The DEEP DRILLER, at 60.0 feet draft in sea water, has VM = 974,441 foot-long tons, LM = 40,301 foot-long tons, TM = 3 foot-long tons, FSML = 30,572 foot-long tons, and FSMT = 18,732 foot-long tons. What is the longitudinal free surface correction to KG?
• Free surface effect and how it changes the vessel’s centers of gravity (transverse vs longitudinal) • Relationship between free surface moment (FSM) and corrections to GM or KG • Difference between initial GM/VM/LM/TM and the correction applied to KG
• Which of the given values (VM, LM, TM, FSML, FSMT) relate to longitudinal stability and which to transverse stability? • How do you convert a free surface moment into a correction to KG – are you adding or subtracting, and what must you divide by? • Does a longitudinal free surface correction usually affect trim, overall KG, or both – and how is that handled in drilling unit stability calculations?
• Identify which FSM is longitudinal (FSML) and make sure you pair it with the correct moment of inertia term (LM, TM, or VM) • Confirm the units on all quantities (foot-long tons, feet, long tons) and ensure the correction result comes out in feet • Check whether the correction for longitudinal free surface to KG is typically small or large compared to transverse corrections, to help you judge which multiple-choice options are reasonable
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