Rigging, sling and hardware selection, and load handling
Domain 2 tests selection and use of slings and hardware, plus control of the load from pick to set. Expect questions on tension, angle, derating, inspection, and hardware compatibility.
Selection rules
- Establish load weight and center of gravity before choosing gear. Unknown weight is a stop.
- Match sling type to load: chain for abrasion, wire rope for heavy or rugged service, synthetic web or round for soft or finished loads, with edge protection.
- Use the configuration WLL: vertical, choker, basket, and multi-leg efficiencies differ. Do not exceed hook or master link rating.
- Hooks need latches; shackles need correct pin and bow orientation; avoid side loading.
Tension and angle
For a symmetrical two-leg bridle, leg tension = load / (2 x sin of angle from horizontal). Lower angle means higher tension. At 60 degrees, tension is 0.577 x load per leg; at 45 degrees, 0.707 x load; at 30 degrees, 1.0 x load.
Worked example
A 10,000 lb load on a two-leg bridle at 60 degrees from horizontal: each leg carries 10,000 / (2 x 0.866) = 5,774 lb. Select a sling with a configuration WLL at least 5,774 lb, not the vertical rating. If the angle is reduced to 45 degrees, tension rises to 7,071 lb per leg; the same sling may now be overloaded. Add edge protection and check the master link and hook for the total load.
Traps
Using the angle from vertical; treating a choker as vertical capacity; mixing sling types; no softeners; assuming a latch is a load-bearing feature; using damaged or unmarked gear; letting the load slide or drag.