The thing that I find amazing about this sub, is that the final hull survived all those trips, and then before the final one let everyone know it was toast, and Stockton ignored it. He was careless with peoples lives, but his sub actually did what he set out to do, and if he listened to the instruments, he'd still be alive, he could have made another hull, and he could be taking more trips down there for better of for worse. The porthole design was poor, the carbon fiber had tons of defects, the controller, everything was cobbled together, yet it held up until it didn't.
It didn't implode on next dive, it was much worse.
On dive 80 during surfacing people heard a "loud bang" from the submersible (according to a witness it sounded like a gunfire).
They looked at their "RTMS" system and found recording of loud noise from the hull. But only three days later they did the dive 81 (with customers). After this dive their tension sensors shown that their carbon hull no longer compresses under pressure like it used to. They then made plan to inspect the hull after dive 83. But instead they left Titan winter on the parking lot in Saint Johns where it was not protected from any exposure because that was cheaper.
During summer they hauled it for a dive 88 (I don't know why they jumped from 81 to 88, prolly cancelled dives because of the weather?). During hauling it become loose and started knocking against the hauling platform (LARS) because of the waves. Day later they did a dive where it imploded.
On side note, they had no way to access and inspect the carbon hull without having to completely dissemble vehicle, and that too was considered too pricy to do.
This was a disaster of organization with messianic CEO dismissing all concerns with bravado and legal treats that got what was coming to them. If you want to, here's transcript of him scolding and then laying out one of engineers because they took safety concerns outside of the company:
"Not at all, because carbon fiber is better compression then tension. And that's what nobody understands. It's completely opposite of what everyone else says. Everyone's, oh, carbon fiber can't handle compression. They're full of shit, and I've proven they're full of shit."
"Now, if it fails, then you have to stop, and it's -- again, this is not something that just happens all of a sudden. It doesn't just implode. It screams like a mother before it implodes."
- Man crushed by an instantly imploding submersible
Right next to the O-rings will survive in temperatures colder than they were designed. At least Rush's backside cashed the check his mouth wrote where as the NASA engineers were still around after their decision. Does that make one better/worse than the other? Rush took other people with him though when he cashed that check.
Why? There’s already a plentiful list of disastrously wrong arrogant cocksure assholes. Still doesn’t stop people from thinking they’re the Steve Jobs flavor of arrogant cocksure asshole.
Being weaker in compression than in tension is not the same as being unable to handle compression. 40% of carbon fiber's tensile strength is still comparable to the compressive strength of high strength steel.
As 95% of the carbon fiber market is T300, and as T300 hasn't changed in the years since, I think it holds up.
Long story short, raw carbon fiber has a high compressive strength, but it's still just ~40% of its tensile strength. Carbon fiber composite single-plies or tapes have a reduced, but still reasonably high, compressive strength. When you get to multi-ply 0/90° or 0/45/90° composite laminates, "allowable" A-Basis (<1% likelihood of failure) compressive strength is very low -- around 400MPa -- well under the compressive strength of good steel.
And that's under ideal conditions. You've got to apply knock-downs for ply angle, moisture, through-thickness shear, impact damage, and manufacturing defects.
...Hence the Titan sub failed at a compressive load of something like 200MPa.
I'm not accusing you of this, but one of the issues with carbon fiber is that people see on a specsheet that it has, e.g., a "tensile strength = 4000MPa" and they assume that composite parts will exhibit a practical tensile strength of 4000MPa. The properties of CFRP -- CF composites with epoxy or PEEK or whatever -- are always way reduced, and sometimes quite difficult to pin down.
That said, the tensile strength of CF is always high, as a rule of thumb. Its compressive strength really isn't.
I would not call 400 MPa "very low" that's better than the best structural steel. Further, the important thing is the specific strength. CFRP has a density 5 times lower than steel, meaning you can use 5 times as much for the same weight, bearing 5 times the load. A good steel has a compressive strength around 1000 MPa, the best superalloys have compressive strength around 1500 MPa, the same weight of CFRP can withstand the equivalent of around 2000 MPa.
Sure this is idealized, but so is the strength of steel.
The concern with carbon fiber is its potential for delamination, not its compressive strength. Titan's failure was after delamination.
400 MPa is not better than the best structural steel. And 1000 MPa is way higher than the best structural steel (compressive strength and tensile strength are essentially equal for steel). Most structural steel has an ultimate tensile strength of around 500 MPa. Ultimate tensile strength is the comparable strength parameter when discussing rupture/fracture.
