Your vessel's drafts are: FWD 19'-03", AFT 21'-03". 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 18 inches? (Use the reference material in Section 1, the blue pages, of the Stability Data Reference Book)
• Trim and draft change: Relationship between weight added at a known longitudinal position and change in trim/drag • Using the vessel’s moment to change trim 1 inch (MCT 1") from the Stability Data Reference Book • How LCG of weight added relative to the vessel’s LCF (Longitudinal Center of Flotation) affects trim
• First, calculate the current drag and compare it to the desired drag of 18 inches. Are you increasing or decreasing trim by the stern? • Identify the distance between the LCF (from the reference material) and the LCG of the forepeak tank. How does this distance affect the trimming moment created by ballast added forward? • Use the standard trim formula: relate the trimming moment (weight × distance) to MCT 1" to find how many tons are needed for the required change in trim.
• From the blue pages, get the correct MCT 1" and LCF position for the ship’s displacement closest to this condition • Be sure you use feet for distances and inches for trim consistently in the trim formula, converting where necessary • Confirm whether the requested 18 inches is total drag after ballasting or the change in drag, and adjust your trim-change calculation accordingly
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