Abstract
The chapter describes main principles of intact and damage stability, including the latest probabilistic (SOLAS 2020) and older deterministic damage stability rules (SOLAS 90). Simple calculation examples are shown for calculating GM and free surface effect. Meaning of the “load line mark” seen on the side of every ship is explained and a useful quick means to estimate the stability of a cruise ship project is presented. Principle of an inclining test, or “weighing a ship”, is explained, along with description of how the weight of cruise ships continuously increases as the ship ages.
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Notes
- 1.
New inclining test is also needed, if the ship is modified and the calculated weight increase exceeds the limits (2% increase in lightweight, 1% change in LCG or 1% change in VCG). If the calculated weight increase exceeds only half of these limits, updating stability calculations with the new weight is needed, but new inclining test is not required.
- 2.
Second Generation Intact Stability Code (SGISC) will replace the 2008 IS Code. This new code will include new criteria for parametric rolling, broaching, excessive acceleration, and such. Weather Criterion is included, but it is now called “dead ship condition”. SGISC has a multi-level approach: criteria have different level of checks: if vessel does not pass the first easy check, a more detailed analysis is needed, and so on.
- 3.
Factor of subdivision was calculated as per SOLAS formula, and it depended on ship’s length, number of passengers, different volumes, etc.
- 4.
Withstanding a damage means that after suffering a flooding damage the ship still has adequate level of GM to meet the required stability criteria in damaged condition. The heeling angle after the flooding must also be within certain limits. The deterministic rules also required that so called “margin line”—approximately the same as bulkhead deck level at ship’s sides—would not be immersed after the damage.
- 5.
The “R” in SOLAS 2009 was also affected by the lifeboat capacity and ship’s subdivision length. Here length of 280 m and lifeboats for 75% of persons onboard is applied.
- 6.
Probability of survival, or “s”, depends on stability characteristics after the damage: the maximum value of GZ, the available GZ range and the heeling angle. If the final heeling angle after damage is 15° or more, the s = 0. The idea is to simulate how likely the ship will remain afloat after the damage.
- 7.
The regulation can be criticized, because the applied statistics only include collision damages, which are quite rare for passenger ships. For example, long grounding damages, possibly damaging large areas of ship’s bottom, are not considered.
- 8.
For minor damages, see the info box “Does ticket price reflect safety of the ship?”.
- 9.
The loading computer usually automatically reads the tank contents, but number of passengers and crew, and weight of stores need to be input manually.
- 10.
Draft marks show the draft from below keel when the location of load line mark is based on molded draft. If the maximum draft of the ship is 8.50 m (molded draft), the top of the line going through the load line mark circle is at waterline. The draft marks, however, show 8.52 m (molded draft of 8.50 m plus the thickness of 20 mm bottom plate).
- 11.
The letters show who has issued the load line certification for the vessel. For example, earlier Finnish vessels had letters “SL”, but today, when class societies have been authorized to issue the load line certificate on flag’s behalf, classification society letters are used instead.
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Aarnio, M. (2023). Stability. In: Cruise Ship Handbook. Springer Series on Naval Architecture, Marine Engineering, Shipbuilding and Ship**, vol 14. Springer, Cham. https://doi.org/10.1007/978-3-031-11629-2_4
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DOI: https://doi.org/10.1007/978-3-031-11629-2_4
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