400 MPa is better than the best structural steel. 1000 MPa is not for structural steel, it is for high grade steel, the sort you make submarines out of. Why would I list 400 and 1000 for the same value?
Steel is weaker in compression than tension. It's more isotropic than say concrete, but the difference is meaningful in practice.
We're not discussing rupture here. That's for when the pressure is higher internally than externally. We are discussing a submarine, which is a pressure vessel under compression which must also remain buoyant. The specific yield compressive strength is the value which matters.
When someone says "structural steel" they are normally talking about something similar to A572. A572 comes in multiple grades, with grade 42 being the lowest. Grade 42 has a yield strength of 42 ksi (hence grade 42) and a rupture strength of 60 ksi by spec. 60 ksi is 414 MPa. Even A36 (which is basically the weakest structural steel commercially available nowadays) has a rupture strength of around 60 ksi and a yield strength of 36 ksi. Hence, even the weakest "structural steels" have a rupture strength of around 400 MPa.
When I use the word "rupture" I am talking about the material property, not the specific submarine loading condition at play. When comparing steel, which is a ductile material, to carbon fiber, which is a brittle material, you should use the steel's rupture strength instead of yield strength. Steel is for all intents and purposes an isotropic material, and the difference between tensile strength and compressive strength is not material in practice (because steel in compression is nearly always governed by macro-scale geometric issues leading to buckling rather than the material strength in compression being exceeded).
The '~' is important: composites are in general very difficult to predict, and under compression even more so.
(To build some intuition: carbon fibre, is just that, i.e. a fabric. No-one expects to be able to push on the edges of a sheet of fabric get any real resistance at all. If you then embed that it a plastic, i.e. make a composite, the plastic is mainly what makes it hold its shape. It's only really made stronger in tension by the fibers in it, why would you expect the compression to be better?)
> But instead they left Titan winter on the parking lot in Saint Johns where it was not protected from any exposure because that was cheaper.
This came up in the hearings. It's standard practice to do this but it's probably different leaving say the metallic Antipodes [1] outside than carbon fiber.
The report here more or less outright says that leaving it outside was a major factor in the incident. The incident on dive 80 was adjudged to be partial delamination of the carbon fiber layers, and leaving it outside subjected it to freeze-thaw cycles that propagated the delamination into near-total delamination, which promptly failed the next time the hull was pressurized. Although there is also the aborted dive 87, which subjected to the submersible to a lot of percussive damage via wave action.
One wonders if any of these people have ever heard the term, "Don't poke the bear."
Reading this is like watching someone gamble their life savings away because they know the next round/hand is gonna be the one where they win it all back.
Some real gems here and learned some things I wasn't aware of.
> "Now, if it fails, then you have to stop, and it's -- again, this is not something that just happens all of a sudden. It doesn't just implode. It screams like a mother before it implodes."
> On dive 80 during surfacing people heard a "loud bang" from the submersible (according to a witness it sounded like a gunfire)
Well, there you go.
> But instead they left Titan <during the> winter on the parking lot in Saint Johns where it was not protected from any exposure because that was cheaper.
> During hauling it become loose and started knocking against the hauling platform (LARS) because of the waves. Day later they did a dive where it imploded.
Early on, it was made clear that carbon fiber hulls could not easily be inspected for integrity issues like metal hulls can be. I'm not an expert, but I'm guessing sensitive instruments have been around for a while for the purpose of inspection. Having a hull you cannot easily inspect would/should make most people/companies nervous.
This transcript is of CEO Stockton Rush interviewing redacted "Director of Marine Operations"? Do I have that right?
Why is there a transcript of the CEO interviewing one of his own employees, apparently in front of the NTSB, from 2018?
Edit: the transcript is between Stockton Rush and his former director of marine operations, David Lochridge, plus three other staff. [...] Lochridge: "That meeting turned out to be a two-hour, 10-minute discussion… on my termination and how my disagreements with the organisation, with regards to safety, didn't matter." [...] The 2018 meeting was recorded.
> They then made plan to inspect the hull after dive 83. But instead they left Titan winter on the parking lot in Saint Johns where it was not protected from any exposure because that was cheaper.
The things I'm working on have a much lower (zero?) chance of death but this is a tale as old as time. _Looks longingly into the backlog..._
> This was a disaster of organization with messianic CEO dismissing all concerns with bravado
While I love this list, I do not like that you are blaming everything on CEO.
