That guy was a backyard inventor and charlatan, like those 19th century backyard aircraft inventors. It's one thing to take yourself out of the gene pool through your own recklessness, it's another to take others with you.
Rush bypassed over a hundred years of engineering lessons learned the hard way with the rationale it stifles innovation. He even fired and sued one of his own employees for calling him out on it. The sub had zero certifications and then he lied to customers about it saying his designs were approved by NASA and Boeing who never even heard of the guy.
Aside from the lack of safety engineering and lack of proper fail-safes in his design, there's a reason engineers don't use carbon fiber composites in subs. They have a tendency to delaminate. When used in aircraft, composites have to be examined and certified at a regular service interval with special inspection equipment.
I think that sub was an accident waiting to happen from day one. The hull probably failed due to inspection negligence and a failure to detect delamination. That's even if the hull could have been rated properly for 4km. If it wasn't the hull, it would been one of the other jury-rigged systems.
I can't believe people smart enough to acquire the wealth for that excursion weren't smart enough to check out the qualifications of the company hosting it. I think it was plainly obvious just looking at the sub yourself. A navigation system that consists of a consumer laptop PC and Logitech gaming controller should have been a dead giveaway.
