The DEEP DRILLER is drilling at 60 feet draft at a corrected KG of 54.0 feet. Ballast added or discharged to remain at a constant draft is at a VCG of 10 feet. How much non-liquid load would have to be removed from an average height of 130 feet above the keel to meet the maximum allowable KG at a draft of 60 feet for winds greater than 70 knots?
• KG vs. VCG – how removing weight at a certain height changes the overall KG of the unit • Mass moments – using weight × height (w × z) to calculate the effect of adding/removing weights on KG • Stability criteria for 60 ft draft and >70 knots wind – the maximum allowable KG for this draft and wind condition (from the stability data booklet)
• First, think about how to express the current total displacement and vertical moment of the unit using the given KG of 54.0 ft. • Ask yourself: how does removing weight at 130 ft affect the total vertical moment and therefore the new KG? Set up an equation for the new KG after removing an unknown weight. • Consider the ballast at VCG 10 ft: if draft must remain 60 ft, what must happen to the ballast when you remove non-liquid load so that displacement (and draft) stay constant?
• Be sure you are using KG = (Total vertical moment) / (Total displacement) correctly, with consistent units (long tons and feet). • Confirm that displacement at 60 ft draft before and after changes is the same, so any non-liquid load removed must be balanced by ballast added or discharged. • Verify that the final computed KG matches the maximum allowable KG at 60 ft draft for winds >70 knots before choosing the closest answer.
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