This company followed current ethical policies, and used them to exclude actual experts and skilled people. CEO operated in environment that supports this behaviour, and only cares about irelevant metrics!
Its fair to blame Stockthon because he fired or treated to sue everyone who didn’t buy into his spiel about this being revolutionary disruption of private submarines. Leves of staff rotation were insane in this company, their lead eng. at the time of implosion was a software dev because everybody else left or was laid off.
High staff rotation is typical for such companies. Qualified person with other options, will not work in such toxic company, after CEO had racist and ageist rant!
My point is where such companies get funding?! They produce garbage and should go bankrupt pretty fast! But somehow "investors" kept feeding them money, because they are super "ethical"!
his critics were silenced? bro they were loud as hell and consistently so.
the dude did everything he could to fly under the radar, but only just enough. it is why the report is so damning -- much of what he did was just blatantly, balls-out bad, and all of the signs were there consistently.
But that person is right. Co owners, board and even layer that knowingly helped to relatiate against whistle blower with fake accusations are all guilty too. At least in the ethical sense.
Rush is dead, so it is comfortable for the above to blame only him.
The board knew about the issues. The layer knew the accusation is fake and designed to shut up the whistleblower.
> The thing that I find amazing about this sub, is that the final hull survived all those trips, and then before the final one let everyone know it was toast, and Stockton ignored it. He was careless with peoples lives, but his sub actually did what he set out to do, and if he listened to the instruments, he'd still be alive...
I disagree. In fact, I think that's quite unlikely.
First, unlike a metal hull, carbon fiber hulls accumulate subtle damage on compression that's hard to detect. Then, when they fail, they tend to fail catastrophically. So "this hull worked before" isn't evidence of success in this case, as it normally would be, it's evidence that you're getting closer & closer to the disaster.
Second, I think Stockton would have just kept diving, even if this event hadn't failed. He might have even gotten more reckless (though per the report he was already extremely reckless). If you keep playing Russian Roulette, and occasionally add another bullet, eventually the game will end. There is no evidence he was going to stop until he was killed by his own decisions.
None of this takes away the tragedy of it. It's sad, and will remain so.
> unlike a metal hull, carbon fiber hulls accumulate subtle damage on compression that's hard to detect
All metals suffer from that, too. It's called fatigue damage. It bedeviled the aviation industry for a long time because there was no reliable way to detect the fatigue damage.
Eventually, an ad hoc formula was developed to calculate the fatigue damage, and then replace parts that were getting close to the limits.
That's why airliners are scrapped after something like 62,000 flight cycles.
And if you're USAF, you practically strip the aircraft to its frame every few years, inspect, repair, and reassemble it. The dangers are known and the process around it is there to deal with those dangers.
Most aircraft fleets operated by people who care will do something similar but perhaps not as extreme. In fairness to them they don't expect to fly the plane as long as USAF does (70+ years for the B-52, 50+ for many fighters).
I think you missed the thrust of OP. The submersible had instruments in it to report on the hull condition. They all were reporting it had previously experienced severe strain before the last dive, and they were designed as tripwires. If they tripped, the hull should have been considered unsafe and not used again. They were ignored.
It is a shock that they actually worked and reported the hull was unsafe before it failed. Given everything else, it's not a surprise in the slightest that they were ignored.
They used an unproven custom-designed sensor + controller system to monitor the health of the hull.
The monitoring system detected the beginning of total hull failure in the exact way they intended. They then ignored that monitoring system because hull failure would have been inconvenient.
Really that's the whole story of Stockton here. Massively motivated reasoning. Anything inconvenient was written off as wrong. A lot of normalization of deviance too as some of the written-off concerns turned out to be wrong. But not all of them.
I recently got my PPL and that's a massive risk for pilots. You fly in weather you shouldn't and get away with it for a while. Then it becomes normal. You've "proven" you can handle it. Then a situation comes along that requires more margin than you have left and you die.
Once again... The instruments reported the hull was no longer safe for use before the start of the last dive. That was well before the implosion. You keep ignoring this part to focus on how there was no engineering that would suggest that those instruments would actually give early warning. I'm halfway there with you. It is actually a surprise that they reported it was unsafe before the dive. But they did, and that makes the subsequent human failures even more egregious.
I'm not sure he had the money to make another hull. I think that's the crux of the issue, he didn't have a usable system and he didn't want to give up his ambition.
