Load Chart Use and Capacity Determination
Gross capacity is not allowable load
Load charts give gross capacity for a specific radius, boom length, angle, quadrant, outrigger condition, counterweight, and parts of line. To find the allowable load, subtract from gross capacity everything that hangs from the boom: hook block or ball, slings, shackles, spreader bars, buckets, and personnel platform. Then compare the result to the actual load weight. Confirm the chart's radius definition and area of operation. Structural and stability limits both matter; the lower one governs. Interpolation may be allowed only where the manufacturer permits it.
Traps
Using boom length where radius is required; measuring radius to the load instead of to the hook; using a full-outrigger chart with partial outriggers; forgetting hook block and rigging deductions; reading the wrong column for quadrant or boom mode; and assuming a chart for one crane applies to another. Remember: adding parts of line does not increase chart capacity-the chart already assumes a configuration.
Worked example
Gross chart capacity at the actual radius is 12,000 lb. The hook block weighs 600 lb, and slings plus shackles weigh 300 lb. Allowable load = 12,000 − 900 = 11,100 lb. A 10,500 lb load is acceptable; an 11,300 lb load is not.