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Comment by sho_hn | Hacker News Reader

I was also curious about the timeline of this. I'm waiting for that one geeky blog post that integrates all the facts.

I'm particularly interested in an educated perspective on their choice in materials. I'm familiar with carbon fibre from bike frame building, and the common tricks/practices to try and look for fissures, find voids/delaminations, etc. after a crash, and it's such a complex subject and material. I wonder who manufactured this vessel and what the quality of their facilities, tools, processes was.

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My educated (a little bit of engineering at uni) perspective is: Completely idiotic to build a submarine out of carbon and not have the means for a complete inspection for manufacturing defects as the original article suggests.

Carbon, as you correctly note, needs to be very homogeneous. Bubbles, lamination defects or -god beware- fissures lead to failure, of the sudden, unannounced and total kind. And not only is it necessary to check after production, but also after regular short intervals of use, because a mere scratch in the carbon can be fatal.

It seems utterly bizarre to make a sub out of carbon fiber.

The advantage of CF is low weight. But who cares what a submarine weighs?

Some of the articles about it's construction indicate that many of the engineers were aerospace engineers.

I wouldn't want a submarine engineer designing a plane, and vice versa.

I was thinking about that but a steel sub can only really weigh as much as the same volume of water which probably limits things if you are going to 4000m. Too much weight and it'd sink like a stone.

> The advantage of CF is low weight. But who cares what a submarine weighs?

The heavier a sub is the bigger the ballast tanks have to be to compensate and the more energy is wasted on moving it, just like any other powered vehicle.

Do they even have ballast tanks? I saw mention of steel ballast they drop at the bottom.

The biggest benefit of reduced weight on this thing would be minimizing the size of the crane and surface vessel needed to deploy and recover it.

It's very bizarre. It's the first thing you learn about in materials engineering, in any mechanical/aeronautical engineering degree. We even made our own carbon fibre models (some with intentional defects) and tested failing them at my Uni.

I even get worried about cracks in my road bike. These guys are going 3km+ under water... It's insane.

It's also the only planned trip for the company this year due to weather. So the sub has sat for a period of time before being put in use.

Do you think they do extensive trial runs first at the beginning of each season? Like send it to the bottom un-manned just to double check?

As my former boss liked to say "Things that aren't tested don't work."

I think they can't even send it un-manned because it is not externally controllable. From what I understood in footage of a previous "mission", all is operated on board and there is nothing the ship crew can do appart from communicating (when it still works).

...well... Then clearly they should have put more time into the control system to allow for remote control from a submerged audio relay?

We've got more than enough ways to rig up signalling networks that there is zero reason for any submersible to not be remotely tested to crush depth.

I expect there will be a lot of books documenting every angle of this incident, if for no other reason than because of the Titanic connection. I'm looking forward to reading the whole story on how this incident happened.

https://www.youtube.com/watch?v=4dka29FSZac

Here is a quick and dirty analysis from a US Submariner of 20 years.

It is supposedly, incredibly hard to find defects or damage on carbon fiber. SpaceX did cite this as a reason for using stainless steel. His belief is that there was a hull failure somewhere on the carbon fiber hull; a failure point that simply wasn't found before this dive.

It depends on the material system they used. It is possible to scan for defects just need expensive equipment. Loading and unloading a sub like this could easily result in damages that aren’t detected though

I wonder if the NTSB will do a report on this.

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