Deck General · Free Surface Effect
A vessel has two identical slack fuel tanks side by side. Installing a centerline watertight division in each tank (creating four narrower tanks) will reduce the total free surface effect by approximately:
- A25%
- B50%
- C75%✓ Correct
- DThe FSE doubles because there are now more tanks
Explanation
The moment of inertia of a rectangular tank varies with width cubed (i = l x b^3 / 12). Halving the width of each tank reduces each tank's i to 1/8. Two half-width tanks together have 2 x (1/8) = 1/4 of the original i, reducing FSC by 75%.
Authority: Stability & Trim (USCG deck topic)
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