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Comment by TazeTSchnitzel | Hacker News Reader

The hull was made from 5-inch thick carbon fibre. Carbon fibre is very lightweight for such a strong material, which makes it attractive, but it has a few critical downsides:

• it tends to fail catastrophically, without warning, after repeated stress

• it's very difficult to predict how many stress cycles it can endure

• it's very difficult to detect stress cycle damage

Considering every dive and resurface is a huge stress cycle, and the fact OceanGate didn't seem to have any sort of independent certification of their submersible's endurance, this kind of hull implosion event seems inevitable. Their real-time hull monitoring system was a boondoggle, n

Edit: In another interview, Cameron elaborated on these exact concerns: https://www.youtube.com/watch?v=V-yu_wixdgE&t=1m20s

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An important note is that an employee was (allegedly) fired for making a point that the carbon fiber was two inches too thin.

They also apparently didn't even report it until 8 hours after noticing it didn't resurface once communications stopped.

If that's true, James Cameron's assessment rings true.

What's the benefit of carbon fiber's strength-to-weight ratio when making a submersible?

I guess you can have smaller motors to drive you around on the bottom, but the vast majority of the travel is controlled via ballast/buoyancy.

To me, planes and cars have much more obvious gains from lighter materials. Not so much for the sub.

The submersibles need to be less dense than water on average so they rise when you release ballast.

It's always a cost tradeoff - I think Challenger Deep (Cameron's former sub) was steel construction which required a large volume of syntactic foam that can resist high pressures to counteract the weight of the steel. That makes for a much larger vessel.

Titan's submersible for exploring the Mariana Trench I believe is largely titanium so much lighter than steel, but at a hugely increased cost.

I'm not sure why I highlighted that because indeed that wouldn't be useful, though as a proxy for density it is (apparently they picked it for its buoyancy).

> What's the benefit of carbon fiber's strength-to-weight ratio when making a submersible?

Not having to bond expensive foam to it to make it buoyant. I also think it may have something to do with the shape of the hull in this case, but I have not seen any commentary on that yet.

Right - the first thought which came to my mind - there was only one prototype sub, had it been tested for say a dozen trips? What happens? how much wear and tear, all that stuff you don't call out in the agreement to opt-in to death.

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