Load Charts, Capacity, and Rigging Math
Load Charts, Capacity, and Rigging Math
This domain tests chart reading and the arithmetic that turns a chart value into a safe payload. Expect radius, boom length, deductions, parts of line, and percent capacity.
Core rules
- Radius is horizontal distance from the crane's center of rotation to the load's center of gravity, with the boom at the specified length and angle.
- Use the correct chart: outrigger or crawler, boom or jib, quadrant, counterweight, and travel configuration.
- Deduct hook block, slings, shackles, spreader bars, and any attached below-the-hook device. Net capacity = chart capacity − deductions.
- Percent capacity = gross load ÷ chart capacity × 100. Gross load includes all deductions.
- More parts of line increase lifting capacity only within the chart's line-part limits; they do not change structural or stability limits.
Worked example: Chart 18,000 lb at 25 ft radius. Deductions: hook block 450 lb + slings 250 lb + jib 1,200 lb = 1,900 lb. Net allowable payload = 18,000 − 1,900 = 16,100 lb. A 15,500 lb load gives gross = 17,400 lb, utilization = 17,400/18,000 = 96.7%, acceptable only if the chart and site rules allow it.
Traps
- Reading radius to the edge of the load rather than its center of gravity.
- Using the boom-length column for a jib lift.
- Forgetting the jib or stowed attachment deduction.
- Treating line pull as chart capacity.