Load Charts and Capacity Determination
Load Charts and Capacity Determination
Boom-truck charts are not a single capacity number. They are families of ratings by outrigger condition, boom length, radius, quadrant, jib configuration, and counterweight. The written exam tests chart literacy: selecting the correct column and notes, applying deductions, and recognizing that the lowest limit-structural, stability, or wire rope-controls.
Core rules
- Read the chart title and notes first: outriggers fully extended vs retracted, “on tires,” boom length, jib stowed or deployed, and allowable quadrants.
- Radius is measured from the boom pivot center to the vertical hoist line, with the boom at its working position-not from the carrier bumper.
- Deduct hook block, headache ball, slings, shackles, jib or attachments, and any chart-required allowance from chart capacity to get net allowable load.
- Do not interpolate between radii or boom lengths unless the chart explicitly permits it; use the next longer radius or shorter boom.
- Capacity may be limited by wire rope, boom strength, or tipping. Never average two ratings.
Worked example
At 30 ft radius with outriggers fully extended, the chart shows 9,000 lb. Notes require a 500 lb deduction for the stowed jib. Hook block is 350 lb and rigging is 250 lb. Net allowable = 9,000 − 500 − 350 − 250 = 7,900 lb. A 7,500 lb load is acceptable on paper, but only if radius stays at or below 30 ft and the correct outrigger and boom configuration is actually set. If the operator telescopes out, the new radius may reduce capacity below 7,500 lb.
Traps
Reading across the wrong boom-length row; using the retracted-outrigger column after full extension; forgetting the jib deduction; measuring radius to the load’s near edge; and treating a chart’s maximum capacity as available at every radius.