Analysis of the cause of the Ferry Sewol's rollover and sinking -

- Analysis of the cause of the Ferry Sewol's rollover and sinking -

A. Raising the question

April 16, 2024 marks the 10th anniversary of the Ferry Sewol disaster.

We pray for the souls of the "304" victims who died differently and share the sorrows of the bereaved families.

However, the bereaved families still demand an investigation into the Ferry Sewol disaster, but they do not seem to be able to approach the "core cause" of the investigation.

In the meantime, external factors such as submarine collisions raised by false experts, breakdowns of solenoid valves in Steering Gear, and factors such as stabilizer were found to be untrue after lifting the Ferry Sewol.

So what caused the Ferry Sewol to capsize and sink?

I believe that the first cause of the Ferry Sewol disaster is "the loss of Ferry Sewol's resilience."

In particular, I think there is a problem with the main data that affect resilience after the change in the hull structure due to the modification of the Ferry Sewol.

For reference, he has experience as a navigator and captain in his large-scale merchant ship, and has long lectured at the university with his book, "The Structure and Resilience of Ships."

Therefore, the main content of this posting is "loss of Ferry Sewol resilience".

Let's get to the point.

If you look at page 11 of the Ferry Sewol Special Investigation Report of the Marine Safety Tribunal,

The total tonnage of the Ferry Sewol before renovation is 6,586 tons, and after renovation, it is 6,825 tons, increasing the total tonnage (volume tonnage) of 239 tons.

In addition, the equilibrium water tonnage increases by a whopping 1,333 tons to 370 tons before renovation and 1,703 tons after renovation.

As the total tonnage of Ferry Sewol increases by 239 tons, it increases the equilibrium tonnage by 1,333 tons to lower the center of gravity of the Ferry Sewol.

In a word, the increase in the number of tons of equilibrium water in the Ferry Sewol seems to be a "sign of considerable concern for Ferry Sewol resilience" after renovation.

This results in a change in the "Center of Gravity (G)" of the Ferry Sewol.

In other words, the Ferry Sewol had a center of gravity (G) of "11.27 meters" from the keel and vertically upward before the renovation.

In other words, the KG before the renovation was 11.27 meters.

However, after the renovation of the Ferry Sewol, "Korean Register: KR," Korea's leading ship inspection agency, analyzed that the Ferry Sewol "KG" was "11.78 meters" and the center of gravity (G) of the Ferry Sewol after the renovation was "shifted 0.51 meters" vertically upward.

I question these data from "Korean Register (KR)".

The reason is as follows .

The "Ferry Sewol Hull Investigation Committee" conducted the following "calculations of the resilience of the Ferry Sewol's departure time and the time of the accident."

1) Resilience of Ferry Sewol at the time of departure
According to the calculation results, Ferry Sewol estimated that "GM was 0.74 m at the time of departure."

2) Estimating resilience at the time of an accident
According to the calculation results, Ferry Sewol said, "At the time of the accident, GM estimated 0.64m (Report P.213).

I believe that the survey results of these estimates of the GM value of the "Ferry Sewol Hull Investigation Committee" were based on basic data after the Ferry Sewol renovation of the "Korean Register (KR)."

Then, I would like to explain "GM".

"G" is the "Center of Gravity (G)" of the ship, which refers to the point where the entire weight of the ship can be considered at any point.
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In addition, the "Metercenter: M", the center of inclination of the hull, is the intersection between the ship's 浮力 line and the upright ship's center line when the ship is inclined at a small angle when it is upright, that is, the 垂 line erected by the 浮 line and the ship's center line meet when the ship is inclined.

Therefore, "GM" refers to the vertical distance between the "G" point and the "M" point, and the change in the G and M points has a very important meaning for the ship's resilience.

Let's take an example.

1. When the "G" of the ship is located below the "M" (G below M).
In this case, when the external force acting on the ship disappears, it immediately returns to its original position (standing state), so it can be said that there is a restoring moment, and the ship is in a stable equilibrium state.

In addition, since the "GM" of a ship in this state becomes "GM=KM-GM>0, it is considered to have positive (+) positive stability, and the larger the "GM value", the greater the resilience of the ship.

2. If the ship's G is raised and the G and 傾 M match (G coinside with M),

In this case, since there is no "GZ (Righting Arm or Righting Lever)", even if there is no external force, there is no righting moment, so the ship floats on the surface with a slope.

This state of the ship can be said to be in a "neutral equilibrium state."

In addition, the "GM (Gravity to Metercenter)" of ships in this state appears as GM=KM (Kel to Metercenter)-KG (Kel to Gravity)=0."

In fact, if a ship is in this state, it is highly likely to overturn if the loaded cargo is moved or the ship's horizontal and wave cycles are synchronized.

