The SS AMERICAN MARINER arrived in port with drafts of: FWD 28'-08", AFT 29'-05". Cargo was loaded and discharged as indicated in table ST-0013 below. Use sheet 2 in the white pages of the Stability Data Reference Book to determine the final drafts.
Discharge 120 tons---145 feet fwd of amidships Load 160 tons---87 feet fwd of amidships Discharge 85 tons---50 feet fwd of amidships Discharge 100 tons---30 feet aft of amidships
• Use TPI/MT1 from sheet 2 of the Stability Data Reference Book to convert change in weight and trimming moment into changes in draft. • Separate the problem into change of mean draft (total weight on/off) and change of trim (moments about amidships). • Remember sign convention: weights forward of amidships create a trimming moment by the head; weights aft of amidships create a trimming moment by the stern.
• First, what is the net change in displacement (tons loaded minus tons discharged), and how will that affect the mean draft using TPI/MT1? • Next, what is the algebraic sum of all trimming moments (tons × distance from amidships), and how do you convert that total moment into change in trim (difference between forward and aft drafts) using the trim constants on sheet 2? • Once you know the change in mean draft and the change in trim, how do you apply half the trim to the forward and aft drafts to get the final drafts?
• Be sure your signs are consistent: assign a positive or negative direction for forward moments and stick with it for all four weight changes. • Verify that the sum of individual moments (each weight × its lever from amidships) equals the total trimming moment before using the trim formula. • After you compute the new drafts, check that forward + aft drafts ≈ 2 × mean draft; if not, recheck your arithmetic.
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