Its not the pressure, but the fact water blocks radio waves. Submarines can’t get GPS signals or transmit their location. Submarines have to rely on other means such as IMUs to track their own location.

What about a signal flare that floats to the surface?

I believe at a certain depth some things compress, density increases, buoyancy becomes negative - and they sink.

They have locator beacons size of a thermos (that ping powerfully using particular frequencies) which they fit on flights etc... i believe some can be received a couple miles+ down in good conditions like are seeing now.

But clearly not everything sinks, or the sub would never be able to surface. If it's just a matter of engineering work, that's kind of literally their job.

How would you track your location underwater? What's your reference?

They don't have any GPS signal down there...

With sonar. The submarine doesn't have to locate itself, it just needs to be active pinging and it can be triangulated.

Radio doesn't work underwater, but sound actually travels incredibly far (hence why military subs go all out with noise reductions).

Edit: I mean the real question is why the hell does this thing not have some type of system like this already? You know the upfront expected dive time, so set a couple of noisemakers on the exterior hull to go off after you exceed it.

I am not a marine noise expert, but it’s my understanding that noise transmits horizontally underwater way better than vertically. Since this sub is going really deep, getting the pings to go ‘up’ to a meaningful degree is going to be difficult.

This is correct, the different temperatured layers of water typically develope quite well defined borders, these border regions act like any border between mediums with differing densities: they refract and reflect waves passing through them.

Right: but even in then, you'd still be able to drop a microphone down through the layers and rapidly survey the whole thing at once. Much easier if the target is making a racket.

Good point, that could be used to the searchers advantage.

Just add a line. It's only 2 miles.

Apparently having a tether is not a bad option. So what’s the reason they didn’t go for it?

* * *

Possibly because they were closing in a wreck and a tether can get snagged

And I guess they were doing very close flyby, visibility down there is real bad.

yep, they have to get pretty close to see much. https://www.youtube.com/watch?v=UCwg2h7i4Ac

I’ve been wondering this too, and surprised that none of the news reports have addressed it. Would love to hear from someone knowledgeable on whether it’s feasible and what the limitations and trade-offs are (eg, unreasonably high risk of entanglement).

The most frustrating is reading somewhere, I can't remember, that there was some discussion about beacons after having lost comms during an excursion in the past. The conversation apparently didn't get there.

My first proper job in my career was IT for a maritime navigation company. This must have been around 2000, and we were selling these to normal people that have boats. I can't believe they did not integrate EPIRB into something like this triggered by an emergency trigger within the vehicle: https://en.wikipedia.org/wiki/Emergency_position-indicating_...

The facts that even if the unclear "7 ways" to surface in case of emergency, that a) the ship doesn't know where the submersible is located, which GPS would easily solve for and b) if it does manage to use one of these seven ways there's no way to exit the vehicle is absolutely criminal.