On a vessel of 6500 tons displacement, a tank 30 ft. long, 32 ft. wide and 15 ft. deep is half filled with oil cargo (S.G. 0.948) while the vessel is floating in saltwater (S.G. 1.026). What is the free surface constant for this tank?
⢠Free surface effect and how it reduces stability ⢠Formula for the second moment of area (I) of a rectangular free surface: I = (l à b^3) / 12 ⢠How specific gravity (S.G.) of the liquid vs. seawater affects the correction/constant
⢠Identify which tank dimension is athwartships (breadth) and which is foreâandâaft (length) for the free surface calculation ⢠Recall whether the depth of liquid (full vs. half full) changes the free surface moment of inertia for a rectangular tank ⢠Think through how to adjust the result for the liquid S.G. (0.948) compared to saltwater S.G. (1.026) before using the vesselâs displacement
⢠Be sure you are using bÂł (breadth cubed) in the I = (l Ă bÂł)/12 formula, not lÂł ⢠Confirm that displacement (6500 tons) is in the same system of units as the free surface constant youâre calculating ⢠Apply the S.G. ratio (liquid / seawater) at the correct stage of your calculation before comparing to the multipleâchoice answers
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