[aaronscott]

> Another simple risk mitigation step we take, that we believe to be unique to OceanGate is that we draw a small vacuum on the inside of the sub at the start of each dive. This step verifies the integrity of the low-pressure O-ring seal and eliminates the risk of leaks

I wonder what that low-pressure o-ring is sealing. I assume the vacuum would only simulate a one atmosphere differential, so that o-ring must not be sealing something exposed to the external pressures at the depths they go down to.

[noduerme]

One thing I'm curious about, as someone who knows nothing about the engineering of these things... why wouldn't anyone building something like this choose to over-pressure the sub once people were inside it and it began descending? Wouldn't 2 atmospheres inside represent a 50% reduction in the pressure differential on the hull at depth?

[icegreentea2]

Separate from the comments about pressure differential - even 2 atmospheres is probably enough to risk decompression sickness if they just popped the hatch at the end of the dive. So you'd need some way to reduce the pressure gradually. That either needs a way to vent gas out (which means adding a hole in the hull, which you'd really rather avoid having to deal with), or having a compressor inside the hull, or do the entire hatch popping in another pressure vessel. All of those options seem to odds with the 'go cheap and fast' approach.

[noduerme]

I'm not sure why it seems intuitive to me that the external to internal pressure ratio would be the measure of force exerted... i.e. that 2psi vs 1 would have the same net force as 100 vs. 50. I guess it's wrong, hence the responses, but it's still bothering me. Like, it seems intuitive that twice the mass in the same volume should exert twice the force on the inside of the container. I don't completely understand my error. Yes there's still 299 more atmospheres outside, but it's only 150x the inner pressure.

I'm not willing to concede this yet, I'll need to watch some youtube demos of why I'm a dumbass. hah.

As far as decompressing the hull on ascent, I was imagining that if they were testing it by pulling vacuum in it (as mentioned above) there must be some kind of auxiliary air release port...?

[BlueTemplar]

Pressure is Force / Area.

The materials must resist the net pressure, which is a vector addition, not division of vector's magnitudes one by another.

[zippothrowaway]

Outside pressure is 300 x atmosphere so a difference of 299 atmospheres. Increasing to 2 internally makes a difference of...298 atmospheres.

[robjan]

The internal pressure would have to be hundreds on atmospheres to offset the pressure outside. They would have to carry a lot more air at very high pressure on on the surface with more complicated and robust equipment to handle it. It would also make buoyancy management much harder. There's also the additional problem that there is a risk of gas narcosis above 3 atmospheres of pressure.

[noduerme]

So remember "The Abyss"? (James Cameron)... the aquanauts were living in a habitat that was pressurized at the bottom of the Mariana Trench or something. Was that just done before he realized it was physically impossible for humans to live in that kind of hyperbaric situation...? Or is it possible at any pressure with the right gas mixture?

[quickthrower2]

Not an expert so guessing but that would give you 299 atmospheres differential instead of 300. Also might be uncomfortable for the passengers?