What is the D/d ratio of load Houston drums and sheaves?

• A. 18/1
• B. 12/1
• C. 8/1
• D. 24/1

Answer: (A)

The D/d ratio expresses drum diameter divided by rope diameter. It determines how gently the rope bends when it wraps around the drum or passes over a sheave. A larger ratio means the rope experiences a gentler bend, which lowers bending stress, reduces groove wear, and extends rope life, contributing to safer, more reliable hoisting.

For load hoisting drums and sheaves, a common, recommended practice is a drum diameter about 18 times the rope diameter, giving a D/d ratio of 18:1. This size provides sufficient wrap around the drum to avoid sharp bends while keeping the drum practical in size. Smaller ratios would force the rope into tighter bends, increasing wear and fatigue; much larger ratios, while safe, are typically not necessary for standard equipment.