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Yes but you also don’t want to operate so close to the safety margin. If you need to travel to 3800m, you design a sub to safely withstand 1.5x that. And then agreed that yes it should not implode right if it were to reach that depth. At least this is how I remember learning it, which I admit was a long time ago.

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> don’t want to operate so close to the safety margin.

How do you know they were operating close to their safety margin?

I think I’m misinterpreting what “rated for 4000m” means. My impression is this is the maximum safe depth the sub is capable of reaching without damage. And that they are bring it regularly to 95% of that depth.

My understanding of safety margins, as I was taught, is that one should design such that you have a safety margin of 1.5x the intended use case. In other words, for 3800m expected frequent usage, it should be able to reach a depth of 5700m.

Alvin, for example, can reach a depth of 6500m.

But you’re right, we don’t know what that 4000m means, really. I’m just assuming it means safe depth without damage.

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