Rigging and Load Handling
Rigging questions test whether you can select and inspect gear, determine load weight and center of gravity, and predict how sling angle affects tension. Know the common hitch types-vertical, choker, basket, and bridle-and that each has an efficiency factor relative to a vertical hitch. Understand that as the horizontal sling angle decreases, tension in each leg increases sharply, and that the load's center of gravity governs how it hangs and whether it will tilt when lifted.
Key concepts include working load limit versus breaking strength (with the design factor applied), matching shackles and hooks to the load, using softeners at sharp edges, and controlling load rotation with tag lines. Know that tag lines keep the load from spinning but must never be used to control a load that is beyond the rigger's ability to manage, and that personnel must not stand under or in the path of a suspended load.
Traps: assuming two slings share load equally regardless of geometry; using a choker rating as if it were a vertical rating; forgetting that a basket hitch doubles capacity only when legs are near vertical; and ignoring the effect of an off-center center of gravity. Another trap is treating a damaged sling as usable if the damage is away from the tag.
Rule of thumb: tension per leg equals (load ÷ number of legs) ÷ sin of the horizontal angle. At 30 degrees, each leg carries the load of a vertical hitch divided by 0.5-double the naive share.
Worked example: a 2,000 lb load in a two-leg bridle at 30 degrees horizontal. Naive share is 1,000 lb per leg; dividing by sin 30° (0.5) gives 2,000 lb per leg. Select slings rated for at least that tension.