> [carbon fiber] solves some ballast issues (because a similar part out of steel or titanium would be far heavier and you can't discard the hull for obvious rea

> [carbon fiber] solves some ballast issues (because a similar part out of steel or titanium would be far heavier and you can't discard the hull for obvious reasons if you want to ascend). Incidentally there is another way they could have solved this problem; aluminum. With aluminum you can build a DSV that can dive deep enough to visit the Titanic, is light enough to not require additional buoyancy, and large enough to hold up to 7 people. This has been done: https://en.wikipedia.org/wiki/Aluminaut https://en.wikipedia.org/wiki/Aluminaut I think they probably had a fatigue life issue with an aluminum hull (it was only in service for six years..) since aluminum infamously has no fatigue limit. But it should be easier to characterize, so you can retire the hull before it fails.