Carbon fiber is a lot easier to work with than metal in this case because welding metal creates failure points. I don't think they could afford building a titanium pressure vessel. Weight is a factor too, carbon fiber is lighter so you can make the pressure vessel thicker and still have enough buoyancy to reach the surface(probably a good thing).

From their perspective it kinda made sense even though its not safe at all.

> I don't think they could afford building a titanium pressure vessel

If they could they probably still wouldn't have done so. The founder who was onboard the Titan was known for calling safety regulations unnecessary and a barrier to "innovation", like a window only rated for a depth of 1300m used at 4000m.

Obviously there seem to be some compelling reasons why the choice of a carbon hull was a faulty idea to begin with. The CEO would have been familiar with those critiques and proceeded anyway, presumably because of counter arguments he put more confidence in. Anyone out there familiar with what some of those counter points may have been?

“It was cheaper. Also I refused to hire subject matter experts because they were a bunch of 50 year old white men.”

Their website extensively mentions the acoustic monitoring system, with the thinking that any stress fractures would be detected prior to failure.

It probably did, but unfortunately, I think the window of time was not enough the return to the surface (perhaps milliseconds, but who knows)

No, it’s not easier to work with, unless you consider your work done completely once it’s manufactured without a thought to the ongoing testing and inspection regime required. And even then, laying CF is more niche than welding metal.

Carbon fibre is a ply. Plies are much harder to nondestructively inspect for flaws. That is an immediate, obvious risk in a use case involving cyclic pressure of hundreds of atmospheres. It is also brittle, so strain deformation does not occur nearly as much before fracture.

Welds are a vastly more well-understood feature that is possible to easily design around and - more critically - inspect afterwards. Metals also stretch before snapping, which is why you can go and measure the spacing of links on your bike chain and know when it’s time to replace it. All of this makes through-life maintenance and inspection much easier.

Carbon fibre was an incredibly poor design choice, selected to prioritise cost over safe operation.

Plain old steel seems to work and I'd imagine would be better given most subs are made of it. The Deepsea Challenger was made with 2.5 inch thick walls and went to 3x the depth. https://en.wikipedia.org/wiki/Deepsea_Challenger

I don't know and I'm not an SME, but it would seem weight always matter? For carrying, for bubbling up, etc.?

The main problem with steel is that it can only withstand such pressures if it's of spherical shape (i.e. a bathysphere). This usually only leaves enough room for two to three people (e.g. https://en.wikipedia.org/wiki/DSV_Alvin).

So it seems it's more a matter of cost and passenger space than just weight alone.