The fundamental engineering flaws of the Titan Submersible

On June 18, 2023, the Titan submersible made headlines when the expedition to visit the wreck of the Titanic ended in tragedy. In the North Atlantic Ocean, 3,346 metres below sea-level, the underwater vessel catastrophically imploded along with its five passengers. Two years on, this article deep dives into the key points of failure in engineering and reflects on what we can learn from the fatal incident. 

The Titanic and OceanGate’s mission

The Titanic wreck lies around 3800 metres below sea level in the North Atlantic Ocean, approximately 370 miles off the coast of Newfoundland, Canada. Since the wreckage was finally discovered in September 1985, over seven decades after the boat sank from an iceberg collision on the 15th of April 1912, less than 250 people have personally viewed the wreckage. Despite many discussions to raise the wreckage back to the surface, the complete Titanic structure has become too fragile after over a century underwater and will likely disintegrate completely over the next few decades. Hence, viewing the Titanic in person is only possible with an underwater vessel, a feat which has been achieved successfully since 1998 by a range of companies seating historians, oceanographers, and paying tourists.

The Titan submersible is one such vessel developed by OceanGate Expeditions. Titan has been attempting dives to the Titanic wreck since 2017 and was first successful in 2021, when it went on to complete 13 successful dives. According to the passenger liability waiver however, this was only 13 out of 90 attempted dives (a 14% success rate), as a result of communication signal failures, structural concerns, strong currents, poor visibility, or logistical issues. On the many failed attempts, the mission was either cancelled or aborted before the Titan reached the depth of the Titanic wreck. Despite concerns raised by engineers, poor success rates in testing and simulation, as well as previous instances of the Titan spiralling out of control, OceanGate continued with their first planned dive of 2023, leading to its catastrophic implosion that claimed five lives. The Titan is the first fatality of a submersible dive to the Titanic.

What went wrong: structural design

When designing an underwater vessel to reach a certain depth, the body of the vessel called the hull, would need to be capable of withstanding an immense amount of pressure. For 10 metres of depth, the pressure on the submersible’s hull increases by one atmosphere (1 bar or 101kPa). To reach the wreck of the Titanic 3800 metres underwater would require the hull to withstand the pressure of over 38 MPa (see Figure 1). For perspective, this is around 380 times the pressure we feel on the surface and about 200 times the pressure of a standard car tyre. Over one square inch, this equates to nearly 2500kg. To withstand such high hydrostatic pressure, a submersible hull is normally constructed with high-strength steel and titanium alloys in a simple spherical, elliptical, or cylindrical shell.

At this point we discover some of the key points of failure in the Titan.

The Titan’s hull was made from Carbon Fibre Reinforced Plastic (CFRP), i.e., multiple layers of carbon fibre mixed with polymers. Carbon fibre is a high-tech and extremely desirable material for its tensile strength, strength-to-weight ratio, high chemical resistance, and temperature tolerance. The material has proven itself since the 1960’s in the aerospace, military, and motorsport industries, however the Titan was the first case of using carbon fibre for a crewed submersible. 

At first glance, the use of a carbon fibre hull suggests the advantage of significantly reducing the vessel's weight (50-75% lighter than titanium) while maintaining tensile strength, which will allow for a greater natural buoyancy. Without the need for added buoyancy systems, the hull would be able to hold space for more passengers at one time. As carbon fibre is cheaper than titanium and passengers pay $250,000 a seat, carbon fibre may appear to be a better business plan.

However, although carbon fibre performs extremely well under tension loads, it has no resistance to compression loads (as with any fibre) unless it is infused with a polymer to hold the fibres together (see Figure 2). The polymer in the CFRP holding the fibres in alignment is what allows the material to resist compressive loads without bending by distributing the forces to all the fibres in the structure. This means the material is an isotropic: it is much stronger in the direction of the fibres than against (the same way wood is stronger along the grain). Therefore, individual layers of the CFRP must be oriented strategically to ensure the structure can withstand an expected load in all directions. A submersible hull intending to reach the ocean floor must withstand a tremendous compressive load, much higher than carbon fibre is typically optimised for in the aviation and automotive racing industries, and carbon fibre under such high compressive load is currently an under-researched field. Although it is likely possible for carbon fibre to be used in deep-sea vessels in the future, it would require rigorous testing and intensive research which was not done by OceanGate. Despite this, the Titan had apparently attempted 90 dives since 2017 and the repeated cycling of the carbon fibre composite at a high percentage of its yield strength would have made the vessel especially vulnerable to any defects reaching a critical level.

Upon simple inspection, the Titan also raises other immediate structural concerns. Submersible hulls are usually spherical or slightly elliptical, which would allow the vessel to receive an equal amount of pressure at every point. The unique tube-shape of the Titan’s hull (see cover image) would not equally distribute pressure, and this issue was ‘addressed’ with the use of separate end-caps. The joints that attach the end-caps to the rest of the hull only introduced further structural weaknesses, which made the vessel especially vulnerable to collapsing from micro-cracks. 

