A semisubmersible with a displacement of 20,000 tons and KG of 52 feet discharges 300 long tons of barite from P-tanks located 120 feet above the keel. Ballast added to maintain draft has a VCG of 20 feet. What is the change in KG?
• Movement of the center of gravity (KG) when weight is removed high and added low • Using the moment = weight × vertical distance idea to track changes in KG • How to properly handle long tons vs displacement tons in stability calculations
• What happens to the vessel’s KG when you remove weight from a very high point and then add weight at a much lower point? Think about whether KG goes up or down overall. • Can you compute the moment lost when removing the barite and the moment gained when adding ballast, then combine these to find the net change in total moment and new KG? • Are you correctly relating the change in total vertical moment to the change in KG using the total displacement as the reference?
• Be sure you use displacement (20,000 tons) as the basis when converting total moments into a change in KG. • Keep the vertical distances from the keel straight: 120 ft for the tank and 20 ft for the ballast. • Check the signs of the moments: removing a high weight versus adding a low weight should have opposite effects on KG.
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