Page:Self-righting boat design.pdf/6

 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: 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.
 * 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

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. 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.
 * 3.1 Inherent Self-Righting