Therefore, the cause of the Ferry Sewol disaster was the "G=M" of Ferry Sewol at the time of the disaster, that is, the "GM value is Zero" of Ferry Sewol, and proving it is also proved in the following "time table."

However, this is too different from the "GM 0.64m," the restoration estimate at the time of the Ferry Sewol accident, calculated by the "Ferry Sewol Hull Investigation Committee."

If the GM value of the Ferry Sewol at the time of the Ferry Sewol disaster was "0.64m", it can be said that the Ferry Sewol occurred like a rooster.

It's absolutely ridiculous data.

Therefore, I think that the start of the fact-finding of the Ferry Sewol disaster should begin here.

3. When the ship's center of gravity "G" is raised above the diameter "M" (Gove M),

In short, this time zone is the time zone for the overthrow of the Ferry Sewol.

In other words, the Ferry Sewol set sail from Incheon, and until it takes a detour in front of Byeongpungdo Island,

It seems that G is below M, so there was some resilience (G bellow M),
Around 08:46 on April 16, 2014, the starting point of the change, it can be said that the resilience of the Ferry Sewol was "Zero".

If G=M, the ship is in a state of no resilience and is floating on the surface with a slope.

In other words, the ship cannot return to its original position because the "Righting Moment" is in the "Zero" state.

If this G=M condition continues, a large-angle transverse slope is created due to the mass movement of unpacked cargo,

Due to the watertight doors of the C and D decks of the unsealed Ferry Sewol, enormous seawater is rapidly invaded into the ship, creating a diagonal horizontal slope in the inclined direction and overturning the ship.

This state is "Gabove M" where G came up above M.

B. Time table at the time of the Ferry Sewol disaster

1. 4April 16, 2014 at 08:46 PM

As Ferry Sewol passed through Byeongpungdo Island in Jindo-gun at around 08:46 on April 16, 2014, it made two stools, 135 to 140 degrees, and 140 to 145 degrees, 5 degrees, each at around 08:49.

But the Ferry Sewol, despite the burning of five degrees, has not settled at 145 degrees and continues to detour, almost turning around in a big circle, and then the engine goes off,

As the speed decreased, an outward slope (a phenomenon in which the ship tilts in the opposite direction of the winding) occurred, and the Ferry Sewol was unable to stand up, inclined about 15 degrees to the port.

In other words, this state of the Ferry Sewol, that is, on April 16, 2014, at 08:46, is the state of "G=M", and the GM value is "Zero".

If there was a resilience of the Ferry Sewol at the time, the Ferry Sewol becomes upright while standing straight after leading directly from the initial inner slope to the outer slope.

However, the Ferry Sewol at the time was not resilient, so after being inclined, lying down, it could not return to its original position (standing state).

2. April 16, 2014, 9:17 PM

Ferry Sewol had a slope of approximately 50 degrees at 9:17 p.m. on April 16.

In other words, from this time point, the Ferry Sewol is starting to roll over the "G" and the Ferry Sewol is starting to roll over the "M".

Therefore, from 08:46 on April 16, 2014 to 9:17 on April 16, "31 minutes" was a golden time to rescue all the young students, passengers, and crew in Ferry Sewol, and it was enough time, but the rescue failed.

3. April 16, 2014, 10:25 PM

Ferry Sewol had a slope of approximately 108 degrees to the port at around 10:25 on April 16.

4. April 16, 2014, 10:31 PM

On April 16, around 10:31, Ferry Sewol was overturned with a slope of 180 degrees to the port.

5. April 16, 2014, 12:57 PM

The Ferry Sewol completely sank on 16 April at 12:57.

C. What was the "GM value" at the time of departure of the Ferry Sewol?

The Ferry Sewol hull investigation committee" calculated the "resilience calculation at the time of departure of the Ferry Sewol" as follows.

1. Resilience of Ferry Sewol at the time of departure
According to the calculation results, Ferry Sewol estimated that "GM was 0.74 m at the time of departure."

2. Resilience at the time of the Ferry Sewol accident
According to the calculation results, Ferry Sewol said, "GM estimated 0.64m at the time of the accident."

3. Conditions of departure at the time of departure from Ferry Sewol

Let's look at the conditions of Ferry Sewol's departure at 21:05 on April 15, 2014.

1) Cargo volume: 2,143 tons (press release)
2) Number of people on board: 39.87 tons
Passengers: 476 passengers (443 passengers, 33 crew members), 33 crew members were inserted into the Unknown Constant (unknown weight), and the weight of 443 passengers was calculated to be 39.87 tons (comprehensive report)
3) Fuel: 128.4 tons (special report)
4) Equilibrium water: 761.3 tons (special report)
5) Freshwater: 192 tons (special report)
6) Food and beverage: 0.7 tons (comprehensive report)
7) Unknown weight: 166.2 tons (comprehensive report), etc.

Then, the Ferry Sewol left Incheon Port at 21:05 on the 15th of 2014,