I assume the metal and materials the boats are made of are strong but surely not to withstand the pressure of being 12,000 feet underwater? At the end of the day it’s not like the engineers had to consider holding up to that much pressure in their design right?
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Think about a soda can.
When it’s full, the inside is pressurized. That means there is MORE air pressure inside than outside. So when you try to squeeze it, that internal pressure pushes back against your hand. If you squeeze harder than that pressure, you’ll crush the can, but it’s really hard.
When it’s empty, that pressure is gone. The inside has the same pressure as the outside air. So when you push with your hand on the outside, there’s nothing inside pushing back that hard and the can is crushed easily.
The Titanic is open like the can. But the water pressure isn’t like your hand. The water on the “outside” of the Titanic has the same pressure as the water on the “inside” of the Titanic. So while water is pushing one way on the “outside”, there’s other water pushing the opposite way on the “inside”. If the Titanic were made out of a material that can compress like Styrofoam, it’d shrink due to all of this pressure. But it’s made out of metals that don’t really compress that way. They’re under a lot of stress, but they can take a lot of stress.
The submarine is a case where it’s more like we took some air out of the soda can and re-sealed it. Now the air on the outside is pushing HARDER on the can than the air inside. But the can’s metal still has some strength and can withstand some of that stress. If the outside air pushes harder than its ability to resist stress, the can will implode.
> At the end of the day it’s not like the engineers had to consider holding up to that much pressure in their design right?
Yes, they did. And one engineer had concerns. He was fired and is suing the company over it. [You can read a story here](https://newrepublic.com/post/173802/missing-titanic-sub-faced-lawsuit-depths-safely-travel-oceangate). I think this part of the story says a lot:
> Lochridge learned that the viewport manufacturer would only certify to a depth of 1,300 meters due to experimental design of the viewport supplied by OceanGate, which was out of the Pressure Vessels for Human Occupancy (“PVHO”) standards. OceanGate refused to pay for the manufacturer to build a viewport that would meet the required depth of 4,000 meters.
So the “viewport” of the sub was built to withstand water pressure at about 1,300 meters. The Titanic is in water at a depth of about 3,800 meters. That’s why the article mentions the required depth would be at least 4,000 meters. (I said “one engineer”, but that was just this article’s focus. If you really look in to this company, there have been many concerns from many people for a long time.)
This engineer saw, and reported, and knew everyone knew that the sub had materials not designed to handle the depths. The company responded to this by firing him. This is why it’s not good to trust eccentric billionaires who insist what they’re doing is safe and “sacrifices must be made”. They’re right an awful lot and when they are they advance science. But when they’re wrong, they’re catastrophically wrong. The problem is they tend to be right for a long time before the disaster happens, and they use that string of successes like a weapon to beat down people who raise concerns.
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