On the 19th of June the oceangate submersible began its descent to the Titanic’s fractured
remains here, in the north western atlantic.
With a descent rate of 55 metres per minute it would take the submersible 70 minutes to
reach its destination.
With each passing minute the equivalent of 5.3 atmospheres of pressure would be added
to the subs hull.
By the time it reached its target depth the weight of 366 of earth’s atmospheres would
be attempting to crush it.
Applied to just an area a little larger than an A3 piece of paper, that’s equivalent
to the thrust of a Saturn V F1 engine.
Pressing in from all directions.
An hour and 45 minutes into the dive.
At the bottom of the Ocean.
3800 metres down.
With this immense pressure bearing down on its hull.
The oceangate submersible lost contact with the surface.
We now know the submersible imploded, a sudden catastrophic collapse.
A tragic accident, however any composite material engineer could have predicted this failure,
and they did.
I worked as a composite design engineer and completed my master’s thesis in composite
failure prediction.
So, let’s dive into the questionable engineering decisions that Oceangate made that led to
a tragic accident.
With that pressure comes some extreme design challenges.
Oceangate’s Titan submersible consists of two titanium end caps, one with a large acrylic
window, joined to a filament wound carbon fiber reinforced epoxy hull.
[REF]
Inside the submersible is pretty barebone.
Some screens that are fed data from cameras from the outside.
The four electric thrusters are controlled with, from what I can tell, a third party
gamecube controller.
Many people are focusing on this part of the design, but that’s the least of my concerns.
We will be focusing on one design aspect of this submersible, the composite hull.
Carbon fibre composites aren’t really known for their compressive strength.
They work best in tension.
Great for airplanes that are pressurised from the inside.
Where the pressure inside the fuselage works to expand the circular cross section, putting
the fibres in tension.
For a submarine, the pressure will work to compress the hull, placing the fibres primarily
under compression.
This immediately set off alarm bells in my mind when I heard of the missing submarine,
so I began digging into their justification for using the material.
Oceangate chose this carbon fibre composite primarily to benefit from its natural buoyancy.
These types of subs actually want to be as close to neutrally buoyant as possible.
Meaning the weight of water they displace weighs about the same as the vehicle itself.
Minimising the energy needed to rise or sink in the water.
This means to surface in an emergency they don’t need power, they just drop ballasts
that make them positively buoyant and they just float to the surface.
The carbon fibre composite can be lighter and thus helps achieve this neutral buoyancy
target.
Typically submarine hulls are made from steel or more recently titanium, but in order to
achieve the desired buoyancy they need foam outer layers.
OceanGates CEO Stockton Rush, who was inside the submersible stated that they wanted to
skip this foam layer because it added to costs.
That isn’t necessarily an evil thing if the composite is up for the job.
This is where things get iffy, oceangate had no idea whether it was up to the task or not,
and we know this because they admit in their own blog post justifying their decision to
not test their vehicle with a regulatory body.
[REF].
The now removed blog entry read:
Most major marine operators require that chartered vessels are “classed” by an independent
group Classing assures ship owners, insurers, and
regulators that vessels are designed, constructed and inspected to accepted standards.
Classing may be effective at filtering out unsatisfactory designers and builders, but
the established standards do little to weed out subpar vessel operators The vast majority
of marine (and aviation) accidents are a result of operator error, not mechanical failure.
As a result, simply focusing on classing the vessel does not address the operational risks.
Now, I would have thought this wouldn’t need pointing out, but the fact this glaring
red flag has been written on their own website for everyone to see, and several extremely
wealthy and successful people didn’t seem to think it was an issue seems to suggest
otherwise.
Perhaps most submarine failures occur due to operator error precisely because they have
undergone rigorous testing and certification.
The comparison to aviation is also just a wild can of worms that we have very recent
catastrophic accidents to compare to, where manufacturers willfully circumvented regulatory
procedures.
These aren’t procedures created as some kind of unnecessary inconvenience to inventors.
They are very useful guidelines and testing procedures to prove you have not missed some
catastrophic failure mode in your design, and that’s exactly what happened.
One failure mode is unique to composite materials in deep sea applications.
Some of the first evidence we got for it was glass fibre reinforced deep sea piping.
It’s called snap buckling, or delamination coupled buckling failure mode.
For thin walled pressure vessels the failure mode is simply buckling, where the pressure
simply caves the entire wall in, but here, because the wall thickness is so large to
deal with the immense pressure of the deep sea the failure mode gets more complicated.
This failure mode is characterised by delamination of the internal layer of the pressure vessel,
basically the inside of the pressure vessel suddenly peels away from the rest of the wall,
leading to catastrophic failure of the overall structure.
The exact mechanisms of the failure mode are not entirely well understood, as stated in
this 2022 research paper titled “A Review on Structural Failure of Composite Pressure
Hulls in Deep Sea”.
[REF] It states, in its conclusion
“investigations on this subject have remained at theoretical level.
There is still very little research in this area in recent years.”
So, I am assuming whoever engineered this pressure vessel did at least the same level
of research as a YouTuber who wrote a script on the subject in two days.
They must have at least been aware of this problem.
