The COASTAL DRILLER is loaded as shown in the Sample Load Form #1 (Rig Move). If the entire contents of bulk tanks #2 and #3 are back-loaded to an offshore supply vessel, what longitudinal moment would have to be created to level the unit in trim at the new draft?
• Longitudinal center of gravity (LCG) and how it shifts when weight is removed or added • Relationship between trimming moment and change of trim: Moment = (Change in Trim × TPI × L/Δ) or the equivalent formula given in your exam stability booklet • Using the sample load form data to find the initial and final LCGs and the moment needed to bring them to the same point
• First, determine how removing the contents of bulk tanks #2 and #3 changes the total displacement and the combined LCG of the rig. Where were these tanks located longitudinally? • From the sample load form, figure out the new trim after the cargo is removed. Then, what trimming moment (about the center of flotation) would be needed to bring the trims at forward and aft drafts back to equal? • Use the trimming moment per unit trim (MTC or equivalent value in the problem materials). Given the required change in trim (in feet), what total moment does that correspond to?
• Make sure you are using the correct longitudinal arms for tanks #2 and #3 from the sample load form, and that you convert any inches of trim to feet before calculating moments • Verify that the displacement and hydrostatic values (like MTC or Moment per Inch/Foot of Trim) correspond to the new draft, not the original draft • After you compute the required longitudinal moment, check whether its magnitude makes sense: removing weight from forward or aft should change trim in a direction consistent with the sign of your moment, and the numerical result should be in the same order of magnitude as the given answer choices
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