Crane Hook Rotation: Causes and Preventive Measures

Hook rotation often occurs unexpectedly during lifting operations. When a crane hoists a load, the hook may start rotating, causing the wire rope between the hook and the boom head sheave to twist. As a result, the suspended load rotates with the hook, making further hoisting or lowering impossible. This phenomenon disrupts operations and poses serious safety risks to personnel and equipment, making prevention essential.

Causes of Hook Rotation

Hook rotation stems from both internal and external factors, with internal causes being the root issue.

1. Internal Factors (Wire Rope Torque)

All wire ropes—regardless of type, specification, or grade—generate torque under load due to their construction:

• Manufacturing Process: Individual wires are twisted into strands, which are then helically wound to form the rope. When tensioned, the wires and strands tend to straighten, but since the rope ends are fixed, internal torque builds up.
• Rope Aging: Over time, the rope’s lay length (pitch) increases, creating residual torque even when unloaded. This torque induces rotational forces in the hook assembly.

2. External Factors

• Human or wind-induced forces pushing the hook during lifting.
• Unstable operator maneuvers causing hook/swing oscillations.
• Improper rope reeving leading to hook imbalance.

Key Influencing Factors

1. Crane Size: Taller cranes (longer wire ropes between boom tip and hook) increase rotation risk.
2. Rope Reeving: Odd-numbered reeving is more prone to rotation than even-numbered. Fewer parts of line exacerbate the issue.
3. Load per Rope: Higher tension on individual ropes raises rotation likelihood.
4. Hook Design: Smaller hook blocks/sheaves are more susceptible.
5. Operator Technique: Jerky hoisting/lowering motions, especially during load liftoff, amplify rotation.

Post-Rotation Solutions

If the hook rotates and ropes twist:

Reattach the rope and cycle the hook several times at maximum boom angle to verify stability.

For Low Heights: Lower the load via luffing (if crane permits), then manually untwist the hook.

For High Heights: Maneuver near a structure to stabilize the hook.

Torque Release:

Ground the hook, detach the rope’s fixed end.

Rotate the free end opposite to the rope’s lay direction by k = m × n turns (*m*: hook rotations; *n*: rope parts). Adjust as needed.

Preventive Measures

1. Sheave Selection: Use outermost sheaves on multi-sheave hooks/booms where possible.
2. Hook Size: Prefer hooks with larger-diameter sheaves.
3. Rope Reeving: Opt for even-numbered and more parts of line to distribute load.
4. Alignment: Minimize offset between boom tip and hook sheaves to reduce rotational forces.
5. Rope Length: Shorten the rope span (e.g., use wider outrigger spreads).
6. Taglines & Locks: Employ taglines for load control; use hook locks for non-rotational lifts.
7. Smooth Operation: Avoid simultaneous hoisting/rotation motions.
8. Rope Type: Select rotation-resistant ropes when feasible.
9. Maintenance: Periodically re-reeve ropes or release fixed-end torque.