Submersible missing while visiting Titanic wreck

[hans]

Looking at the non-linearity increasing in every dive after 80 should have been a total red flag.

That's only apparent if you compare previous dives by overlaying the data as shown, and even then it's not that noticeable unless you're looking for something - anything - to explain a catastrophe. I bet they didn't compare, or if they did only superficially, and instead were looking for something much more obvious - a spike or dent, perhaps - and at depth rather than wallowing about in the wave field.

That it was happening at relatively shallow depths makes it look as if it needed some increasing pressure to force the (now partially unglued) 5 layers back together.

Again, obvious in hindsight. But that it was only at shallow depths perhaps mitigated. Where it really mattered, at proper depths, it looked normal.

They supposedly hired someone that would look at this data intensely after dive. They collected it after all, which they wouldn't do if they didn't care to use it.

It should be obvious because the uncompressed steady state had changed. If they took measurements in their garage, they should have seen quite dramatic different readings (+/-10% or greater) on a bunch of strain sensors. If they even had just pressure cycled the hull to some shallow depth, they could have compared depth-strain plots to draw the same conclusions

No the design wasn't good enough. The last video explains that the minimum safety margin to get any kind of certification would have been 1.25 and they didn't achieve that. They didn't have any certificate that allowed them to dive with humans inside.
Then there are the doubts about leaving the submersible in a parking lot exposed to winter weather for several months. Did they realize it was bad and were giving up? If they changed their minds later for some reason (probably money), then the whole story is already close to criminal intent.

Their negligence of a proper safety factor is IMO a good quantification of the whole approach to this sub. This sub lasted only a dozen or so dives at depth. Maybe they could have built a sub that would last hundreds of cycles if only had 0.5 - 1 inch of more CF? It would presumably have taken the peak strain/load of everything by a lot, although it still relies on proper manufacturing to hold everything in place (and perhaps proper tooling to fabricate/test).

It looks like they weren't completely crazy with this design. There was some measures in place to prevent premature failure. But some design decisions and the safety culture was very poor. And I think some of them came down to very poor judgements. E.g. their risk assessment sheet had tons of weird factors included. Apparently having media/celebrities on board was a greater risk than performing the first dive after a previous repair job (as that got zero points). These documents were described as safety theater, or alternatively, it was perhaps more of a commercial safety factor (failed dive=money lost) rather than operational.

Regarding safety factor an offtopic example: a friend of mine said a while back: "I drive through this highway onramp corner at 80km/h no problem" (recommended speed was 50). At which I replied: on a particularly "youthful" hot summer day I was driving 90km/h, got into a slide, which fortunately I was able to correct since otherwise I would have folded my car around a tree (which would have been fatal). So perhaps the "optimal speed" would have been 85km/h.
But in this case, why risk flying so close to the moon? How do you know how far 80km/h is under the physical capability of your car? And is that 10%, 25% or 50% off? And what figure do you pick? Sure its exciting to drive at <10% margin from time to time.. but it's all but safe. What if your tyres got a bit worse, the road is greasy, etc.? Judgements like these play with probability theory.

In this case they knew their sub had a safety factor of less then 1.1 IIRC, and they also know that cycling effects will degrade the strength over time. Operationally they failed to catch the fault, but the whole approach was shady.
Both were particularly ill judgements that look like they could have been prevented.

[tom66]

As I recall, one of the reasons for using CF was it made the sub less buoyant.  A full steel construction would have been too heavy to sink without ballast tanks, which would increase the size and cost of the sub.  It's possible that adding another layer of CF, along with increasing the rest of the sub's size (in particular those titanium rings and domes can't have been lightweight), would have substantially reduced buoyancy.  Rush was all about the CF hull, but perhaps it just wasn't possible to make one safe in this configuration, and his 'need' to see it happening blinded him to the obvious risks.