The large hole, about 2 meters in diameter, in the bow hull of the sunken ferry Sewol, shown in the photo (page 4, Apr. 18, The Korea Times) is called a bow thruster. It's not a rescue hole, and it does not provide access to inside the bulkhead. The Sewol had to be equipped with a stern (rear) thruster too. A bow thruster or stern thruster is a transversal propulsion device built to make a ship more maneuverable. The bow thruster makes docking easier, since it allows the captain to turn the vessel to the port (left) or starboard (right) side, without using the main propulsion mechanism which requires some forward motion for turning. The side thrusters eliminate the need for tug boats in the harbor. The submerged thrusters, however, cannot be used during normal navigation as they are designed for use when the speed of the ship is less than 5 knots.
As the Korea Times photo shows, the ship was designed with a wave-piercing bow, an example of cutting-edge naval architecture. It is designed to cut through waves, increasing the ship's performance by reducing pitch, or longitudinal sway, resistance. The Titanic had a straight stem bow.
In a related, yet far more important point of physics related to the capsizing of the Sewol, is the loss of stability. That is the center of gravity (CG) and center of buoyancy of a vessel, and how they interact. The Leaning Tower of Pisa does not topple over because its CG does not extend beyond its base. The double-decker buses in London won't topple when their chassis are tilted up to 30 degrees with the top decks fully loaded because so much of the weight of the vehicle is in the lower part, and the CG does not extend beyond its support base. It's as simple as that.
Poor loading of cargo and added rooms on the top of the stern deck, all for money, raised the CG high above the water line at the expense of stable rolling buoyancy and equilibrium, which made the ferry ready to surrender to Earth's gravity even before the ship left Incheon dock.
As the Korea Times photo shows, the ship was designed with a wave-piercing bow, an example of cutting-edge naval architecture. It is designed to cut through waves, increasing the ship's performance by reducing pitch, or longitudinal sway, resistance. The Titanic had a straight stem bow.
In a related, yet far more important point of physics related to the capsizing of the Sewol, is the loss of stability. That is the center of gravity (CG) and center of buoyancy of a vessel, and how they interact. The Leaning Tower of Pisa does not topple over because its CG does not extend beyond its base. The double-decker buses in London won't topple when their chassis are tilted up to 30 degrees with the top decks fully loaded because so much of the weight of the vehicle is in the lower part, and the CG does not extend beyond its support base. It's as simple as that.
Poor loading of cargo and added rooms on the top of the stern deck, all for money, raised the CG high above the water line at the expense of stable rolling buoyancy and equilibrium, which made the ferry ready to surrender to Earth's gravity even before the ship left Incheon dock.
Nam Sang-so
Retired architect in Seoul
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