In this blog post, we will examine the causes of the Sewol ferry sinking from a naval architecture perspective—focusing on stability, ballast water, ship structure, and operational management—and explore the lessons learned from the accident.

Overview of the Incident

On April 16, 2014, the passenger ferry Sewol, en route from Incheon to Jeju, sank in waters near Jindo County, South Jeolla Province. Of the 476 people on board, 304 died or went missing. The fact that a significant number of the victims were high school students on a field trip left South Korean society in a state of shock and deep sorrow.
Following the accident, various causes were investigated, including the inappropriate response of the captain and crew, the shipping company’s inadequate safety management, and problems during the rescue operation. This article examines, from a naval engineering perspective, how the ship’s inherent stability and operational management—particularly its stability and ballast water management—affected the accident.

Stability and Its Importance

The 21st century is an era in which the importance of maritime logistics and maritime transportation has grown even further, and ship safety is the most critical factor. International regulatory bodies, including the International Maritime Organization (IMO), and classification societies have established strict standards regarding ship stability and continuously manage and oversee them.
Stability refers to a ship’s ability to return to its original attitude when tilted by external forces; this force is called the restoring force.
In reality, ships do not always sail on calm seas; they are subjected to various external forces such as waves, wind, currents, and turning maneuvers. For a ship to safely maintain its balance under these conditions, the relationship between its center of gravity and center of buoyancy must be properly maintained. If stability is insufficient, the risk of the ship listing sharply or capsizing even under minor external forces increases significantly.

The Role and Adjustment of Ballast Water

Ballast water refers to seawater stored in ballast tanks beneath the hull to lower the ship’s center of gravity and maintain lateral balance. The lower the center of gravity, the greater the ship’s stability—a principle similar to that of a roly-poly toy, which does not tip over easily.
Furthermore, since a ship’s center of gravity constantly changes depending on cargo load or the number of passengers, ballast must be adjusted to suit the operating conditions. In particular, on ships where the loading conditions frequently change—such as container ships or passenger ships—seawater is taken into or discharged from ballast tanks to maintain the center of gravity and lateral balance.
Since the volume and distribution of ballast water directly affect a ship’s stability, they are strictly managed in accordance with international regulations and safety standards. Furthermore, modern ships not only manage ballast water but also comply with ballast water treatment standards designed to protect marine ecosystems, as mandated by the International Convention on Ballast Water Management (BWM Convention).

Analysis of the Sewol Ferry Case: Causes of Loss of Stability

According to the official investigation findings and the court’s ruling on the Sewol Ferry accident, the cause of the accident was not a single factor but rather the result of multiple interrelated issues.
After being imported from Japan, the Sewol Ferry underwent expansion and remodeling, during which additional passenger cabins were added, increasing the weight on the upper part of the hull and consequently raising the center of gravity. Following these structural changes, the vessel’s stability decreased compared to before, making it necessary to carry more ballast water to compensate.
However, on the day of the accident, the ship departed with less ballast water than the recommended level. Furthermore, the investigation revealed that vehicles and cargo were loaded in excess of permitted limits, and that some cargo was not sufficiently secured.
Before departure, it is standard practice to verify that the vessel does not exceed its maximum load line. The load line indicates the extent to which the vessel is submerged in water, and the maximum load line represents the upper limit of what can be safely loaded. However, the vessel’s safety is not guaranteed simply because the load line is within normal limits. Sufficient stability can only be ensured when factors such as cargo weight distribution, center of gravity, and ballast water management are also properly managed.
At the time of the accident, the Sewol made a sudden course change in waters near Jindo, causing the hull to list significantly to one side. Subsequently, vehicles and cargo that had not been adequately secured shifted to one side, causing the center of gravity to shift abruptly and further worsening the ship’s already reduced stability. Ultimately, the ship was unable to recover its posture on its own, tilted sharply, and capsized.
In other words, it is assessed that the accident occurred due to a combination of factors: reduced stability resulting from structural modifications, insufficient ballast water, overloading, inadequate cargo securing, and a sudden change in course.

How was stability lost?

Under normal conditions, the center of gravity is maintained at a sufficiently low level, so even if the ship heels to a certain angle, restorative forces allow it to return to its original attitude.
Conversely, when the center of gravity is raised due to structural modifications, combined with insufficient ballast water and excessive cargo loading, stability is significantly reduced. Under these conditions, a sudden change in course can cause the hull to list sharply; if cargo that is not sufficiently secured shifts to one side during this process, the center of gravity shifts further. Ultimately, the restoring force becomes insufficient to right the hull, and the vessel may capsize without regaining its balance.

Diagnosis of Causes and Lessons Learned

The Sewol Ferry accident is regarded as a classic example of a man-made disaster resulting from a combination of regulatory violations and failures in safety management. After the structural modifications, necessary safety measures were not adequately maintained; this, combined with overloading, insufficient ballast water, inadequate cargo securing, and poor operational judgment, significantly reduced the vessel’s safety margin. Furthermore, the scale of the damage was exacerbated by the failure to respond appropriately after the accident occurred.
Safety must take precedence over any economic interest. In ship operations, international safety standards and procedures must be strictly adhered to, and regulations regarding stability management, cargo loading standards, ballast water management, and navigation must be rigorously followed. Furthermore, only when all stakeholders practice a safety culture that prioritizes human life above all else can we prevent such tragedies from recurring.