OceanGate why would they make a 5600psi pressure hull of carbon fiber?

I don't know about OceanGate but carbon fiber is often used to save weight and still keep the same strength requirements. I wouldn't doubt that's why they did it. You can go bigger and still keep within the weight requirements. Carbon fiber is expensive relative to steel but in this case since they were looking to make it a tourist attraction then, I bet, it was economically advantageous. And in theory it can withstand an equal amount of pressure.

The big disadvantage is that when it fails it's catastrophic. It just shatters. There's no warning. At least with steel it bends before it fails. That's not the case with carbon fiber.

I completely fail to see how carbon fiber could be used to build what is essentially a vacuum vessel with 16,000 psi compressing it. You're basically counting on the compressive strength of the matrix it's embedded in to resist the forces involved, the fiber can only help resist cracking a bit.

It's pushing on a string... to me, that's just nuts.

Someone has to have a good explanation on how I'm wrong. If not, that makes it even more tragic.