What we know about the man-made Sewol ferry disaster, 10 years and 3 investigations later

Posted on : 2024-04-04 17:42 KST Modified on : 2024-04-04 17:42 KST
While no single cause has been found to be conclusive, investigations have shown that putting profits over safety was a contributing factor to the sinking of the ferry, which claimed over 300 lives
People gaze at the body of the MV Sewol ferry after it was recovered on March 23, 2017, and brought to a port in Mokpo. (Kim Bong-gyu/The Hankyoreh)
People gaze at the body of the MV Sewol ferry after it was recovered on March 23, 2017, and brought to a port in Mokpo. (Kim Bong-gyu/The Hankyoreh)

The 10th anniversary of the Sewol ferry sinking is fast approaching. Despite the Sewol having been brought back on land and subjected to three different investigations, the South Korean public still has not learned the full truth behind the tragedy.

This is not to say that we haven’t found some things out. The hopes of people taking the commemorative yellow ribbon to heart have been a driving force in piecing together many bits of truth over the past decade.

The Hankyoreh has compiled information that has come to light in the intervening years. Its sources include the investigation records and findings of the Special Investigation Commission on the April 16 Sewol Ferry Disaster (active from March 2015 to September 2016), the investigative panel for the Sewol’s hull (March 2017 to August 2018), and the Special Investigation Commission on Social Disasters (December 2018 to September 2022), along with the Truth Foundation’s recently published “The Sewol: Rewriting Records of That Day.”
The big question: Why the sudden turn?

The biggest focus of interest in investigations of the Sewol ferry tragedy has concerned the reasons behind the sinking. One reason the search for the cause has been confounded for so long has to do with the sudden turn that the vessel took, causing it to list heavily to one side.

In an experiment with a model vessel conducted by the Korea Research Institute of Ships and Ocean Engineering shortly after the sinking, it was found that the sudden right J-shaped turn made by the ferry would not have occurred without either a fatal steering error or a steering mechanism malfunction. If there has been one big question since the start of the investigation, it has been why the sharp turn happened in the first place.

Various hypotheses have been floated, including speculation about a possible collision with a submarine, but even those have been inadequate to explain the turn. Three different investigations by the aforementioned special commissions failed to come up with any single conclusion on why the ship went down.

Currently, there are three main hypotheses on the cause behind the Sewol’s sinking.

One is that the ferry ran aground on a reef or other obstacle. Another is that it was sunk by a collision with a submarine or other outside force. A third attributes the sinking to internal causes including engine failure and a lack of correction capabilities to maintain balance.

In a general report, the Special Investigation Commission on Social Disasters, which concluded its activities in September 2022, wrote that the “possibility of [an engine failure] causing the Sewol’s rapid right turn and listing is very low.”

“While [the external cause hypothesis] cannot be ruled out as a possibility, we have not arrived at a point where we can rule out other possibilities as well,” it said, indicating that it had failed to reach any definite conclusion.

In June 2022, the Society of Naval Architects Korea gave its official opinion to the Social Disasters Commission. The report stated, “The hypotheses of the ferry hitting a submerged rock or suffering an external blow are technically unlikely. The cause of the sinking is likely internal.” 

To get an objective understanding of the potential causes of the sinking, the Social Disasters Commission outsourced investigative work to the Maritime Research Institute Netherlands, or MARIN. MARIN’s report states that its model tests and simulations revealed “the hypothesis of an external force that caused such high values of rate of turn was rejected,” making it likely that the ferry capsized due to internal factors. 

MARIN concluded that the Sewol ferry likely heeled and then capsized due to the low initial transverse stability (GM), rudder excursion, shifting of cargo that had not been properly secured, and a sudden sharp turn.

The truth about Sewol surfaces

The theory that the sinking was based on internal factors is based on the idea that steering capacity was compromised for a vessel whose stability was already low. 

When changing directions, normally the captain turns the wheel less than 5 degrees. The wheel controls the angle of the rudder, which determines the direction of the vessel’s trajectory. The path taken by the Sewol, however, deviates from normal patterns. 

The sharp turn taken by the Sewol ferry, which already lacked stability, would have required the captain to turn the wheel at a big angle. This could happen if the steering mechanism was compromised. The Sewol rudder’s maximum turning angle was 35 degrees, but this could go up to 37 if the steering mechanism was broken.

South Korean courts have acknowledged the possibility of the vessels’ steering mechanism being compromised. On April 28, 2015, the Gwangju High Court pronounced Sewol’s first mate and helmsman as not guilty of professional negligence.

“During the Sewol’s construction, the helm’s steering capacity on the starboard was tested at a maximum of 35 degrees, which is similar to the degree of direction change that the vessel took right before its capsizing. Evidence also supports the theory that the solenoid valve had become jammed. A thorough inspection of the vessel after it has been recovered from the ocean floor will reveal a more accurate picture of the vessel’s malfunctions,” the court declared.