Money was a big part of the problem. The whole point of making it out of carbon fiber was to make it light and therefore cheap to operate. He could have made a long DSV with plenty of room for passengers out of metal, the Aluminaut DSV was such a craft with proven performance, but then he would have needed to buy or rent a more expensive ship to operate it with.
Yep. There are a ton of incidents described in the report which all stink of penny-pinching. Probably one of the most obvious is reusing the titanium end cap components from the first submarine; this may have played a role in the failure of the Titan, as the mating surfaces may have been damaged or incompletely cleaned when rebonding them to the new hull.
Well, I for one enjoy being able to fly in airplanes. I'm glad nobody back in the day decided that flight wasn't something most Americans should be able to do.
On the related topic, people did wonder if Rush was the right person to be leading this project and numerous people raised governmental complaints. However, mostly due to staffing issues within the government they weren't handled in any appropriate amount of time and any entity with the ability to stop him didn't.
Other than the finances of it, he was a total narcissist who refused to believe anyone else knew more about anything than he did. Even when presented with hard data he chose to ignore it and killed himself as a result.
It didn't do a lot of dives before it failed. The dive number was the number of "dives" oceangate did using any hull. Additionally most of those dives were 20 feet down in a marina for testing.
>The porthole design was poor, the carbon fiber had tons of defects, the controller, everything was cobbled together, yet it held up until it didn't.
Emphasis mine.
Everybody hammers on the controller like using a gaming controller was somehow more indicative of the unseriousness of the endeavor than, you know, the firing of the guy who said the hull was unsafe. Based on what I've read, that was one of the few authentically competent design decisions of the whole bloody thing. Why waste time and resources building, designing, and most importantly lifetime testing something that you can buy off the shelf for $30 US?
The US Navy has been using off-the-shelf game controllers for years now[0], because they work. And as a bonus, the submarine designers can be confident that if Stockton Rush or Seaman Manchild or whoever throws his controller in a fit of rage when his submarine doesn't work right, the controller will still work afterwards.
Absolutely, there were problems with the control scheme (reportedly, the motors were wired into the control board wrong, so the x- and y-axes were reversed). But that's not the fault of some usb controller communicating with the control box. That's the fault of the people working on the actually bespoke portions of the submarine.
>Why waste time and resources building, designing, and most importantly lifetime testing something that you can buy off the shelf for $30 US?
That's fine, but you would think they would buy a high quality one (like $70), use a wired one, and maybe have a spare? I think that's a lot of where the ire comes from. It's the cheapest and easiest part of the system and still they skimped out (and it's memable for gamers, given how common the experience of 'third party controller the little brother/least favored friend has to use' is). I worked on a self-funded student project making an autonomous underwater vehicle and we still used a better controller than they did (the xbox 360 controller is the obvious choice for such things. It's ubiquitously understood, trivial to interface to, reasonably priced, and pretty damn solid)
It's not just that they used a game controller, they used a super cheap crappy controller instead of something backed my a major company with millions of R&D funding or a modern device with better sensors (hall effect/TMR) better suited for controlling vehicles in something other than an arcade game.
Like, they couldn't even spring an extra ten bucks for the same controllers that Navy uses.
Is Logitech not a major company, backed by decades of experience building these things? Its not MadCatz, that's for sure. I mean, logitech is the undisputed king of low-to-mid-range joysticks, and has held that title more or less since microsoft stopped making joysticks and gamepads in 2002. Microsoft didn't make a PC-friendly controller again until 2005. They basically ceded the market during that period of time. Of course, logitech hasn't sold as many units. But they know what they're doing.
Granted, a Logitech controller not the first party controllers, and I'm prepared to believe that the Xbox people made a generally better controller, but I'm not convinced it was so much better as to be an actively bad idea to use the Logitech device. Like, once you get to the "pretty good, people won't return it" phase of controller development, its just fine tuning for gameplay performance, and there's absolutely nothing about controlling a tourist submarine that makes e.g. controller latency or even signal integrity above and beyond the baseline the bottleneck. I'd wager that the real reason they picked it likely devolved down to "what driver is our embedded controls engineer most comfortable integrating into our system?", which has a much larger impact on system safety.
I agree with a sibling that there's an argument for using a wired controller. But that's pretty much as far as that criticism goes for me, speaking as someone who writes firmware that does need to be reliably low-latency and responsive, game controllers barely even register on my radar, except that I wouldn't do it myself if I didn't have a specific use case for it.
