3 ms·

There are non-trivial differences in designing vessels loaded with compression vs. tension, and the most experience we have is with internal pressure (e.g. tens

There are non-trivial differences in designing vessels loaded with compression vs. tension, and the most experience we have is with internal pressure (e.g. tension). The analysis is very nonlinear and unfortunately not as widely understood as internally pressurized vessels. It requires a lot more analysis, troubleshooting, and expertise that is short in supply. Add the additional catastrophic failure modes for composites and there's a reason that industry experts warned against this.

ajross 3y ago
With respect: that's exactly the kind of glib, drive-by analysis I'm talking about. What you're saying simply isn't true. People have been testing composites in pressure chambers and every load imaginable for decades. Yes, clearly they don't act like steel. But saying that it's impossible is just too easy. Just watch. It's going to be a routine design flaw, like they added a joint or a wiring hole in a bad place and didn't re-run the model. (Edit because this was misunderstood: I'm not saying what the failure is. I'm saying that we DON'T KNOW what the failure is, and that given the choice between makes-me-feel-smart pontification about materials and a routine design flaw in a prototype device, I'm going to bet on the routine failure every single time.)
- Johnny555 3y ago
  Just watch. It's going to be a routine design flaw, like they added a joint or a wiring hole in a bad place and didn't re-run the model. I like how you complain about people making glib drive-by analyses (that are at least based on actual submersible experts saying they shouldn't have used carbon fiber) by making a glib drive-by analysis that's based on pure conjecture.
  - ajross 3y ago
    It was a turn of phrase. I made the same point in a neutral, non-prescriptive manner (c.f "My gut says") upthread. Taking that sentence out of context is pretty poor form, whether you agree with me or not.
- causality0 3y ago
  I'm going to put my trust in the engineer who was overridden and fired for calling the thing a death trap before it killed five people. The thing was down-rated to 3000m and then it was used at 4000m therefore it imploded. I'd call that a management flaw more than an engineering flaw.
  - ajross 3y ago
    You're mixing things up. The hull that was downrated after inspection was a different submarine. The guy who was fired was an executive, not an engineer on the project (no idea about his background), and while he expressed concerns over safety he did not cite the use of carbon fiber as a problem (or at least it hasn't been reported that he did). Which is all to say: basing your opinions on this stuff on easily-consumed, tempting pseudoanalysis clickbait is a terrible way to figure out what went wrong. And in particular putting your ducks in this carbon fiber nonsense instead of "they probably just put a hole in the wrong place" seems poorly grounded to me.
    - fsckboy 3y ago
      Just want to say, I appreciate your contributions here, from one grizzled engineer to ... well, I don't know if you're grizzled, but I can tell you're a good engineer. Good engineering isn't a popularity contest, it's a thoroughness contest.
    - mustacheemperor 3y ago
      >while he expressed concerns over safety he did not cite the use of carbon fiber as a problem (or at least it hasn't been reported that he did). That’s exactly what I have seen reported. >But Lochridge, according to the suit, raised concerns about the design of the submersible's hull, particularly that it was made of carbon fiber instead of a metallic composition. https://abcnews.go.com/US/lawsuit-alleged-flaws-titanic-submersible-now-missing/story?id=100251012 https://abcnews.go.com/US/lawsuit-alleged-flaws-titanic-subm...

ajross 3y ago

With respect: that's exactly the kind of glib, drive-by analysis I'm talking about. What you're saying simply isn't true. People have been testing composites in pressure chambers and every load imaginable for decades. Yes, clearly they don't act like steel. But saying that it's impossible is just too easy. Just watch. It's going to be a routine design flaw, like they added a joint or a wiring hole in a bad place and didn't re-run the model. (Edit because this was misunderstood: I'm not saying what the failure is. I'm saying that we DON'T KNOW what the failure is, and that given the choice between makes-me-feel-smart pontification about materials and a routine design flaw in a prototype device, I'm going to bet on the routine failure every single time.)

Johnny555 3y ago
Just watch. It's going to be a routine design flaw, like they added a joint or a wiring hole in a bad place and didn't re-run the model. I like how you complain about people making glib drive-by analyses (that are at least based on actual submersible experts saying they shouldn't have used carbon fiber) by making a glib drive-by analysis that's based on pure conjecture.
- ajross 3y ago
  It was a turn of phrase. I made the same point in a neutral, non-prescriptive manner (c.f "My gut says") upthread. Taking that sentence out of context is pretty poor form, whether you agree with me or not.
causality0 3y ago
I'm going to put my trust in the engineer who was overridden and fired for calling the thing a death trap before it killed five people. The thing was down-rated to 3000m and then it was used at 4000m therefore it imploded. I'd call that a management flaw more than an engineering flaw.
- ajross 3y ago
  You're mixing things up. The hull that was downrated after inspection was a different submarine. The guy who was fired was an executive, not an engineer on the project (no idea about his background), and while he expressed concerns over safety he did not cite the use of carbon fiber as a problem (or at least it hasn't been reported that he did). Which is all to say: basing your opinions on this stuff on easily-consumed, tempting pseudoanalysis clickbait is a terrible way to figure out what went wrong. And in particular putting your ducks in this carbon fiber nonsense instead of "they probably just put a hole in the wrong place" seems poorly grounded to me.
  - fsckboy 3y ago
    Just want to say, I appreciate your contributions here, from one grizzled engineer to ... well, I don't know if you're grizzled, but I can tell you're a good engineer. Good engineering isn't a popularity contest, it's a thoroughness contest.
  - mustacheemperor 3y ago
    >while he expressed concerns over safety he did not cite the use of carbon fiber as a problem (or at least it hasn't been reported that he did). That’s exactly what I have seen reported. >But Lochridge, according to the suit, raised concerns about the design of the submersible's hull, particularly that it was made of carbon fiber instead of a metallic composition. https://abcnews.go.com/US/lawsuit-alleged-flaws-titanic-submersible-now-missing/story?id=100251012 https://abcnews.go.com/US/lawsuit-alleged-flaws-titanic-subm...