While underway in a field move with the lower hulls awash, a semisubmersible has an allowable KG of 63.69 feet; KMT is 65.12 and KML is 64.92. The KGT is 56.13 and KGL is 55.89. What is the GML?
• Relationship between KM, KG, and GM (metacentric height)** • Difference between transverse and longitudinal metacentric heights (KMT vs KML, KGT vs KGL) • Using the correct pair of values to find GML for longitudinal stability
• Ask yourself: For GML, should you be using the transverse or longitudinal metacentric and gravity positions? • Which given values (KMT, KML, KGT, KGL, allowable KG) are actually needed to compute GML directly? • Once you pick the right KM and KG, what simple subtraction gives you GM?
• Be sure you are using longitudinal values: look carefully at the subscripts T vs L. • Confirm you are using the actual KG that matches the axis you are working in, not the allowable KG value. • Double-check your arithmetic: GM = KM − KG so GML must be KMₗ − KGₗ, with units in feet.
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