Load Charts, Rigging, and Lifting
What the exam tests
Reading manufacturer load charts, calculating capacity at radius, and rigging loads so the rig, rope, and hardware are not overloaded. The exam favors the chart for the exact rig configuration over remembered crane numbers.
Core rules
- Capacity comes from the drill rig manufacturer's chart for the exact configuration: mast or boom angle, radius, outrigger spread, counterweight, reeving, and line pull. Never substitute a mobile crane chart.
- Radius is horizontal distance from rotation center to hook or load center. Measure with the load hanging free, not with the mast pulled over.
- Deduct the load block, slings, shackles, and auxiliary equipment from gross capacity to get net allowable load.
- Rigging: determine center of gravity, sling angle, tension, and hardware ratings. Use tag lines to control rotation without side-loading the mast.
- The weakest component controls: wire rope, line pull, hook, shackle, sling, or structure.
Worked example
A 10,000 lb load is lifted with a two-leg bridle, each leg 60° above horizontal. Vertical share per leg = 5,000 lb. Tension = 5,000 / sin 60° = 5,773 lb per leg. At 30°, tension = 5,000 / sin 30° = 10,000 lb per leg-double. Verify slings and shackles for the higher tension, not the vertical share.
Traps
Using included angle instead of angle to horizontal; reading capacity at the wrong radius; forgetting block and sling weight; assuming short outriggers are acceptable; shock loading a rig at its chart limit.