A failure mode like this is going to be exacerbated by gradual damage incurred through cyclical
stresses, like those experienced when diving to the depths of 4000 metres and resurfacing
again.
They have done that at least 50 times with this vessel, without ever fatigue testing
it.
Per their own admission they did not undergo industry standard classifications, but they
did do their own classification test.
One test, stated on that blog post once again.
“A licensed marine surveyor will witness a successful dive to 4000 metres, inspect
the vessel before and after the dive, and provide a Statement of Fact attesting to the
completion of the dive test plan.”
That is simply not adequate.
Anything undergoing repeated stress cycles like this needs to be fatigue tested.
Like the test airplane manufacturers do on wings where they flex the plane's wings thousands
of times on the ground.
They designed this thing essentially with computer modelling with no real world testing.
Composite materials are incredibly difficult to model in computer software.
Composite materials are far more complicated than homogeneous materials like steel, where
the material properties are the same in all directions and in all regions of the material.
Composites are composed of fibre bound together by a matrix material like epoxy.
If we were to zoom into a small cross section of this, we may see something like this.
Some fibres, some of them could be touching without any matrix between them, some could
be spaced further apart, and there can also be empty voids that the epoxy didn’t manage
to fill.
We can simulate a small section like this independently to help analyse some failure
modes, such as delamination.
However if we want to zoom out and test a larger section we often need to average the
material properties in some way or else the simulation will take too long to run.
My own master thesis tried to combine the two by embedding a fibre and matrix cell within
an averaged composite material.
There are specialised softwares that can model different fibre orientations, but they are
still very much an estimation.
You need to back this up with physical testing.
Something OceanGate didn’t do.
There are more signs of incompetent use of composites.
For a critical structure like this, I would very much recommend curing it in an autoclave.
That’s basically a pressurised oven that helps push those voids I mentioned earlier
out of the epoxy resin.
Autoclaves are expensive, and can be difficult to find ones large enough to fit something
like this, but it’s nice to not have air bubbles in a pressure vessel keeping you alive.
However, it wasn’t used for this pressure vessel.
It was simply bagged and cured, a cheaper alternative.
Spencer Composites was commissioned to make the composite hull and their CEO was interviewed
back in 2017 in a compositesworld article.
He seems very aware of the immense design challenge he was handed, and he does mention
that the porosity of the cured pressure vessel was assessed to be less than <1%.
“Less than 1% voids” doesn’t exactly inspire confidence.
Is it 0.99% or 0.0001% porosity?
That’s exactly the type of defect that’s going to increase the risk of snap buckling
as voids can be propagation sites for delamination.
The blog post goes on to dismiss classification tests as unsuitable for innovative designs,
which is just complete narcissistic nonsense.
This isn’t innovative.
They have just made the pressure vessel from a carbon fibre composite, using known manufacturing
practices, and started charging rich people 250,000 dollars to risk their lives in it.
Innovation would be creating that pressure vessel and testing it.
Figuring out the causes of snap buckling and advancing material science for all mankind.
This is profiteering, not innovation.
To eliminate all doubt that this company has willfully ignored standard safety practices.
This court case from 2018 was brought against oceangate by a former employee who was fired
shortly after raising concerns about the composite hull.
Stating not enough was done to check for delaminations and voids.
Oceangate argued that the technology to check for voids and delaminations in a composite
this thick did not exist, and instead they would use their acoustic monitoring system,
which essentially listens for the sounds of fracture to predict failure.
But this is what a carbon fibre composite fracture curve looks like.
It’s a cliff edge.
Sudden catastrophic collapse.
An acoustic monitoring system like this is akin to setting up a camera to warn you thunder
is coming.
You will see the lighting before the thunder, but the time between them is minimal.
Pure safety theatre.
It gets even worse.
On one test dive in the Bahamas, a submersible expert could hear the cracking with his own
ears and warned Stockton Rush that it was a sign of damage accumulating.
Stockton, once again, chose to ignore an expert's advice.
So this acoustic monitoring system was purely for marketing purposes.
To give customers, who don’t have the engineering background to see through it, a false sense
of security.
I would attribute this to malice and greed, but Stockton Rush chose to pilot this death
trap himself.
As the Hanlon’s Razor goes: Never attribute to malice that which can be
attributed to stupidity.
There is this growing trend in engineering of moving fast and breaking stuff.
Mostly driven by one overconfident CEO who has, to be fair to him, succeeded in revolutionising
an entire industry with that ethos.
That incriminating blog post even mentions SpaceX, Blue Origin and Virgin Galactic as
bastions of innovation for this move fast and break things mantra.
Virgin Galactic too have blood on their hands, with their 2014 in-flight break up, which
was attributed to inadequate design safeguards and poor pilot training, along with a lack
of oversight from regulatory authorities.
This attitude is dangerous, and this won’t be the last story of wealthy narcissistic
CEO’s putting lives at risk.
When a doctor is negligent to the safety of their patients, they are liable for malpractice,
but the impact their incompetence has affects one patient, when an engineer neglects their
responsibilities it can affect hundreds, thousands, maybe even millions of people.
We need more people like David Lockridge, the employee who was fired for raising concerns
over safety.
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