How do you determine the maximum allowable load for a given boom length and radius using the load chart?

• A. Apply a fixed safety factor and use the general crane rating irrespective of configuration.
• B. Use the longest possible capacity regardless of length or radius.
• C. Ignore wind and derating factors.
• D. Locate the boom length on the vertical axis and the radius on the horizontal axis; read the capacity value at their intersection; apply deratings for nonstandard configuration, indirect lifts, or wind; ensure the load plus rigging is within the rating.

Answer: (D)

Understanding how a load chart works is essential for safe lifting. The chart encodes how a crane’s capacity changes with its geometry: the boom length and the radius determine the tipping moment and how much counterweight is effective. So you don’t just pick a single number; you read the capacity that corresponds to the exact configuration you’re using.

To determine the maximum allowable load, you locate the given boom length on the vertical axis and the radius on the horizontal axis, then read the capacity value at their intersection. That number is the maximum load for that exact configuration. But it isn’t the end of the check. You must apply deratings for nonstandard configurations (such as using a jib or unusual rigging), indirect lifts, or wind, and you must include the rigging weight in the total. The adjusted rating must still be greater than or equal to the load plus rigging; otherwise the lift is not permitted.

This approach is necessary because a crane’s capacity isn’t fixed—it decreases as you reach farther (larger radius) or extend the boom (longer length), and it must be adjusted for other factors to ensure stability and safety.