While the COASTAL DRILLER is in transit at a draft of 10 feet 6 inches, a severe storm is predicted within 12 hours. VM are 546,462 ft-kips, FSML are 18,000 ft-kips, and FSMT are 32,000 ft-kips. How much should the KG corrected for free surface effects be lowered to satisfy the maximum allowable KG criteria?
• Free surface effect (FSE) and how it changes the vessel’s effective KG • The relationship between virtual GM, maximum allowable KG, and FSML / FSMT • How to convert moment values (ft-kips) into a change in KG
• Start by thinking: if you remove the free surface effect, does KG effectively go up or down? How does that relate to stability? • Consider how you would combine FSML and FSMT to get a total free surface moment and then relate that to the vessel’s displacement to find a KG correction. • Ask yourself: are you being asked for the final KG or for the amount of reduction in KG needed to meet the criteria?
• Be clear whether VM (546,462 ft-kips) is a vertical moment related to KG, not a weight or displacement by itself. • Verify that you convert kips to long tons or pounds consistently so units match when you form any ratio to get KG. • Double-check whether you should be using FSML + FSMT together or only one of them for the condition described.
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