Deck General · Blocks & Purchases
A luff tackle uses a double block at the upper (fixed) end and a single block at the lower (moving) end. What is its theoretical mechanical advantage?
- A2
- B3✓ Correct
- C4
- D5
Explanation
Count the rope parts supporting the moving (lower) block. In a luff tackle rigged with the hauling part leading from the single (moving) block, there are 3 parts at the moving block, giving MA = 3. Friction in the blocks reduces actual mechanical advantage to roughly 75-80% of theoretical.
Authority: Deck Seamanship (USCG deck topic)
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