Review and Update of U.S. Coast Guard Vessel Stability Regulations and Guidance (2019) / Chapter Skim
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Pages 145-156
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From page 145... ...
A weight-tracking program for cargo ships, or any ship, tracks the inevitable lightship weight changes that will occur over the ship's lifespan from the last inclining test or deadweight survey. The weight categories to be tracked would need to include both those that are well defined as well as weight changes that often go unnoticed because they are considered individually to have no significant impact on a cargo ship's stability.
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From page 146... ...
146 USCG VESSEL STABILITY REGULATIONS AND GUIDANCE Failure to meet both of these interrelated requirements for any ship weight-tracking program could pose more of a danger than having no weight-tracking program. For example, if the cargo ship's weight-tracking program is very cumbersome to use, it will not be maintained to a sufficient level of accuracy to reflect the actual changes in the cargo ship's lightship.
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From page 147... ...
APPENDIX E 147 personnel may have no stability education at all. Thus, persons with little or no stability training are unlikely to effectively use any weight-tracking program that requires advanced knowledge of ship stability or how changes to ship lightship affect its stability.
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From page 148... ...
148 USCG VESSEL STABILITY REGULATIONS AND GUIDANCE Accuracy in Tracking Weight Changes The second key requirement in any cargo ship weight-tracking program is its accuracy in tracking the weight changes that occur in a cargo ship's lightship condition over its lifetime and in determining when the cargo ship's stability should be reviewed. These weight changes to a cargo ship's lightship condition occur in many different forms and magnitudes, and can range from very small, such as changing the chairs in the ship's mess, to large, such as adding a new adjustable car deck in a ro-ro vessel.
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From page 149... ...
APPENDIX E 149 ship's crew to treat the weight-tracking program less seriously and ignore it. Conversely, setting too high a threshold value can have the obvious problem of missing weight changes that may have a cumulatively significant negative impact on the vessel's stability compliance.
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From page 150... ...
150 USCG VESSEL STABILITY REGULATIONS AND GUIDANCE 6. Optional: The person(s)
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From page 151... ...
APPENDIX E 151 occurs. These forms would then be forwarded to the central operations office where the information would be entered into some type of computerbased program.
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From page 152... ...
152 USCG VESSEL STABILITY REGULATIONS AND GUIDANCE determine if the vessel's stability needs to be reevaluated and by what means that should be done: revised calculations, deadweight survey, or inclining. For example, if the net change in a passenger vessel's lightship weight is less than 2%, only a mathematical reevaluation of the vessel's stability is required.
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From page 153... ...
APPENDIX E 153 for an inclining, if the gross magnitude of the weights to add, remove, or relocate is less than 2% of the final lightship weight, the inclining is acceptable as done. However, if the gross magnitude of the weights to add, remove, or relocate is between 2% and 10% of the final lightship weight, a confirmatory deadweight survey is required, and if in excess of 10%, another inclining is required.
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From page 154... ...
154 USCG VESSEL STABILITY REGULATIONS AND GUIDANCE for when this could be a concern. One possible threshold could be when an increase in lightship VCG occurs, causing a reduction in attained metacentric height in any design load case so that the margin on the required value is below a minimum margin.
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From page 155... ...
APPENDIX E 155 changes every year means a total of 50 weight changes will occur in the 5-year period. Assuming the sample ship previously mentioned were a passenger ship, its average weight change would be 460 tons divided by 50, which equals 9.2 tons per weight change.
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