Deck General · Cargo Handling & Securing
Free surface effect in a partially filled tank reduces a vessel's effective metacentric height (GM) because:
- AThe liquid adds weight to the keel, raising the center of gravity
- BWhen the vessel heels, the liquid shifts to the low side, increasing the heeling moment✓ Correct
- CWater in a tank increases freeboard and raises the deck edge
- DA slack tank reduces buoyancy, causing the vessel to sit lower
Explanation
Free surface effect occurs when a liquid in a partially filled tank shifts as the vessel heels, creating an additional righting moment on the low side that acts against stability. This effectively reduces GM. The effect is proportional to the cube of the tank's breadth and increases dramatically in wide tanks.
Authority: 46 CFR
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