Your vessel displaces 368 tons and measures 96'L x 28'B. You ship a large wave on the after deck. What is the reduction to GM due to free surface before the water drains overboard, if the after deck measures 42'L x 28'B and the weight of the water is 36 tons?
⢠Free surface effect (FSE) and how it reduces GM (metacentric height) ⢠Using the second moment of area of a rectangular tank (or deck area) for free surface moment: I = (L à B³) / 12 ⢠Relationship between free surface moment, displacement, and the reduction in GM
⢠How do you convert the deck dimensions (42 ft Ć 28 ft) into the free surface moment using the correct formula for a rectangular area? ⢠Once you have the free surface moment, how is it divided by the vesselās displacement (368 tons) to obtain the reduction in GM? ⢠Where (if at all) does the given 36 tons of water weight actually matter in calculating free surface reduction for a wide, slack surface?
⢠Confirm you are using B³ (breadth cubed) and not length cubed in the free surface formula. ⢠Make sure the displacement used in the denominator is the vesselās total displacement (368 tons), not the 36 tons of shipped water. ⢠Check that all units are consistent: deck dimensions in feet, displacement in tons, and that your result for GM reduction is in feet.
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