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| The Navy and Coast Guard step up rescue-and-search operations in the location of the Sewol ferry sinking near Jindo, South Jeolla Province, Tuesday, as the current is slow. / Yonhap |
By Nam Hyun-woo
Questions about the cause of the ferry Sewol's sinking have been raised because its location tracking records show that the vessel did not make a sharp turn before beginning to list.
The Ministry of Oceans and Fisheries has so far suspected that the vessel lost stability and sank because the cargo on the ferry shifted during a sharp turn. But the ship's automatic identification system (AIS) record showed that it made a relatively gradual turn, creating a "J-shaped" wake.
In the record, released late Monday, the ship was on its initial course until 8:48 a.m., Wednesday.
It started veer right by about 45 degrees for 19 seconds, from 8:49 a.m. The ministry speculates that it lost stability during that period and started to list leftward.
The vessel continued a rightward turn and was some 115 degrees off its initial route at 8: 52 a.m.
Ministry officials assume that the ship's engine was apparently turned off during that three-minute period.
At that point, the ship drifted to the north and capsized in waters some 20 kilometers north of Byeongpoong Island.
Before this analysis, it was believed the vessel made a sharp 115-degree turn to evade potential obstructions, because the AIS record of the ship's location for 3:36 seconds, from 8:48:27 a.m. to 8:52:13 a.m., was lost.
Authorities managed to restore most of the missing information, but the records of 36 seconds ― from 8:48 a.m. to 8:49 a.m. ― were still unavailable. They estimate that the ship's electricity went dead at that point.
As the record shows that the vessel listed while making a gradual 45-degree turn, new speculation is being raised about why the ship was unable to handle the turn.
Adding extra cabins to the ship may have caused the ship to easily loose stability. After purchasing the ship from a Japanese company two years ago, Chonghaejin Marine, the ferry's operator, renovated it to accommodate almost 150 additional passengers and 240 tons of additional cargo.
According to Prof. Kim Gwang-soo of the Mokpo National Maritime University, extending a ship's height affects its metacentric height, which is critical to a ship's stability.
Overloading also may have contributed to the accident. The Korean Register of Shipping directed the ship to load at least 2,030 tons of ballast water in order to secure stability. Thus the ship, which carried 180 vehicles and 1,157 tons of cargo, may have lacked sufficient ballast water, experts said.
Another suspicion is that mechanical defects may have contributed to the accident.
During the investigation by a joint team of prosecutors and police, a third mate, who was navigating the ship when the accident occurred, said she ordered the helmsman to turn 5 degrees to the right. The helmsman also said he tried to comply with the order but the wheel "turned more" than he steered.
Prof. Yoon Jong-hee of Korea Maritime and Oceans University said, "The steering wheel operates by oil pressure, so it cannot be over-steered more than it is actually turned."
"If the helmsman's claim is true, there could be mechanical defects in the wheel."
If there was a 36-second blackout, the ship's wheel may have been affected. There is also the possibility that the wheel could have been defective to start with.
A ministry official said, "Further investigations are needed to confirm whether there was a blackout, and if it caused any malfunctions." He added that after the ship is salvaged, investigators will be able to determine whether the ferry was overloaded or there was a lack of sufficient ballast water.
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