The liquid mud tanks on your vessel measure 24'L by 16'B by 8'D. The vessel's displacement in fresh water is 864 tons and the specific gravity of the mud is 1.47. What is the reduction in GM due to a pair of these tanks (p/s) being slack?
• Free surface effect and how a slack tank reduces GM • Formula for free surface moment using tank dimensions (Breadth and Length) • How specific gravity of the liquid affects the GM correction when the vessel is in fresh water
• How do you compute the free surface moment for a rectangular tank using its dimensions, and which dimension is used for the moment of inertia term? • Once you have the free surface moment for one tank, how do you account for a pair of tanks (port and starboard) that are both slack? • How does the specific gravity of the mud compare to fresh water, and how does that ratio change the GM reduction for the same free surface moment?
• Be sure you are using the correct formula for GM reduction: the free surface correction involves moment of inertia / displacement, adjusted for liquid density. • Confirm you are using both tanks in your final calculation (don’t forget to double the free surface effect if appropriate). • Check that your units are consistent: tank dimensions in feet, displacement in tons, and the final GM correction in feet.
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