The fleet angle limit on a smooth wire rope drum is given as either a degree or a ratio. Which is correct?

The fleet angle limit on a smooth wire rope drum is given as either a degree or a ratio. Which is correct?

• A. 3 degrees or 60:1
• B. 1 1/2 degree or 40:1
• C. 2 degrees or 20:1
• D. 0.5 degree or 10:1

Answer: (B)

The fleet angle is the angle at which the rope leaves a smooth drum, and keeping it small reduces rope wear and improper bedding in the groove. This limit is commonly stated in two equivalent ways: as a small angle, about 1.5 degrees, or as a drum-to-rope diameter ratio of about 40:1. They’re the same limit because, for small angles, tan(theta) is roughly theta in radians, so a fleet angle of about 1.5 degrees corresponds to a drum diameter roughly 40 times the rope diameter (tan(1.5°) ≈ 0.026, close to 1/40). Therefore both expressions convey the same constraint.

The fleet angle is the angle at which the rope leaves a smooth drum, and keeping it small reduces rope wear and improper bedding in the groove. This limit is commonly stated in two equivalent ways: as a small angle, about 1.5 degrees, or as a drum-to-rope diameter ratio of about 40:1. They’re the same limit because, for small angles, tan(theta) is roughly theta in radians, so a fleet angle of about 1.5 degrees corresponds to a drum diameter roughly 40 times the rope diameter (tan(1.5°) ≈ 0.026, close to 1/40). Therefore both expressions convey the same constraint.