Passenger Ship Stability

An owner repowered and refit their vessel for passenger service under Subchapter T.  After completing most of the work, the shipyard hired DMS to perform a stability assessment and stability test.

 

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Stability Assessment

Initially, we hoped that a full stability test would not be required.  So DMS adopted a two-stage assessment plan:

  1. Stability assessment only.  Determine if we need a fully stability test or just a light ship survey.
  2. Incorporate the results of the stability test and perform the full stability assessment for USCG approval.

DMS completed the stability assessment, including:

  1. Develop stability model
  2. Regulatory research
  3. Intact stability analysis
  4. Damage stabilty analysis
  5. Develop loadcases
  6. Maximum KG analysis

The results ultimately revealed that a stability test was required.

 

Stability Test

DMS determined that a full stability test was necessary.  DMS conducted the full stability test.

  1. Prepare stability test procedure.
    1. Obtain USCG approval of procedure.
  2. Conduct stability test.
    1. Preliminary results were presented on the day of the test.
  3. Prepare stability test report.

Most stability tests require flexibility, adapting to changing circumstances.  When we arrived on site, DMS discovered that the ship center of gravity did not match the estimated position, which completely changed the test plan.

Within one day, DMS adjusted the test plan, calculating new positions for the test weights, removing excess deadweight, and working around the weather.  In the end, we obtained 100% reliable test results.

Stability Corrections

The stability test discovered that the vessel could not pass current USCG stability requirements.  At this point, DMS provided support to determine potential solutions.  We understand the challenge of correcting insufficient stability.  Handled incorrectly, it can be frustrating and expensive.  Rather than dictating a path forward, DMS sat down with all parties involved and presented several options:

  1. Reduce passenger capacity.
  2. Add fixed ballast.
  3. Add a bar keel.
  4. Add sponsons.
  5. Remove vessel structure on top to reduce weight.
  6. Various combinations of the above options.

Time was essential, so DMS picked a strategy to keep the project moving forward.  We didn’t waste time with long winded reports.  Instead, once DMS had results, we presented everything in a phone conference, allowing the owner to make their own decision on how to proceed.  DMS offered the ability to take immediate action.  

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