Damage Stability Analysis
Punch a hole in the hull, and the vessel still floats. It isn’t luck. That resilience relies on damage stability analysis. This is the careful of science of considering damage scenarios and planning to ensure the vessel remains floating and upright after each possible damage. This contingency planning offers great reassurance after you heave the bang of collision against the hull. This can take many forms.
At the concept design stage, we generally only consider a simple floodable length analysis. The floodable lengths merely check that the vessel has sufficient reserve buoyancy. Naval architects use this analysis to determine maximum spacing between transverse bulkheads.
Deterministic Damage Stability
As the design progresses, a deterministic damage stability analysis checks that the vessel remains stable and upright in all damage conditions. Commonly, we just call this a damage stability analysis. The only way to be sure about safety in a damaged condition is to check every scenario of damaged tanks and compartments. A typical damage stability analysis consists of several steps.
- Regulatory research – determine the exact set of stability criteria
- Hydrostatic modeling, with additional features
- Internal compartmentation
- Cross flooding links
- Margin line definition
- Bulkhead locations (for floodable length analysis)
- Damage conditions
- Maximum VCG analysis
- Develop loading conditions
- Check loading conditions
- Document results in analysis report
Damage stability analysis requires extensive repetition. We need to develop a maximum VCG curve for each damage condition. Thankfully, Maxsurf Stability makes this an automated process. We setup the combinations and let the computer run through all possible combinations.
DMS also searches for ways to develop added value for our clients. Our reports identify the critical damage conditions. If possible, we suggest changes that may improve your damage stability performance. This
Probabilistic Damage Stability
For many vessels, regulations require a probabilistic damage stability analysis. Imagine this as a deterministic damage stability analysis, on steroids.
A deterministic analysis starts by specifying an extent of damage. We draw a box of the specified dimensions (determined by regulations). This extent of damage is the size of the fictional object that punctured the hull. Any tanks or compartments within that box get flooded. The damage cases form from checking all possible combinations that simultaneously lie inside the extent of the box.
Probabilistic damage stability goes further. It requires many, many more combinations. In a probabilistic analysis, there is no limiting box. This approach acknowledges that any combination of damage scenarios are possible. We must consider all combinations of potential damage. From one tank, to raking across four compartments along the side of the hull. (Naturally, the vessel fails some extreme damage conditions.) The regulations then prescribe rules to determine the probability of each damage scenario. By combining the damage survival with the probability, we get a score for each damage scenario. Add all the scores together to determine how well your vessel did. The regulations also specify a minimum limit for your total score. Exceed the minimum limit, and the vessel passes probabilistic damage stability.
This method offers designers much more flexibility for layout of the vessel. It better reflects the real world. Do you really expect to find an iceberg exactly 10 m long and 3 m wide? The probabilistic approach allows for variations. But that flexibility requires far more iteration. And much more complicated mathematics to reflect the reality of each potential combination.
Thankfully, Maxsurf Stability includes automations to rapidly progress through all possible combinations. Computers perform very well at repetitive tasks. With the aid of Maxsurf Stability, DMS can offer probabilistic damage stability analysis at reasonable prices.
FREE Loading Condition Spreadsheet
DMS also cares about delivering practical utility to the vessel crew. Ultimately, stability analysis should be a tool for the vessel master to ensure safe operation. The best tools are easy to use and convenient. Along with the stability analysis, we also provide a free loading condition spreadsheet. This incorporates your custom tank properties and MaxVCG curves. It allows you to easily develop custom loading conditions for yourself.
Plan your own burn-ballast sequence for each voyage. Safely check transfers between tanks. Other firms may charge you tens of thousands for a fancy program that achieves the same functionality. But at DMS, we think the knowledge is more important than the appearance. That is why we automatically include the loading condition spreadsheet with each stability update that includes a trim and stability booklet. Want to learn more about your free loading condition spreadsheet? We’re happy to talk.
The fine print:
- Loading condition spreadsheet is NOT a substitute for a class approved loading computer. It is only a convenient tool for the vessel master.
- Stability update requires a full trim and stability booklet to provide a free loading condition spreadsheet. Stability letters and stability assessments do not receive a free loading condition spreadsheet.
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