The solenoid valve is involved in moving the vessel’s rudder. The rudder is moved by oil pressure, but if the solenoid valve is broken, the oil pressure cannot be controlled, which could result in the rudder moving to its maximum angle even at the slightest turn of the helm.

On March 23, 2017, a total of 1,073 days after the Sewol sank, the vessel was recovered from the ocean floor. There was an opportunity to inspect the vessel to reveal a more accurate picture of potential malfunctions or flaws in design and construction. The panel investigating Sewol’s hull confirmed that the solenoid valve was clogged and that a crucial pin was jammed. In such a condition, even a slight turning of the ship’s wheel will result in the rudder turning to its maximum angle of 37 degrees. 

MARIN constructed a model of the Sewol vessel and tested it in a large tank. Its tests revealed that when the rudder veers sharply while the vessel’s stability is low, it results in a similar path actually taken by the Sewol right before the accident.

Controversy surrounding the vessel’s compromised steering capacity

There are flaws, however, in the claim that internal factors led to the tragedy. Footage taken from rescue vessels after the Sewol overturned revealed that the rudder was turned at 8 degrees to the port side (left), not starboard (right). Within the Sewol hull investigation panel, some asserted that the solenoid valve jamming could not be the cause of the accident. This is why the commission’s comprehensive report included both internal and external factors as potential causes of the sinking.

Yet even in the scenario where internal factors caused the accident, it’s not impossible for the rudder to have turned 8 degrees to the port side. The hull panel’s report states that the Sewol has two steering pumps, each one controlling two solenoid valves. The solenoid valve of Pump No. 2 was the one that was jammed. 

The Sewol as it sits in Mokpo. Its rudder is pointed 23 degrees right. (Yonhap)
The Sewol as it sits in Mokpo. Its rudder is pointed 23 degrees right. (Yonhap)

At the time of the accident, the helmsman said he had sharply turned the wheel to the left as soon as the vessel veered right, but the vessel did not respond. At this point, Park Han-gyeol, the ship’s third mate, who was standing near the port-side door of the ship’s bridge (pilothouse), pressed a button to stop Pump No. 2. At this point, the jammed solenoid valve’s impact was neutralized. Pump No. 1, which was still functional, could have then responded to the wheel and turned the rudder to the port side. This is another possible scenario.

Park has testified that the vessel sounded an alert that its steering mechanism was compromised. Park then attempted to correct the malfunction but mistakenly pressed the button that shut down the steering pump. While it’s impossible to verify whether Park disabled Pump No. 1 or 2, his testimony could explain why the rudder was turned to the port side at eight degrees.

No single cause behind the tragedy

Many waited for a clear and concise explanation that would reveal a singular cause behind the tragedy. Yet there is no single cause for a tragedy that takes the lives of 304 people. Although there are varying opinions regarding the causes behind the sinking, the general consensus is that the vessel had low stability, and its capacity for steering and stopping was compromised, which accelerated its tilt. 

Chonghaejin Marine acquired the MV Sewol (which was constructed in Japan in 1994) in 2012. Chonghaejin then built an exhibition room on the vessel’s stern (rear) and increased the number of guest cabins. The Sewol that ended up sinking was 239 tons heavier than its original Japanese version, drastically reducing the ship’s stability.

The Sewol was licensed to haul up to 987 tons of cargo. Yet the Special Investigation Commission on Social Disasters found that it was hauling 2,214 tons — including 185 vehicles (584 tons) — when it sank. When the vessel’s operators attempted to make it turn, this cargo shifted entirely to one side, which accelerated its sinking. CCTV and black-box footage have revealed that over half the cars the Sewol was carrying were not properly secured or tied down.

The Sewol had a full-load displacement of 9,907 tons. It’s therefore not a coincidence that the vessel took only 101 minutes to begin sinking after it had tilted over. Normally, vessels comprise several separate compartments, each self-contained. That is why a ship will not sink after it has tilted or capsized, because the air in the compartments keeps it afloat. The hull investigation panel discovered that two water-tight doors and five manholes were open on the Sewol’s E deck. Standard protocol dictates that they should have been closed. 

According to simulations run by both the hull investigation panel and MARIN, the vessel would have stayed afloat longer at a tilt of 65 degrees had the water-tight doors and manholes been closed. In short, there would have been sufficient time for a successful rescue operation.

We still don’t have the full truth. Yet three separate investigations and the vessel’s recovery have uncovered a great deal. If the vessel’s operators had considered safety instead of profiting from the vessel’s alterations; if they had properly secured the vessel’s cargo; if they had closed the water-tight doors and manholes; if the crews and captain had been properly trained to respond to emergencies — we could have saved the lives of 304 people. 

For the past 10 years, people have been asking why the responsible parties did not take at least some of the several opportunities to prevent disaster.  

By Jung Hwan-bong, staff reporter

Please direct questions or comments to [english@hani.co.kr]

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