Audio Overview Ch 9 Part 2 Change_of_Trim_and_Drafts

STABILITY AND TRIM FOR THE SHIP'S OFFICER, 4th Edition, by William E. George Change of Trim and Drafts Source Material: Pages 190–192, 193–196 This Audio Overview focuses on the precise distribution of trimming forces and the correction of physical draft readings to the mathematical "Physical Truth" of the perpendiculars. I. Mechanics of Trim Change: Shifting vs. Loading (Pages190–191) Shifted Weights: When weight is pumped or moved longitudinally, the mean draft remains constant. The Change of Trim is calculated by dividing the trimming moment (Weight × Distance moved) by the MT1 (or MTC). Loaded or Discharged Weights: Calculated using the "Assumed Condition" two-step logic. Step 1: Assume the weight is loaded at the tipping center (LCF). Calculate parallel sinkage (Weight ÷ TPI or TPC). Step 2: Calculate the trimming moment created by shifting that weight from the LCF to its actual longitudinal position. Divide by MT1 (or MTC) to find the change of trim. II. Calculating Exact Distribution of Trim Change (Page 192) The Inaccuracy of Amidships: Because the LCF (tipping center) rarely coincides with amidships, equal distribution of trim is not strictly correct. Proportional Method: To find the exact change at each end, use the distance from the LCF to the draft marks compared to the total length between the marks. Change at Forward Marks = Change of Trim × (Distance from LCF to Forward Mark ÷ Length between marks). Change at After Marks = Change of Trim × (Distance from LCF to After Mark ÷ Length between marks). III. Trimming Point: Change of Draft at One End Only (Pages 193–195) The Physical Rule: To change the draft at only one end, the parallel sinkage must exactly equal one-half of the change of trim. The Special Formula (d): d=2×MT1/TPI (or 2×MTC/TPC). Operational Behavior: Loading weight at distance d Forward of the LCF results in an increased Forward draft while the Aft draft remains constant. Loading weight at distance d Aft of the LCF results in an increased Aft draft while the Forward draft remains constant. IV. Effect of Trim on Draft Readings (Pages 195–196) The Mark/Perpendicular Gap: Draft marks are rarely located exactly at the Forward and After Perpendiculars. When a ship is trimmed, the drafts read at the marks must be corrected to the perpendiculars. Correction Method: Find the trim in inches per foot of length (Total Trim ÷ Length between marks). Multiply this value by the distance between the draft marks and the corresponding perpendicular. Verification: All trim calculations predict drafts at the perpendiculars. Officers must investigate the mark-to-perpendicular correction for their specific vessel to ensure the "Physical Truth" of their readings. Produced by William E. George and Powered by Google's NotebookLM. Become a supporter of this podcast: https://www.spreaker.com/podcast/stability-trim-for-the-ship-s-officer--4180737/support.