Your vessel's drafts are: FWD 18'-09", AFT 20'-05"; and the KG is 23.8 feet. Use the selected stability curves in the blue pages of the Stability Data Reference Book to determine the righting arm at 30° inclination.
• Use of stability curves in the blue pages of the Stability Data Reference Book • Effect of actual KG vs. curve KG (applying the freeboard correction / KG correction to GZ) • Interpreting GZ (righting arm) at a specific angle of heel (30°)
• First, identify which standard stability curve in the blue pages matches the vessel’s displacement and draft condition closest to FWD 18'-09" and AFT 20'-05". What page/curve should you be on? • On that curve, find the GZ value at 30°. Then ask: is this value for a standard KG, or must you apply a correction because your actual KG is 23.8 feet? • Think about how an increase in KG affects the righting arm: does it make GZ larger or smaller? How does that influence which numerical choice is reasonable?
• Verify the correct displacement / draft curve has been selected before reading any GZ values. • Check whether the GZ curve you’re using is based on a reference KG (KGo) that is different from the actual KG given (23.8 ft) and whether a KG correction table or formula must be applied. • Confirm you are reading GZ at exactly 30° (not nearby angles) and converting correctly (e.g., reading in feet, not meters, and interpolating if necessary).
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