Logitech is _so bad_. They use these crappy jittery potentiometers and then charge way too much for their plastic crap. Then it breaks within a few years
Better alternatives:
Gamepads: 8bitdo, Gamesir
Joysticks/HOTAS: VKB, Virpil, Winwing
Wheels: Moza, basically anything with direct drive
Any of the above will last _decades_ and greatly outperform a Logitech in precision, in a way that is qualitatively important to realistic vehicle control.
There's a documentary about it on Netflix and the impression I came away with is that, while there are fundamental engineering problems associated with a carbon fiber design, they could have probably overcome them in one way or another.
The problem with oceangate is that their CEO was an arrogant narcissist who thought he knew better than everyone, and if anyone stood in his way he would explode with anger at them and fire them. It was a company with absolutely no culture of safety and a cult of personality where people were punished for being honest. The CEO knew about the problems and still somehow believed, to his core, that everyone else (including hard data!) was wrong. He believed in his own infallibility so deeply that it killed him
I've heard both assertions. I tend to believe that Carbon Fiber is a fine material to use.
This submersible used untested techniques. They didn't adhere the layers together properly and apparently never bothered to X-ray the tube as that would have shown at least some of the defects. It also seems like there were other design issues with how the tube was paired to the ends.
Most importantly, the deaths were caused by negligence during operation and maintenance. They had the data showing when the hull was damaged on the previous expedition, but either never did their due diligence and analyze it or ignored the results. Even during their last expedition, they may well have avoided death if the alarms had been heeded.
EDIT: to answer the people who seem skeptical, there are companies making carbon fiber vessels that have successfully gone much deeper than those Titanic dives. We're still in the learning stages with the technology, but we'll eventually find the combinations and standards that can make it safe to use (at which point, it may become better than our current solutions). Until then, maybe we shouldn't be shoving people into damaged experimental vessels to see what happens.
The Coast Guard report section “5.6 Insufficient Understanding of Carbon Fiber Material Properties for Deep-Sea Applications” addresses your arguments.
Yes. It can be safe. The problem is that its crystalline structure can fail instantaneously without any ability to detect beforehand. In this case the sub was likely improperly manufactured and improperly stored and damaged from previous dives and from transport. The company “planned” to inspect but as no non destructive testing was possible, they didn’t bother.
There is a YouTube channel that anaylzes the core problem in depth. Compression vs. tension is really a red herring because in a closed convex structure compression somewhere is tension elsewhere. The real problem is the carbon fiber maxtrix was wapped around the epoxy filler without tension like paper mache. So it had insufficient strength and non homogeneous strength. The sub was built up like an onion. Concentric layers of carbon fiber epoxy thermoset. I think it was something like 5 layers. Anyway because the layers were not wrapped tight before curing there were ripples in the surface of each layer. Subsequent layers were applied after sanding down high spots and applying a wrap of double sided adhesive tape between each layer (no joke). So not only were the carbon fibers not pretensioned but also they were cut in hundreds of spots. This is somewhat like if one were to pour layers of reinforced concrete by throwing a bunch of loose rebar in a hole, pouring concrete over it and then cuting pieces of rebar that stuck up before applying the next layer after putting a layer of plaster over it. For carbon fiber composites and concrete to be strong tension bearing elements need to be able to bear tension. If they are loose in the matrix or cut the composite will not be strong. Thus carbon fiber was not the problem but rather its manufacturing process. Anyone who has ever done drywall joints or autobody can understand the problem. It doesn't take an engineering degree to understand that if you wreck the tensile components of your composite it will be much less strong than if the composite is laid down properly!
>I tend to believe that Carbon Fiber is a fine material to use.
For deep underwater?
Apart from the series of stupidities you go on to list, I'd love to hear your reasons as to why?
I'm a carbon f bike rider, even down to carbon spokes and I do not trust the material, knowing that pressure, or force, applied in the wrong direction will make it crack!.
As for carbon in a circle...no way.
I think it's not ideal in the same way that plastics don't belong in an automotive engine bay and concrete doesn't belong" in tension. Add a little bit of fancy chemistry or some steel and fancy math and they both work fine for cheap.
With care and engineering trickery CF in a submersible (compression) probably can work. They still managed to make a few good dives with it despite comically bad decisions in just about every key area. The manufacturing process was primitive, the QC basically nonexistent and procedures didn't make any allocations for the materials (they beat on the thing like it was made of steel). Imagine what a well funded company with experience in CF, robust QC and careful operating procedures could do.
