the hull going through changing pressures is relevant.
  - throw0101a 3y ago
    > I believe the stresses of the hull going through changing pressures is relevant. It certainly does for aircraft, and I doubt the material science would be much different for subs (with the added challenge(s) that (salt) water often brings): * https://www.smithsonianmag.com/air-space-magazine/what-determines-an-airplanes-lifespan-29533465/ https://www.smithsonianmag.com/air-space-magazine/what-deter... * https://simpleflying.com/pressurization-cycles-aircraft-lifespan/ https://simpleflying.com/pressurization-cycles-aircraft-life...
    - erik_seaberg 3y ago
      Worse, going from 1 atm down to 400 atm of pressure is a much larger difference than going up to 0.2 atm.
    - jsjohnst 3y ago
      Pressure at 330ft (aka 100m, way way shallower than Titanic depths) is 10 atmospheres higher than what it is at the surface. Even at 50k feet (higher than most planes operate) air pressure is still > 0.1 atmospheres. Titanic depths are around 380 atmospheres pressure. So equivalent to the difference of about 133,700 feet and sea level.
  - lamontcg 3y ago
    Definitely does for compressed gas cylinders.
- pengaru 3y ago
  > Although, couldn't they just leave it at the bottom for a month and see if it implodes? No, cyclic stresses are a different animal altogether. But considering it's just a matter of attaching ballast to sink it, dropping ballast to raise it, there's nothing preventing cyclic testing vs. static @ max depth over the same duration. It seems obvious to me that you'd want to burn through a few test hulls characterizing the fatigue limits and verifying they are at least consistent hull-to-hull with a deterministic failure point you can plan for retiring before approaching. You just need resources to burn on destroying enough hulls for the data. And there's a rub there; as you inform the process via destructive iteration, odds are you'll first find the manufacturing process isn't even controlled/consistent enough to make progress on answering the "so how many cycles before go boom boom?" question until you've gone through a good chunk of runway figuring out how to even make it properly multiple times.
  - _yb2s 3y ago
    This is a really good point... from what I've seen they estimated the strength with Finite Element Analysis in Solidworks, and went for a ~2x margin of safety. There seems to have been no attempt to experimentally determine the expected number of load cycles to failure, they only considered the theoretical case of a perfectly flawless composite with no wear and tear.
    - ShroudedNight 3y ago
      Is 2x abstractly reasonable in this context? My [probably flawed] understanding in contexts such as hoisting is that safety margins of 5x are considered a bare minimum. Even crappy "Don't use this to lift things" chain is sold with 3x margins.
      - _yb2s 3y ago
        Yes, I don't know what the norm is in submarines, but I don't really trust simple engineering models, and think at least 5x is what I'd want in almost any context. I did see that DeepFlight Challenger, Steve Fossett's unused/untested carbon fiber sub which used the same basic design as Titan, was only built to a 1.5x margin of safety. Experimental tests suggested it was only safe for a one time use, and shouldn't be used for multiple dives.
rossjudson 3y ago
I think a smaller N number of more dives would yield better results. Down, up, down up...repeat until failure. In parallel do it with another hull at the same time. Or maybe more than one. Compare. Testing to failure is a nice option because it finds certain types of unwelcome surprises. But it's not really complete, either -- there are probably a lot of ways that a submersible can be compromised, and there's no way to be sure what caused this particular failure.
- cbzoiav 3y ago
  The debris may yield significant clues. Those may then be able to be validated with independent testing rather than requiring a full vehicle.
hadlock 3y ago
The design flaw was that they used a construction material strong in tension, but weak in compression. For a task that is almost entirely compression. On a vehicle that has no need for weight savings. Also in a couple photos looks like they have drilled and screwed a monitor mount directly into the pressure vessel, creating future failure points, rather than gluing a piece of plywood to the hull and screwing into that, which is standard procedure.
- mustacheemperor 3y ago
  >On a vehicle that has no need for weight savings Most deep sea submersibles only seat a couple people, which wouldn't work for the 'titanic tourism carnival ride' business model. I would guess the weight savings were intended to enable a sub with more capacity that could still be winched on and off the support ship without more complex/expensive heavy lifting equipment.
  - wcfields 3y ago
    > the 'titanic tourism carnival ride' business model. That was more marketing; the main biz model was to create enough buzz with the oil/gas industry to get bootstrapped and produce a product fleet of cheap subs for independent contractors to use for oil rigs. https://www.fastcompany.com/40406673/the-man-who-wants-to-send-us-to-the-bottom-of-the-ocean https://www.fastcompany.com/40406673/the-man-who-wants-to-se... https://t.co/0ee7AImRRh https://t.co/0ee7AImRRh
    - nocoiner 3y ago
      I guess he didn’t know how safety conscious and risk averse the oil and gas industry actually is. You can be at a meeting in a conference room in downtown Houston, and they’ll start the meeting — like, every single one — with a safety minute and directions to the nearest stairwell. The operators with the kind of risk tolerance to support this kind of, uh, venture can’t afford to do deepwater exploration - that’s solely the domain of the industry mega-giants, which are the most safety conscious and risk averse of all. The odds of getting a contract with, say, Exxon for anything resembling that piece of shit submarine are just vanishingly small. I actually don’t think the accident makes that prospect any less likely - it was already about as close to 0 as you can get.

by ajross 3y ago

throwanem 3y ago

Not even a prototype! More like a structural test article.

cactusplant7374 3y ago

It had already been down quite a few times. Do you mean 100's of drops? Although, couldn't they just leave it at the bottom for a month and see if it implodes?

