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Comment by helios_invictus | Hacker News Reader

They do, but not the depths we're talking about (12,500 feet)

https://navalpost.com/how-deep-can-a-submarine-dive/ The depth limits of the most known nuclear powered submarines’ depth limits, as follows;

Typhoon-class: Test depth 900 m (3,000 ft) Astute-class: Over 300 m (984 ft 3 in) Akula-class: 480 m (1,570 ft) test depth for Akula I and Akula I Improved, 520 m (1,710 ft) for Akula II and III, 600 m (2,000 ft) maximum operating depth Ohio-class: Test depth >240 m (800+ ft) Virginia-class: Test depth >240 m (800+ ft) Borei-class: Test depth 950 m Rubis-class: Test depth 350 m Barracuda-class: Test depth >350 m

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> They do, but not the depths we're talking about

We really don’t know what depth the noise was comming from.

That being said it is vanishingly unlikely that an unrelated submarine trying to remain stealthy would be banging on their hull every half an hour.

Very true, it is a known factoid that submarines sometimes bump into each other because they can't tell that another sub is there. Doing so much noise as to be spotted from aircraft is crazy.

Strictly speaking I think it was buoys dropped from aircraft, it's not a listening device on the aircraft itself

Russia has a Losharik nuclear submarine that was tested up to 2500m (8200ft) if Wikipedia is to be believed. It got in the news when it had a fire that killed half a dozen decorated officers. USA probably has something similar.

No doubt, depth capability is one of the big features you go after when building a combat submarine. The deeper you go, the faster you can go while retaining stealth (cavitation is the limiting factor which decreases with the added hydrostatic pressure), and, if you can go significantly deeper than your adversaries, you're more or less invulnerable to attack because they can't shoot at you.

That's also why military specs on things like this are always lies, you don't want anyone knowing how deep you can actually go, which likely includes most of the crew.

Wouldn’t drag increase with the pressure?

I think I read in one of the earlier Titan threads this week that density increases pretty slowly with water depth. Water isn't very compressible, after all. So, to your question, I would guess "yes, but not by much".

It does, but, it's not terribly important given you're not limited by power output in a stealthy submarine.

Wow these numbers blow my mind. I imagined much deeper but some of these seem literally just below the surface.

'just below the surface' -> already at very impressive pressures and given the complex shape of their hulls absolute marvels of engineering. 240 meters below isn't 'just below the surface', that's pretty deep. That the ocean is much deeper is a simple fact but that should not diminish your appreciation for the differences between a 'regular' submarine and a deep sea vessel. Which is also why the latter tend to be extremely simple geometric shapes for the pressure vessel because of the stresses they are subjected to. Ball shape preferred, then cylinder. Something with angles in it would fail for sure.

Each ~30 feet or 10 meters adds an extra atmosphere of pressure. Recreation divers go to 120-130 feet (~4 extra atmospheres). Commercial divers go to ~1000 feet (~30 extra atmospheres). There are rumors that Navi divers can go to ~2000 feet (~60 extra atmospheres).

Not sure why somebody downvoted this. 'Just below the surface' is an odd phrasing, but I had the exact same sort of initial reaction as I think anybody would. The numbers are just so shocking here. The 'average' military sub isn't fit for travel much beyond 300 meters. The peak theoretic technology has subs that may be about to travel to around the 2000 meter mark.

The Titanic is at 3800 meters. That it's reachable, by private organizations no less, is just a marvel.

The Borei Class is not diving to 950 meters (unless its sinking) :)

Neither is the Typhoon.

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