The Titanic Sub was an experimental vessel built to push the boundaries of underwater exploration, that shuttled passengers to the resting site of the Titanic (ship) that rests on the ocean floor. As you are likely aware, a tragic turn of events unfolded June 2023 when the sub lost connection to the mothership (which controlled the navigation of the sub). It was later confirmed that the sub had imploded, and debris was found in the ocean.
As an engineer, I get questions about world events all the time. Many I may not be able to answer, but this one wasn’t among them. I realize that official announcements of causation have yet to occur, but the failure mode is fairly one-dimensional (and will be explained later in this article).
In this article, we delve into the workings of submarines, their reliance on engineering precision, and the potential failure modes that may have contributed to the fateful implosion of the Titanic Sub. Through an understanding of thermodynamics, structural integrity, and the complexities of underwater pressure, we shed light on the intricate balance between human exploration and the unforgiving forces of the deep sea.
Understanding Submarine Design:
Submarines are marvels of engineering, designed to operate underwater and withstand the immense pressure exerted by the depths of the ocean. They rely on a combination of buoyancy control, propulsion, navigation, and life support systems to enable exploration, defense, and research in the depths of the oceans. Let’s examine the key components and design principles that make submarines functional and safe.
1. Hull Design and Construction:
The hull is the outermost structure of a submarine, responsible for maintaining its integrity. It is typically constructed using high-strength steel or advanced composite materials to withstand the crushing pressure at great depths. The hull is carefully designed to distribute the external pressure evenly, ensuring structural integrity throughout the submarine’s operations. Fluid pressure exerts its force in all directions, at all times, so you tend to see most designs spherical in nature. As you may know, the arch is one of the strongest load-carrying arrangements, and this shape helps use the water pressures to resist other water pressures. The curved design helps distribute external pressures more evenly, reducing stress concentrations and enhancing the submarine’s ability to withstand the high water pressures at greater depths. It also provides a streamlined shape to minimize drag (resistance of the water on forward movement).
2. Pressure Vessels:
Within the hull, pressure vessels, also known as compartments, are utilized to house critical components and provide habitable spaces for the crew. These compartments are designed to withstand the internal pressure of the submarine and prevent water intrusion. They are typically reinforced and sealed to maintain a controlled environment. It is the pressure maintenance within the sub that keeps it from crushing, to resist the immense pressures outside the submarine.
To help illustrate, the pressure of the water below the surface accounts for all of the weight of the water that is overlying it. So water 1 foot below the surface is a lot less pressure than water at 7 feet below the surface. You likely feel this difference when you swim in the deep end of a swimming pool.
Now at a depth of 12,500 feet, or the depth of the Titanic grave site, the pressure is roughly 6,000 pounds per square inch. So every single 1 inch by 1 inch square sees 6,000 pounds of force. That is nearly 400 times higher than nearer to the surface.
3. Ballast Tanks and Buoyancy Control:
Submarines employ ballast tanks that can be flooded or emptied to control buoyancy. By adjusting the amount of water in the ballast tanks, the submarine can submerge or surface. This system ensures stability and allows the submarine to navigate at different depths.
It is unclear if this sub had these to control buoyancy, as many reports include statements that “weights” are dropped to allow the sub to return to the surface. We also note that this sub was not able to control it’s own buoyancy, as the controls were conducted from a surface vessel.
4. Life Support, Air Locks, Redundant Safety Systems:
This sub didn’t have any of these. People paid $250,000 per person to ride an un-proven and un-inspected vessel to extreme depths with no redundancy systems for any operation. No air locks to keep the vessel from failing upon any puncture or impact, and no life boat or other support mechanisms.
Potential Failure Modes and Implosion:
While submarines are designed to withstand extreme conditions, they are not impervious to failures. Several potential failure modes could have resulted in the implosion of the Titanic sub. Admittedly, this sub was exponentially more susceptible to failure than world-class submarines made today. Let’s explore some of them:
1. Hull Puncture:
The impact that punctured the hull of the Titanic sub likely caused the implosion. The hull’s integrity is crucial for withstanding external pressure, and a breach could have initiated catastrophic failure. If the puncture was enough to deplete the pressure faster than it could be replenished, the resulting imbalance in pressure could have led to the collapse of the hull.
There were reports of the ship having lost connection to the mother ship. In this time, it could have floated or drove right into anything. An impact to the hull would be enough for this lightweight structure to succumb to the great pressures of the ocean.
It is also possible that fatigue failure kicked in. Fatigue failure is a stress on a component due to repeated use or distortion. Think of it like when you want to get rid of an old credit card and have no scissors that can get through the plastic. You bend it back and forth, over and over. One bend and it’s fine. But you keep bending back and forth enough and it fails with much lighter pressure. This is fatigue failure.
2. Material or Manufacturing Defects:
In rare instances, material or manufacturing defects can compromise the integrity of the submarine’s structure. Flaws in the construction or use of inferior materials can weaken the hull, making it susceptible to failure under pressure. Quality control during construction is crucial to mitigate such risks.
This sub did successfully complete missions prior to this incident, so while these failures may have occurred, you would think that signs or symptoms of failure would have been evident prior.
3. Inadequate Pressure Equalization:
Submarines utilize various systems to equalize pressure between the interior and exterior environments. If these systems fail or are inadequately designed, significant pressure differentials can develop. Such pressure differentials, especially during deep dives, could overwhelm the structural integrity of the submarine and lead to implosion.
The sub may have had a failed valve or pressure equalization process. The lack of the sub’s ability to control its pressure would certainly lead to it’s implosion.
4. Improper Ballast Control:
Effective control of ballast tanks is vital for maintaining stability and buoyancy. If there are malfunctions or errors in the ballast control system, the submarine may experience uncontrolled changes in depth. Rapid ascent or descent can subject the hull to extreme pressure differentials, potentially causing structural failure.
When you go down or up in the ocean, you have to do it in stages. This allows adjustment to the pressure differentials that you get along the way. If the ship went up or down too fast, the result could have led to an under/over pressurization of the sub. As you guessed, this could lead to failure.
Submarines represent the pinnacle of engineering achievements, enabling us to explore the ocean’s depths. However, they are complex machines that demand meticulous design, construction, and maintenance to ensure their safety. The implosion of the Titanic sub highlights the importance of understanding potential failure modes and implementing robust engineering practices.