The liquid mud tanks on your vessel measure 32'L by 15'B by 8'D. The vessel's displacement is 640 tons and the specific gravity of the mud is 1.8. What is the reduction in GM due to a pair of these tanks (p/s) being slack?
• Free Surface Effect (FSE) and how it reduces GM • Formula for free surface moment in a rectangular tank: breadth, length, and liquid properties • Effect of multiple slack tanks and specific gravity on virtual rise of G
• How do you compute the free surface moment of one rectangular slack tank, and how does that change when you have a port and starboard pair? • Once you have total free surface moment, how is the reduction in GM related to this moment and the vessel’s displacement? • Where does the specific gravity of the mud enter the calculation—does it change volume, density, or both in your formula?
• Be sure you are using moment of inertia of the free surface area, not the volume of the tank • Confirm that the tank dimensions used in the calculation correspond to the free surface area (which sides form the surface?) • Verify that displacement is in consistent units with your free surface moment, and convert if necessary before finding ΔGM
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