Load charts, lifting capacity, radius, load estimation and working within rated capacity
Reading load charts
Load charts provide the maximum safe lifting capacity for a given radius and configuration. They are specific to each crane model and setup (e.g., outrigger span, counterweight). The radius is the horizontal distance from the slewing centre to the centre of the load. Capacity decreases as radius increases. Factors such as wind, dynamic loads, and load shape may require de-rating. Always use the chart for the actual configuration; never guess.
Load estimation
Accurately estimate the load weight, including rigging. Use shipping manifests, weighbridges, or calculations. If the weight is unknown, do not lift. The total load must not exceed the rated capacity for the radius. Consider the load's centre of gravity and surface area (for wind).
Traps in questions
A common trap is using the wrong chart for the outrigger configuration. Another is forgetting to include the weight of the rigging and attachments. Also, the chart may be for static conditions; wind or travel may reduce capacity. Do not exceed 75% of capacity for personnel lifts unless specifically permitted.
Worked example / rule of thumb
Example: Chart shows 3 t at 12 m radius. Load weighs 2.8 t, rigging 0.3 t, total 3.1 t > 3 t, so unsafe. Rule: always add rigging weight and check the chart for the exact radius.