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46 Y.A. SOYADI, Y.A. SOYADI, Y.A. SOYADI ve Y.A. SOYADI

Point of Vanishing Stability will result in rotation until equilibrium is maintained. With this
attitude ship can be more stable when upright.

In order to achieve a self-righting design, the vessel must fill three fundamental requirements
[6]:

 Possess a curve of righting levers for which there is no Point of Vanishing Stability
which possible with positive GZ curve throughout the full 360 degrees’ rotation.

 Become unstable when inverted to initiate the righting process until vessel become
upright position.

 Remain buoyant and watertight.

3. Self-Righting Methods
To provide the criteria mentioned above, self-righting craft usually own a non-flooding hull and
sufficient buoyancy suitably placed to ensure that the vessel is unstable when inverted. In case
of large vessels size of superstructure generally produce adequate buoyancy, with all hull and
opening being non-flooding or self-closed to keep watertight integrity. Such vessels have
inherently self-righting the capability is in the design. For small boats, lacks of space for large
superstructure usually prevent inherited self-righting ability. In order to achieve self-righting use
of inflatable bag can be used. Inflatable bag can be either triggered automatically or manually
by crew when vessel is capsized. Third method is the moveable weight method called
commonly water ballast. Moving weight causes an instability when ship is capsized resulting a
positive righting moment.

Neither inflatable bag nor moving weight prevents capsizing. This methods used after passing
the point of vanishing stability to ensure instability until ship is come to its upright position.
After that normal form and stability criteria comes into play.
One essential of any self-righting vessel is the relationship between weight and buoyancy to
obtain required stability curve. One achieved this curve in rolling process; nothing should
disturb it and impaired the recovery process. Meaning that, crew, passengers, and equipment
should not move and change the ship’s center of gravity. Thus, securing the crew and
passengers is also an important criterion for self-righting vessel design.

3.1 Inherent Self-Righting
Boats utilizing this method have their self-righting ability where it is always available and will
return upright from any angle of heel regardless of crew’s additional action.

GiDB|DERGi Sayı 6, 2016