Wednesday, January 19, 2011

Oasis of the Seas Damaged Stability Test

On the following Youtube video, we can see how a model of the Oasis of the Seas was being tested in a towing tank. This cruise ship would be expected to carry 6,296 guests (source: Oasis of the Seas Fast Facts). This is a huge number of passengers that has ever been carried by a man-made floating structure. To ensure that the ship is safe at sea, naval architects had to perform a number of model tests that are related to her resistance and propulsion as well as her stability particularly when one or more of her compartments are flooded with water.

In the Youtube video, we can see how a damage stability was conducted to assess how the cruise ship would react if one of her compartments was filled with sea water. The inclination of the hull would not endanger the safety of the cruise ship and her passengers on board. Although cruise ships with wider hulls have better stability performance, their damaged stability performance has to be calculated and tested to avoid catastrophic accident at sea.
Naval architects always have to prepare theoretical stability calculations to assess the metacentric height relative to the positions of the center of gravity and the center of buoyancy of the ship. The ship has to be able to restore herself to upright position when it is hit by big waves from the port or starboard side.
I believe that before she was launched, naval architects who designed the ship had fulfilled the stability requirements stipulated by SOLAS and the classification society which the ship is classed. Theoretically, the hull of a ship is divided into several compartments using transverse and longitudinal watertight bulkheads. When one of the compartments was damaged due to collision, ship crews have to close the effected compartment to prevent water from entering the other compartments. So, it is understandable to see hydraulic powered doors installed in certain rooms of Oasis of the Seas or other ships below their main decks. Usually when a hydraulic door is operated, it will close slowly and most often with an alarming sound and lamp to warn passengers or crews that it is closing. Because the hydraulic powered doors are made of steel and are driven by machines, they cannot easily be penetrated with sea water.
In very rare cases, when a compartment has been filled with water and the degree of inclination is too big thus endangering the ship, another compartment has to be flooded to balance or to make the ship returns to her upright position again. As long as the minimum freeboard, to ensure that she will not sink, can be maintained the flooding of the undamaged compartment is allowed given that the decision to fill the compartment (with full consent from the captain) has been carefully studied based on the available hydrostatic tables particularly the flooding table of the ship. by Charles Roring

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