Rigging, Load Calculation, and Lift Planning
What this domain tests
This domain tests whether you can determine load weight, select and inspect rigging, calculate sling tension, and build a lift plan that controls the load. The exam expects working knowledge of sling configurations, working load limits (WLL), centre of gravity, sharp-edge protection, and critical-lift triggers.
Core rules and concepts
- Identify the load: weight, dimensions, centre of gravity, lifting points, and any attached components.
- Sling configurations change capacity: vertical, choker, basket, and bridle. A choker reduces capacity; a basket can increase it if the D/d ratio and angle are suitable.
- Sling angle matters. Tension rises as the angle from vertical increases. For a two-leg bridle, leg tension = load ÷ (2 × cos(half the included angle)).
- Never exceed the sling's WLL after accounting for configuration, angle, edge protection, and dynamic effects.
- Use shackles and hooks rated for the load; hooks need a functioning latch. Avoid side-loading hooks unless rated.
- A lift plan should identify the crane position, radius, boom length, rigging, signal person, path, exclusion zone, and contingency.
- Critical lifts often include two-crane lifts, loads near capacity, unusual rigging, or lifts over occupied areas; they need a documented plan and supervisor involvement.
Worked example
A 2,000 kg load is lifted with a two-leg bridle. The included angle between the legs is 60°, so each leg is 30° from vertical. Tension per leg = 2,000 ÷ (2 × cos 30°) = 2,000 ÷ 1.732 = 1,155 kg. If each sling has a vertical WLL of 1,500 kg and the configuration is acceptable, the tension is within capacity. If the included angle were 90°, tension would rise to 1,414 kg per leg, leaving little margin.
Traps that cost marks
- Halving the load for a two-leg sling without checking the angle.
- Using the horizontal angle instead of the included angle between legs.
- Ignoring sling weight, shackles, spreader beams, and attached hardware.
- Forgetting that choker use and sharp edges reduce capacity.
- Planning the crane but not the load path or centre of gravity.