The Titan’s glass viewpoint was another structurally unsound feature [Figure 3]. David Lochridge, the former director of OceanGate’s marine operations between 2015 and 2018 who was fired for raising concerns about the submersible’s safety features, claimed the company that made the material only certified its use down to 1300m (falling over 2000 metres short of the Titanic’s depth). The immense forces on materials without the properties to withstand the compressive pressure made the Titan’s failure inevitable.

Cutting corners in the interest of business

The foundation of the implosion’s cause was OceanGate’s insistence on cutting corners in Titan’s design to save time and money. 

The Titan was not certified for deep-sea diving by any regulatory boards and instead asked passengers to sign a waiver stating the Titan was ‘experimental’. As underwater vessels operate in international waters, there is no single official organisation to ensure ship safety standards, and it is not essential to have a vessel certified. However, many companies choose to have their ships assessed and certified by one of several organisations. According to The Marine Technology Society submarine committee, there are only 10 marine vessels capable of reaching Titanic level depths, all of which are certified except for the Titan. According to a blog post on the company website, OceanGate claimed the way that the Titan had been designed fell outside the accepted system - but it “does not mean that OceanGate does not meet standards where they apply”. The post continued that classification agencies “slowed down innovation… bringing an outside entity up to speed on every innovation before it is put into real-world testing is anathema to rapid innovation”.

According to former engineers and consultants at OceanGate, the Titan’s pressure hull also did not undergo extensive full-depth pressure testing, as is standard for an underwater vessel. Carbon fibre - the primary material of the Titan’s hull - is extremely unpredictable under high compressive loads, and currently has no real way to measure fatigue. This makes it an unreliable and dangerous material to be used for deep-sea dives. OceanGate CEO Stockton Rush, who was a passenger on the Titan during its last fatal dive in 2023, described the glue holding the submersible’s structure together as “pretty simple” in a 2018 video, admitting “if we mess it up, there’s not a lot of room for recovery”. Having attempted 90 dives with a 14% success rate since 2017, it was inevitable that micro-cracks in the Titan from repeated dives, if not for the extremely sudden failure modes of carbon fibre composites, would result in the vessel's instantaneous implosion.

On the 15th of July 2022 (dive 80), Titan experienced a "loud acoustic event" likely form the hull’s carbon fibre delaminating, which was heard by the passengers onboard and picked up by Titan's real-time monitoring system (RTM). Data from the RTM later revealed that the hull had permanently shifted following this event. Continued use of the Titan beyond this event without further testing of the carbon fibre - because the hull was ‘too thick’ - prevented micro-cracks and air bubbles in the epoxy resin from being discovered until it was too late.

Another fundamental flaw lies in the Titan’s sole means of control being a Bluetooth gaming controller. While this is not an uncommon practice, especially in the case of allowing tourists to try controlling the vessel once it has reached its location, it is essential that there are robust secondary and even tertiary controls that are of a much higher standard. The over-reliance on wireless and touch-screen control, particularly one operating on Bluetooth which is highly sensitive to interference, was a dangerous and risky design choice. Although it was unlikely to have caused the implosion on its own, cutting corners in the electronics and controls of a vessel that needs to be operated in dangerous locations is irresponsible and unsafe.

Submersibles operating at extreme depths require robust fail-safes, including emergency flotation systems and locator beacons. Again, OceanGate cut corners in developing Titan’s emergency recovery systems, using very basic methods and off-the-shelf equipment. In the event of catastrophic failure, the absence of autonomous emergency measures is fatal. With the extent of damage and poor design to the vessel’s carbon fibre hull, it was unlikely that even the most advanced emergency systems could prevent the magnitude of the implosion. Still, the carelessness displayed in almost every aspect of the submersible’s design was ultimately the cause of the fatal Titan tragedy. 

Conclusion

In a 2019 interview, OceanGate’s former CEO Stockton Rush said:

In the world of engineering, shortcuts can be catastrophic. Whilst risk-taking is undeniably essential to support innovation, Titan’s fatal tragedy was entirely preventable and unnecessary if the proper risk management techniques were employed. OceanGate had the potential to revolutionise the use of carbon fibre in deep-sea industries but consistently cutting corners and not investing in the required real-world testing, as well as the arrogance to ignore expert warnings, is what ultimately led to Titan’s story fatefully echoing the overconfidence of Titanic’s “she is unsinkable!”.

Whilst regulations on submersibles tighten and research into carbon fibre is increased, it is important to take the fundamental cause of the tragic implosion as a wake-up call.

Assumptions are deadly: trust the science, invest in the proper research, test every bolt, and never underestimate the ocean’s relentless power.

Written by Varuna Ganeshamoorthy

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