A submersible constructed of carbon fiber went to depths that many metallic submarines and submersibles cannot.
If somebody constructs a submersible and then tests it to 5000m and finds it fails on the 200th run after exhibiting for the past 50 dives bad acoustic data. Wouldn't you think it's fine for them to take people on the same designed submersible that's only done 100th runs and still has good data?
Everything is a consumable in the long run. They didn't have data on what Titan looks like before a failure. Although in hindsight the acoustic data looks really bad, the issue really is just the specific design didn't have a known lifespan. A submserible without that defect is going to be a lot safer.
Trek 2100. The first carbon fiber bike affordable by upper middle class people.
Their trick was pre-formed carbon tubing glued to aluminum lugs. Sound familiar?
Good, because they had a massive recall because the carbon at the joinst started to chip and crack. Member of our club had to call a friend to come get him because his top tube came apart fifteen miles from town. Took em a while to replace it too. Eventually he ended up on a Serotta (Titanium with extra metalurgical tricks to make it lighter still).
I've linked this elsewhere in thread, but here's testing results from a US Navy pilot project for carbon fiber unmanned subs. It looks like this found it pretty viable.
What's the issue with CF in a circle? My bike is mainly CF (mainly just brakes and drivechain are metal) and of course that means CF wheels which I think are great (CF means that you can have deep section "aero" wheels without much of a weight penalty).
When carbon fiber rims were new we still had not transitioned to disk brakes. You had to keep an extra eye out for misaligned brake pads to make sure they weren't dragging on surfaces not meant for friction contact. Now they make more sense. But also different loads on a wheel under braking than before, but also more like a wheel under acceleration, which is torsional force on the other side of the axle and pointed the opposite direction.
You don't need to watch Netflix series. There is a transcript of entire conversation between Stockthon and David Lochridge where the former scolds the latter for taking his safety concerns outside of company and firing him:
>Not at all, because carbon fiber is better compression than tension. And that's what nobody understands. It's completely opposite of what everyone else says. Everyone's, oh, carbon fiber can't handle compression. They're full of shit, and I've proven they're full of shit. If you want to see that, you take a look at the third scale model that we tested.
Jesus Christ, I met people like him in previous jobs when I worked in Aerospace. Don't need to know nothing but a giant ego and connections to get a job managing engineers.
Carbon Fiber just isn't suited for submarine type of loads. It really doesn't like being compressed, and it tends to give you no warning before snapping.
This isn't the first carbon fiber submarine, although it is the first manned one. The US Navy tried out an unmanned model in the 80s, and got much better results- they were expecting at least 1000 successful dives before stress fatigue was an issue.
Here's a detailed report on it. Pages 32-33 has their take on material analysis, probably the most relevant to this failure
It’s the unpredictable nature of failure that’s at issue here. For unmanned subs it doesn’t matter if 10% of failures occur well below the expected lifespan but that’s a huge issue for manned subs.
I'm not even sure it's the first manned carbon fiber submersible.
Deepflight Challenger [...] is the first deep-diving sub to be constructed with a pressure hull (central tube portion) of carbon fibre composite, built by Spencer Composites for HOT. Its carbon fiber design would later influence the tube for the sub Titan,[12] which imploded...
"""
Based on testing at high pressure, the DeepFlight Challenger was determined to be suitable only for a single dive, not the repeated uses that had been planned as part of Virgin Oceanic service. As such, in 2014, Virgin Oceanic scrapped plans for the five dives project using the DeepFlight Challenger, as originally conceived, putting plans on hold until more suitable technologies are developed.
"""
Being manned is a major difference. Humans need a lot of space. Pressure grows with volume, which is cubic, but the hull grows with area. You can also submerge components in oil, which is much better at resisting pressure than air.
Pressure doesn't grow with volume. The exterior design pressure is constant. The stress on the wall scales linearly with the diameter. Making submarines bigger actually makes it easier because the buoyancy scales cubically with the volume while the weight scales linearly with the perimeter, so the larger the submarine the thicker the walls can be.
There’s several kinds of scaling involved, once the radius increases enough thicker walls are less efficient than internal bracing.
It’s impractical to build something like an Ohio class submarine that can reach the bottom of the Mariana Trench when you also want multiple internal compartments in case of damage.
