Deck General · Free Surface Effect
The free surface correction (FSC) for a tank depends on:
- AThe weight of liquid in the tank and its vertical position
- BThe moment of inertia of the free surface area of the tank divided by the vessel's displacement✓ Correct
- CThe specific gravity of the liquid only
- DThe total number of slack tanks aboard
Explanation
FSC = (i x rho_liquid) / (V x rho_sea), where i is the second moment of area (moment of inertia) of the tank's free surface. Wider tanks have a much larger FSC because i varies with the cube of the width. The weight in the tank does NOT directly determine the correction.
Authority: Stability & Trim (USCG deck topic)
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