Question 66 GLI04 - Mate of LT 500-1600 GRT

The Correct Answer is C. ### Explanation of Correct Option (C) **C) 20 times the wire rope diameter** The Coast Guard, following industry best practices and regulatory standards for safety and longevity of rigging equipment (often mirrored by standards like ASME B30 and ISO standards for marine applications), mandates a minimum sheave diameter. A ratio of **20 times the wire rope diameter (20:1)** is the recognized minimum standard for most continuous-duty applications regulated by the Coast Guard. This ratio is crucial because: 1. **Minimizes Bending Stress:** Bending wire rope around too small a diameter creates excessive bending stress and tension, which significantly reduces the effective strength of the rope. 2. **Prevents Fatigue:** A 20:1 ratio ensures that the individual wires within the rope do not undergo severe metal fatigue (crystallization and breaking) too quickly, maximizing the wire rope's service life and safety margin. 3. **Maintains Strength Efficiency:** Smaller ratios can cause the rope to operate at significantly reduced strength efficiency. The 20:1 minimum helps ensure the wire rope maintains its rated breaking strength during operation. ### Explanation of Incorrect Options **A) 2 times the wire rope diameter:** This ratio is far too small. A 2:1 ratio would cause extreme bending and crushing stress, leading to immediate structural damage, rapid wear, kinking, and catastrophic fatigue failure within a very short operational period. This is dangerously inadequate. **B) Match the rope diameter (1 time):** This is structurally impossible for a wire rope to bend around a sheave with a diameter equal to its own. This would instantly destroy the rope and is never used in any application. **D) 10 times the wire rope diameter:** While 10:1 (or 12:1) is sometimes encountered in low-duty, temporary, or specialized, non-critical applications, it is considered inadequate for the continuous or heavy lifting governed by Coast Guard rules. A 10:1 ratio aggressively shortens the wire rope's lifespan due to increased bending fatigue and does not meet the necessary regulatory minimum standard for critical applications.