Your vessel's drafts are: FWD 21'-08", AFT 24'-02". The LCG of the forepeak is 200 feet forward of amidships. How many tons of ballast must be pumped into the forepeak in order to have a drag of 15 inches? (Use the selected stability curves in Section 1, the blue pages, of the Stability Data Reference Book)
• Using trim and stability curves from the Stability Data Reference Book (blue pages) • Relationship between change in trim, TPI (tons per inch immersion), and LCF/LCG • Effect of adding weight forward of amidships on draft forward and aft
• First, figure out the current trim (drag) in inches from the given drafts. Then, determine the desired trim and how much change in trim is required. • Think about how to use the trim curves or tables: what information do you need from the book to link a change in trim (in inches) to a required trimming moment (ton-feet)? • Once you know the trimming moment needed, ask: how do you convert that moment into tons of ballast in the forepeak given its LCG relative to amidships?
• Be sure you convert feet and inches to decimal feet (or inches) consistently before using the curves. • Verify the correct use of distance of LCG of added weight from LCF/amidships when calculating trimming moment. • Check that the sign of the trim change is correct: adding weight forward should change which draft (forward or aft) more?
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