The DEEP DRILLER, at 60.0 feet draft in sea water, has VM = 974,441 foot-long tons, and FSMT = 18,732 foot-long tons. What is the metacentric height corrected for transverse free surface effects?
• Relationship between metacentric value (VM) and GM (metacentric height) • How free surface moment (FSMT) reduces the effective GM • The need to use the vessel’s displacement in long tons to convert from foot-long tons to feet
• Think about what physical quantity VM represents and how its units (foot-long tons) relate to GM, which is in feet. • How do you combine VM and FSMT before converting to a height? Do you add them, subtract them, or compare them another way? • Once you have a net moment value, what must you divide by to end up with just feet, and where do you get that value from the vessel’s data?
• Confirm that both VM and FSMT are in foot-long tons, not in feet. • Be sure you are using the same displacement that corresponds to the stated draft (60.0 feet) from the vessel’s stability data or hydrostatic tables. • After your calculation, check that your final number is a reasonable GM for a large offshore unit (not extremely tiny and not unrealistically huge).
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