A vessel's stability is greatly reduced by liquid free surface. Which of the listed conditions would develop the greatest adverse effect?
Official USCG Answer & Rule Citation
Correct Answer: Option C — Tanks which are 40% full.
Free surface effect is greatest when the liquid surface area is largest, which occurs when tanks are partially filled. A tank 40% full allows the liquid to shift significantly as the vessel rolls, creating a large virtual rise in the center of gravity and reducing stability.
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