3 ms·

> Although, couldn't they just leave it at the bottom for a month and see if it implodes? No, cyclic stresses are a different animal altogether. But consideri

> Although, couldn't they just leave it at the bottom for a month and see if it implodes? No, cyclic stresses are a different animal altogether. But considering it's just a matter of attaching ballast to sink it, dropping ballast to raise it, there's nothing preventing cyclic testing vs. static @ max depth over the same duration. It seems obvious to me that you'd want to burn through a few test hulls characterizing the fatigue limits and verifying they are at least consistent hull-to-hull with a deterministic failure point you can plan for retiring before approaching. You just need resources to burn on destroying enough hulls for the data. And there's a rub there; as you inform the process via destructive iteration, odds are you'll first find the manufacturing process isn't even controlled/consistent enough to make progress on answering the "so how many cycles before go boom boom?" question until you've gone through a good chunk of runway figuring out how to even make it properly multiple times.

_yb2s 3y ago
This is a really good point... from what I've seen they estimated the strength with Finite Element Analysis in Solidworks, and went for a ~2x margin of safety. There seems to have been no attempt to experimentally determine the expected number of load cycles to failure, they only considered the theoretical case of a perfectly flawless composite with no wear and tear.
- ShroudedNight 3y ago
  Is 2x abstractly reasonable in this context? My [probably flawed] understanding in contexts such as hoisting is that safety margins of 5x are considered a bare minimum. Even crappy "Don't use this to lift things" chain is sold with 3x margins.
  - _yb2s 3y ago
    Yes, I don't know what the norm is in submarines, but I don't really trust simple engineering models, and think at least 5x is what I'd want in almost any context. I did see that DeepFlight Challenger, Steve Fossett's unused/untested carbon fiber sub which used the same basic design as Titan, was only built to a 1.5x margin of safety. Experimental tests suggested it was only safe for a one time use, and shouldn't be used for multiple dives.
  - flaminHotSpeedo 3y ago
    Depending on the context 2x is within the realm of reasonable for things like aircraft. But yeah for stuff like bridges you're probably looking at something closer to 20x
cbzoiav 3y ago
> You just need resources to burn on destroying enough hulls for the data. Unmanned submersibles have plenty of market value. You may still be losing money, but you can strap sensors and cameras to the thing / undercut on price for research missions and substantially reduce the cash burn while building investor confidence.
- cactusplant7374 3y ago
  So Stockton Rush had a lot of options to make money during extensive testing? He made it sound like the company would go under.
cactusplant7374 3y ago
Each time they go down they have to jettison some waste to return to the surface?
- pengaru 3y ago
  I'm no sub nerd but it seems obvious that unless you can otherwise alter your buoyancy somehow, your only option is to drop weights. I think submarines use ballast tanks they flood with sea water and empty with pumps to vary their buoyancy. Titan had none of that complexity AIUI, and multiple articles I read mentioned dropping "ascent weights".
  - Gwypaas 3y ago
    You can use compressed air. The COPV Spacex uses for tank pressurization are rated higher than the Titanic depth. And as depth increases the differential decreases. So you really only care about their structural integrity at the surface.
    - pengaru 3y ago
      Which would be an actual appropriate application for carbon composite...
  - dm319 3y ago
    Ballast tanks don't work at these depths because of the extreme pressure, which is why all these deep sea vehicles are submersibles rather than submarines. In fact I think if a submarine goes below a certain depth then it can't adjust its buoyancy to return to the surface again, but I am also not a sub nerd.
wcfields 3y ago
How could you figure it out if you’re using Boeing surplus carbon fiber that’s past its shelf life. [1] Your data will be all over the place from surplus to surplus sale. [1] https://www.insider.com/oceangate-ceo-said-titan-made-old-material-bought-boeing-report-2023-6 https://www.insider.com/oceangate-ceo-said-titan-made-old-ma...

_yb2s 3y ago

This is a really good point... from what I've seen they estimated the strength with Finite Element Analysis in Solidworks, and went for a ~2x margin of safety. There seems to have been no attempt to experimentally determine the expected number of load cycles to failure, they only considered the theoretical case of a perfectly flawless composite with no wear and tear.

ShroudedNight 3y ago
Is 2x abstractly reasonable in this context? My [probably flawed] understanding in contexts such as hoisting is that safety margins of 5x are considered a bare minimum. Even crappy "Don't use this to lift things" chain is sold with 3x margins.
- _yb2s 3y ago
  Yes, I don't know what the norm is in submarines, but I don't really trust simple engineering models, and think at least 5x is what I'd want in almost any context. I did see that DeepFlight Challenger, Steve Fossett's unused/untested carbon fiber sub which used the same basic design as Titan, was only built to a 1.5x margin of safety. Experimental tests suggested it was only safe for a one time use, and shouldn't be used for multiple dives.
- flaminHotSpeedo 3y ago
  Depending on the context 2x is within the realm of reasonable for things like aircraft. But yeah for stuff like bridges you're probably looking at something closer to 20x

cbzoiav 3y ago

> You just need resources to burn on destroying enough hulls for the data. Unmanned submersibles have plenty of market value. You may still be losing money, but you can strap sensors and cameras to the thing / undercut on price for research missions and substantially reduce the cash burn while building investor confidence.

cactusplant7374 3y ago
So Stockton Rush had a lot of options to make money during extensive testing? He made it sound like the company would go under.

cactusplant7374 3y ago

Each time they go down they have to jettison some waste to return to the surface?

pengaru 3y ago
I'm no sub nerd but it seems obvious that unless you can otherwise alter your buoyancy somehow, your only option is to drop weights. I think submarines use ballast tanks they flood with sea water and empty with pumps to vary their buoyancy. Titan had none of that complexity AIUI, and multiple articles I read mentioned dropping "ascent weights".
- Gwypaas 3y ago
  You can use compressed air. The COPV Spacex uses for tank pressurization are rated higher than the Titanic depth. And as depth increases the differential decreases. So you really only care about their structural integrity at the surface.
  - pengaru 3y ago
    Which would be an actual appropriate application for carbon composite...
- dm319 3y ago
  Ballast tanks don't work at these depths because of the extreme pressure, which is why all these deep sea vehicles are submersibles rather than submarines. In fact I think if a submarine goes below a certain depth then it can't adjust its buoyancy to return to the surface again, but I am also not a sub nerd.

wcfields 3y ago

How could you figure it out if you’re using Boeing surplus carbon fiber that’s past its shelf life. [1] Your data will be all over the place from surplus to surplus sale. [1] https://www.insider.com/oceangate-ceo-said-titan-made-old-material-bought-boeing-report-2023-6 https://www.insider.com/oceangate-ceo-said-titan-made-old-ma...