Load Charts, Capacity, and Rigging Considerations
Load Charts, Capacity, and Rigging Considerations
Load charts are configuration-specific: they depend on jib length, counterweight, rope falls, and whether the crane is fixed or climbing. The rated capacity is the maximum load at a given radius, but the actual capacity may be reduced by rigging weight (hook block, slings, spreader beam). Always subtract rigging weight from the rated capacity to determine the net load you can lift. Radius is measured from the slewing center to the center of gravity of the load (or hook, depending on chart).
Traps: using a chart for the wrong jib length or rope falls; forgetting to include rigging weight; assuming maximum capacity applies at all radii; and misreading metric vs. imperial units. Also, dynamic loads (wind, acceleration) can reduce effective capacity-charts often include a dynamic factor. For multi-crane lifts, each crane's capacity is reduced (often 75% of chart).
Worked example: A crane chart shows 10 t at 20 m radius. Rigging weighs 0.8 t. Net capacity = 10 – 0.8 = 9.2 t. If the load weighs 9.5 t, it exceeds capacity-do not lift. Rule of thumb: Always use the actual radius and actual rigging weight; never estimate.