Internal bracing is to resist buckling. You need it as your cylinder gets longer (as military subs tend to be), but has nothing to do with the diameter. It's also good for torsional strength, which is not really a concern for a pressure vessel but is important for a ship that's going to be in the actual ocean. But for just resisting pressure, once your diameter exceeds 20 times the wall thickness, the relationship is linear.
You can get better efficiency with multiple spherical pressure vessels joined together over a cylindrical vessel, as spherical pressure vessels better distribute the loads than cylinders. This is done in some particularly deep diving military subs, which are then surrounded by an unpressurized cylinder for hydrodynamics.
Even with a spherical sub the diameter impacts a lot of things. For example a large sphere sees significantly lower pressure across the side facing the surface than the side facing the sea floor.
At the depth of the titanic to see a 1% variation in pressure between the top most and bottom most points of a sphere, the sphere would need to be 40 meters in diameter. For context, the pressure vessels of the largest submarine in the world have a diameter of 10.9 meters. Note that pressure at a given depth varies due to things like temperature fluctuations, ocean currents, and even variation in Earth's gravity. Further, the walls of pressure vessels distribute the load - any variations of the pressure get averaged out. It's the same principle as a dome - every element of the sphere is pushing against the adjacent elements and resisting being pushed by those adjacent elements. At the size scale where this is no longer the case, you're not building a pressure vessel. If you're making a dam or a hollow column going down into water, or perhaps a massive dome on the ocean floor, you would need different equations. Even for a submarine you may be concerned with things besides pressure resistance, like collision or sea keeping, as previously stated. But from a pressure resistance standpoint the diameter to wall thickness requirement holds equally true for small exploratory subs and the largest military subs.
A sphere is a great shape for dealing with such forces but it’s just a more complicated system. Rotation can cause metal fatigue, openings get more complicated, etc.
> For context, the pressure vessels of the largest submarine in the world have a diameter of 10.9 meters.
Few subs can reach the titanic at 12,500 feet, at more common crush depths and especially non spherical geometries it’s very much worth considering. Subs often dive and surface at a significant angle.
Carbon fiber is actually a pretty good material for submarine type loads. Submarines have to balance their need for an extremely strong hull with the need for buoyancy. For a given size, to make your hull stronger, you must make your walls thicker, which makes you heavier. The only options are to make the sub bigger, increasing the internal volume, or making the hull out of something with a better strength to weight ratio, or more accurately a better strength to specific gravity ratio.
In carbon fiber composite, it's actually the epoxy which provides the compressive strength, and while it has very good compressive strength, the real advantage is its very low density. It is only just barely denser than water, so you can make your hull extremely thick with essentially no loss in buoyancy. Carbon fiber does fail catastrophically, but they could have just made the hull so thick that they were never getting anywhere near the failure point. Further, since carbon fiber is built up in plied layers, you don't have the same sorts of processing limits as with thick metal plates.
The basic concept of Titan was sound, it was just horribly horribly executed. With their flagrant violation of basic engineering and safety practices, they would have killed people no matter what they made their sub out of.
"Isn't suited" is a stretch. They still managed to make a few good dives with it despite comically bad decisions in just about every key area. Imagine what a well funded company with experience in CF, robust QC and non-laughable operating procedures could do.
It's not ideal on a first pass analysis in the same way concrete can't to shit in tension yet with a bunch of carefully placed steel and number crunching magic it works great. I think they proved that CF has the same potential. A more serious attempt could likely work in some capacity.
There's been a vibe shift. A cult of personality around an arrogant narcissist who fires people for publishing hard data when it contradicts him is apparently what a lot of people seem to want right now.
> The problem with oceangate is that their CEO was an arrogant narcissist who thought he knew better than everyone, and if anyone stood in his way he would explode with anger at them and fire them. It was a company with absolutely no culture of safety and a cult of personality where people were punished for being honest.
Sounds like someone else that's been in the news these last few months.
> The problem with oceangate is that their CEO was an arrogant narcissist who thought he knew better than everyone, and if anyone stood in his way he would explode with anger at them and fire them.
There has to be a point at which you go "fuck it" and stop working for such a guy, even if you haven't been the target of his temper. I lasted 9 months at a company that had a CEO who wasn't explosive, but toxic in so many ways. His company had a 90% staff turnover over any given 18 month period, primarily everyone outside of senior leadership. If senior leadership had stopped propping him up, and quit that company would have been dead and buried far quicker. Thankfully that company wasn't involved in anything that could endanger anyone's lives.
