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 KG corrected for transverse free surface effects?
• Free surface effect (FSE) and how it creates a virtual rise in KG • Difference between initial KG and corrected KG (KG with free surface) • How to use FSMT (transverse free surface moment) together with ship’s displacement to find the rise in KG
• First, think about which quantities given are related to transverse stability and which are related to longitudinal stability. Do you need FSMT or FSML for this question? • Ask yourself: to correct KG for free surface, do you ADD or SUBTRACT the free surface correction from the original KG? Why? • Once you have the free surface correction in feet, how do you combine it with the original KG to get the new, corrected KG?
• Identify or calculate the vessel’s displacement in long tons before using FSMT. Without displacement, you cannot get the rise in KG. • Be sure you are using consistent units: FSMT is in foot-long tons; the correction to KG must be in feet. • Double-check that you applied the free surface correction in the correct direction (does FSE make the ship more or less stable?).
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