Load Charts, Capacity, and Load Calculations
Reading a crawler crane load chart is a core skill. Charts are organized by boom length and configuration (main boom, boom plus jib, luffing jib), then by radius, with boom angle shown for reference. Candidates must know how to enter the chart: use the actual radius, round up to the next tabulated radius if the value falls between lines, and never interpolate upward. Use the lowest capacity among all applicable limits, including boom strength, tipping, jib, and any footnote restrictions.
Deductions are the most common trap. Subtract the hook block, slings, shackles, spreader bars, and any stowed or erected jib or auxiliary boom head from the chart value to get net allowable load. Some charts list capacity for a specific hook block; using a heavier block reduces capacity. Parts of line must be sufficient for the load: required parts = load divided by the single-line pull, rounded up, and the chart may specify a minimum or maximum number of parts.
Other traps: using the wrong boom length column, ignoring a footnote that reduces capacity for a jib stowed on the boom, forgetting that some charts require the boom to be at a minimum angle, and confusing gross and net capacity. Also remember that the load's center of gravity, not the hook, defines radius when the load hangs off-center.
Worked example: chart shows 30,000 lb at 40 ft radius with 100 ft boom. Hook block is 1,500 lb and rigging is 500 lb. Net allowable load is 30,000 minus 2,000 = 28,000 lb. If the load weighs 27,500 lb, the lift is acceptable (within chart), but confirm parts of line and wind limits.