[bambax]

Yes, using carbon fiber was also a very bad decision; it was known for a very long time that it was only good for single-use sub, because after the first dive it was too damaged to continue. In 2014, Virgin Oceanic, which had similar plans with similar technology, closed shop because it didn't make economic sense to build a new sub for each dive.

But weight is absolutely an issue; the basic and tried-and-true metal sphere design allows for only three people. Since size and thickness grow exponentially, making a sphere for more than three people becomes more and more difficult. And it should also be possible to lift the vehicle with a crane.

But if you want to carry paying passengers (like Oceangate did), having only two per dive is very limiting. That's why they went with a tube design, and carbon fiber to limit weight. But it couldn't work, and it didn't.

[schiffern]

  >size and thickness grow exponentially

It's a [reverse] pressure vessel, so it follows pressure vessel scaling. Mass scaling is linear with internal volume.

[FabHK]

It’s funny how “literally” often means “figuratively” now, and “exponentially” means “polynomially”.

[bambax]

Yep.

https://books.google.com/ngrams/graph?content=exponentially%...

[bambax]

Ok yes "exponentially" was hyperbolic. Mass scales linearly with volume, but volume is proportional to the cube of the radius (not linear).

Also, in practice, small imperfections can have a disproportionate impact on the resistance of the sphere so design codes typically apply conservative reductions that can have a big impact on actual thickness requirements.

[wkat4242]

Did this thing meet any design codes though? I doubt it.

[donavanm]

I read the report when it come out. From memory, no. It never had any components or certification for human pressure vessels. IIRC theres no existing regs for carbon fiber and it would have cost like $50M to do the design and test work. They did buy some things, like the viewport, from companies who do certified parts, but instead opted for the same design minus any test certs to save money. The craft was never certified or inspected by the uscg. It did have a registration for a while, but they had to play find-a-new-district-sign-off shell games for a while, then… just stopped bothering.

[wkat4242]

Thanks for the detailed answer! It doesn't suprise me at all.