The DEEP DRILLER is loaded as shown in the Sample Load Form #1 (Transit). Severe motion makes it necessary to ballast down to survival draft. It is decided to check stability at the intermediate draft of 32 feet. If the added ballast has an average VCG of 9.03 feet, and the sum of free surface moments is 56,244 foot-tons, what is the new GML?
• How added ballast with a known VCG changes the combined VCG of the unit • How free surface moments reduce effective metacentric height (GM and GML) • Using the definition of GML = I / ∆ − KG or equivalent form at the new draft
• Start from the known displacement and KG at the transit condition, then combine with the added ballast weight and its VCG to find the new KG before free surface corrections. • Compute the free surface correction using the given total free surface moment and the new displacement; then subtract this correction from the intact GM to get the effective GML. • Check whether you should be using transverse or longitudinal parameters for this question, and how that affects which moment of inertia or GM term you are adjusting.
• Confirm you are using the correct displacement at 32 ft draft when applying the free surface correction (FSM/∆). • Be sure to combine weights using the moment-summing method: (W₁·KG₁ + W₂·KG₂) / (W₁ + W₂). • Verify that you apply the free surface correction in the correct direction (it always reduces the effective GM/GML, never increases it).
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