Comment by dwheeler | Hacker News Reader

Comment by dwheeler | Hacker News Reader

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> The thing that I find amazing about this sub, is that the final hull survived all those trips, and then before the final one let everyone know it was toast, and Stockton ignored it. He was careless with peoples lives, but his sub actually did what he set out to do, and if he listened to the instruments, he'd still be alive...

I disagree. In fact, I think that's quite unlikely.

First, unlike a metal hull, carbon fiber hulls accumulate subtle damage on compression that's hard to detect. Then, when they fail, they tend to fail catastrophically. So "this hull worked before" isn't evidence of success in this case, as it normally would be, it's evidence that you're getting closer & closer to the disaster.

Second, I think Stockton would have just kept diving, even if this event hadn't failed. He might have even gotten more reckless (though per the report he was already extremely reckless). If you keep playing Russian Roulette, and occasionally add another bullet, eventually the game will end. There is no evidence he was going to stop until he was killed by his own decisions.

None of this takes away the tragedy of it. It's sad, and will remain so.

> unlike a metal hull, carbon fiber hulls accumulate subtle damage on compression that's hard to detect

All metals suffer from that, too. It's called fatigue damage. It bedeviled the aviation industry for a long time because there was no reliable way to detect the fatigue damage.

Eventually, an ad hoc formula was developed to calculate the fatigue damage, and then replace parts that were getting close to the limits.

That's why airliners are scrapped after something like 62,000 flight cycles.

The standard testing for submarine involves 1000 cycles of going to full depth/pressure and up. And depth higher then the target depth.

Only after that you can use it for paying passangers. This submarine survived the depth around 23 times. (Most of the "trips" were 3m deep)

Aluminum is especially bad this way. And we make airplanes out of it.

And if you're USAF, you practically strip the aircraft to its frame every few years, inspect, repair, and reassemble it. The dangers are known and the process around it is there to deal with those dangers.

Most aircraft fleets operated by people who care will do something similar but perhaps not as extreme. In fairness to them they don't expect to fly the plane as long as USAF does (70+ years for the B-52, 50+ for many fighters).

These days it's carbon fiber.

Not all of them. The 787 yeah, but it seems the 747-8 is still somewhat metal.

I think you missed the thrust of OP. The submersible had instruments in it to report on the hull condition. They all were reporting it had previously experienced severe strain before the last dive, and they were designed as tripwires. If they tripped, the hull should have been considered unsafe and not used again. They were ignored.

It is a shock that they actually worked and reported the hull was unsafe before it failed. Given everything else, it's not a surprise in the slightest that they were ignored.

To be extra clear here:

They used an unproven custom-designed sensor + controller system to monitor the health of the hull.

The monitoring system detected the beginning of total hull failure in the exact way they intended. They then ignored that monitoring system because hull failure would have been inconvenient.

Really that's the whole story of Stockton here. Massively motivated reasoning. Anything inconvenient was written off as wrong. A lot of normalization of deviance too as some of the written-off concerns turned out to be wrong. But not all of them.

I recently got my PPL and that's a massive risk for pilots. You fly in weather you shouldn't and get away with it for a while. Then it becomes normal. You've "proven" you can handle it. Then a situation comes along that requires more margin than you have left and you die.

Exactly, the hull performed, then the instruments told them with a loud bang that it was toast.

Once again... The instruments reported the hull was no longer safe for use before the start of the last dive. That was well before the implosion. You keep ignoring this part to focus on how there was no engineering that would suggest that those instruments would actually give early warning. I'm halfway there with you. It is actually a surprise that they reported it was unsafe before the dive. But they did, and that makes the subsequent human failures even more egregious.

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