Deck General · Free Surface Effect
A vessel has a calculated GM of 2.0 feet. The total free surface correction for all slack tanks is 0.8 feet. What is the effective GM?
- A2.8 feet
- B1.2 feet✓ Correct
- C0.8 feet
- D2.0 feet — FSC only matters for negative GM
Explanation
Effective GM = GM_solid - FSC = 2.0 - 0.8 = 1.2 feet. The free surface correction acts as a virtual rise of G, reducing effective GM. This is why stability calculations always apply FSC to obtain the true operational GM.
Authority: Stability & Trim (USCG deck topic)
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