deleted 3y ago
[deleted]
deelowe 3y ago
I thought the deepest it had gone was 3000 meters and there's no evidence of it even having been tested to 4k.
- erik_seaberg 3y ago
  They had two successful trips to Titanic, and other tests in the Bahamas.
  - jonathankoren 3y ago
    So just enough times to weaken the hull through stress fractures. It wasn't rated for the depth. In fact, I think it was rated for 1000 meters less than the target depth.
  - deelowe 3y ago
    On the Titan? I thought this particular sub had never been down that far.
foota 3y ago
I believe the stresses of the hull going through changing pressures is relevant.
- throw0101a 3y ago
  > I believe the stresses of the hull going through changing pressures is relevant. It certainly does for aircraft, and I doubt the material science would be much different for subs (with the added challenge(s) that (salt) water often brings): * https://www.smithsonianmag.com/air-space-magazine/what-determines-an-airplanes-lifespan-29533465/ https://www.smithsonianmag.com/air-space-magazine/what-deter... * https://simpleflying.com/pressurization-cycles-aircraft-lifespan/ https://simpleflying.com/pressurization-cycles-aircraft-life...
  - erik_seaberg 3y ago
    Worse, going from 1 atm down to 400 atm of pressure is a much larger difference than going up to 0.2 atm.
  - jsjohnst 3y ago
    Pressure at 330ft (aka 100m, way way shallower than Titanic depths) is 10 atmospheres higher than what it is at the surface. Even at 50k feet (higher than most planes operate) air pressure is still > 0.1 atmospheres. Titanic depths are around 380 atmospheres pressure. So equivalent to the difference of about 133,700 feet and sea level.
- lamontcg 3y ago
  Definitely does for compressed gas cylinders.
pengaru 3y ago
> Although, couldn't they just leave it at the bottom for a month and see if it implodes? No, cyclic stresses are a different animal altogether. But considering it's just a matter of attaching ballast to sink it, dropping ballast to raise it, there's nothing preventing cyclic testing vs. static @ max depth over the same duration. It seems obvious to me that you'd want to burn through a few test hulls characterizing the fatigue limits and verifying they are at least consistent hull-to-hull with a deterministic failure point you can plan for retiring before approaching. You just need resources to burn on destroying enough hulls for the data. And there's a rub there; as you inform the process via destructive iteration, odds are you'll first find the manufacturing process isn't even controlled/consistent enough to make progress on answering the "so how many cycles before go boom boom?" question until you've gone through a good chunk of runway figuring out how to even make it properly multiple times.
- _yb2s 3y ago
  This is a really good point... from what I've seen they estimated the strength with Finite Element Analysis in Solidworks, and went for a ~2x margin of safety. There seems to have been no attempt to experimentally determine the expected number of load cycles to failure, they only considered the theoretical case of a perfectly flawless composite with no wear and tear.
  - ShroudedNight 3y ago
    Is 2x abstractly reasonable in this context? My [probably flawed] understanding in contexts such as hoisting is that safety margins of 5x are considered a bare minimum. Even crappy "Don't use this to lift things" chain is sold with 3x margins.
    - _yb2s 3y ago
      Yes, I don't know what the norm is in submarines, but I don't really trust simple engineering models, and think at least 5x is what I'd want in almost any context. I did see that DeepFlight Challenger, Steve Fossett's unused/untested carbon fiber sub which used the same basic design as Titan, was only built to a 1.5x margin of safety. Experimental tests suggested it was only safe for a one time use, and shouldn't be used for multiple dives.

rossjudson 3y ago

I think a smaller N number of more dives would yield better results. Down, up, down up...repeat until failure. In parallel do it with another hull at the same time. Or maybe more than one. Compare. Testing to failure is a nice option because it finds certain types of unwelcome surprises. But it's not really complete, either -- there are probably a lot of ways that a submersible can be compromised, and there's no way to be sure what caused this particular failure.

cbzoiav 3y ago
The debris may yield significant clues. Those may then be able to be validated with independent testing rather than requiring a full vehicle.

hadlock 3y ago

The design flaw was that they used a construction material strong in tension, but weak in compression. For a task that is almost entirely compression. On a vehicle that has no need for weight savings. Also in a couple photos looks like they have drilled and screwed a monitor mount directly into the pressure vessel, creating future failure points, rather than gluing a piece of plywood to the hull and screwing into that, which is standard procedure.

mustacheemperor 3y ago
>On a vehicle that has no need for weight savings Most deep sea submersibles only seat a couple people, which wouldn't work for the 'titanic tourism carnival ride' business model. I would guess the weight savings were intended to enable a sub with more capacity that could still be winched on and off the support ship without more complex/expensive heavy lifting equipment.
- wcfields 3y ago
  > the 'titanic tourism carnival ride' business model. That was more marketing; the main biz model was to create enough buzz with the oil/gas industry to get bootstrapped and produce a product fleet of cheap subs for independent contractors to use for oil rigs. https://www.fastcompany.com/40406673/the-man-who-wants-to-send-us-to-the-bottom-of-the-ocean https://www.fastcompany.com/40406673/the-man-who-wants-to-se... https://t.co/0ee7AImRRh https://t.co/0ee7AImRRh
  - nocoiner 3y ago
    I guess he didn’t know how safety conscious and risk averse the oil and gas industry actually is. You can be at a meeting in a conference room in downtown Houston, and they’ll start the meeting — like, every single one — with a safety minute and directions to the nearest stairwell. The operators with the kind of risk tolerance to support this kind of, uh, venture can’t afford to do deepwater exploration - that’s solely the domain of the industry mega-giants, which are the most safety conscious and risk averse of all. The odds of getting a contract with, say, Exxon for anything resembling that piece of shit submarine are just vanishingly small. I actually don’t think the accident makes that prospect any less likely - it was already about as close to 0 as you can get.