Load Charts, Capacity Determination, and Rated-Load Calculations
The chart is the authority
A rated load is never simply the weight you may pick - it is the gross load the crane can handle in a specific configuration, including everything hanging below the boom tip. Candidates must read radius, boom length, boom angle, boom/jib combination, quadrant (over front, side, or rear), outrigger beam extension, counterweight, and parts of line, and must know which chart row matches the machine as it is actually set up.
Gross versus net capacity
Net allowable load = chart capacity minus the weight of the load block or overhaul ball, hook, slings, shackles, spreader beams, and any jib or attachment not already reflected in the chart. Doing the subtraction in the other order (rigging from load weight) produces the same number but invites errors on multi-part picks.
Traps that appear in questions
- Measuring radius from the boom pin instead of the center of rotation.
- Reading the capacity at the next shorter radius, or rounding the radius down.
- Using an on-rubber or pick-and-carry chart when the crane is on outriggers, or vice versa; on-tire capacity is far lower and travel under load is often prohibited.
- Missing that the governing limit may be structural (outriggers) or stability (tires) - the lower value always controls.
- Mixing tons and pounds, or forgetting the jib is erected and stowed.
Worked example
Chart shows 12,400 lb at 25 ft, full outriggers, over the side. Block and hook weigh 400 lb; slings and shackles 700 lb. Allowable load = 12,400 − 1,100 = 11,300 lb. A 10,900 lb load technically fits, but a 400 lb margin is thin - verify the actual radius on the load moment indicator before the pick.
Rule of thumb: when in doubt, use the next longer radius and the next shorter boom length.