Load Chart at Radius with a Pole and Crosswind
A crew is using a digger derrick with a 50 ft boom and stowed jib to lift a 42 ft, 2,900 lb treated pole. Rigging, slings, and a pole grab add 250 lb, so the suspended load is 3,150 lb. The operator measures 22 ft from the center of rotation to the load hook. The load chart in the cab, for outriggers fully extended and the jib stowed, lists 3,400 lb at 22 ft, 3,050 lb at 24 ft, and 2,850 lb at 26 ft. The lift must clear a 6 ft fence, and a 12 mph crosswind is forecast. The operator plans to boom up until the pole clears, then swing 90 degrees. A less experienced ground hand will tail the pole with a tag line. The operator says the chart is close enough because the load is under the 22 ft rating.
1. Is the lift acceptable at the measured 22 ft radius? Show the capacity check and the margin.
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At the measured 22 ft radius, the chart capacity is 3,400 lb and the suspended load is 3,150 lb. The load is under capacity by 250 lb, or about 7 percent. That is technically within the chart at that exact radius, but the margin is small and the chart value assumes the correct configuration: outriggers fully extended, jib stowed, proper boom length, and no dynamic or wind effects. The operator should not treat 'under the 22 ft rating' as the end of the analysis. The next step is to ask whether 22 ft will remain the actual radius during the lift. If the radius grows, the capacity falls quickly: at 24 ft the rating is 3,050 lb, which is below the 3,150 lb load.
2. What operating conditions could change the actual radius, and how should they be controlled?
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Radius can increase from boom deflection under load, swinging the pole, wind pushing the pole, tag-line pull, and the ground hand allowing the pole to drift outward. The 12 mph crosswind acting on a 42 ft pole can create significant side load and sway, especially during the 90 degree swing. Control measures include keeping the load as close to the machine as practical, using a tag line operated by a trained hand who pulls only to control rotation and never to move the load outward, avoiding sudden starts and stops, and monitoring the radius indicator or measured hook position throughout the lift. If the pole must clear a 6 ft fence, reposition the machine or use a different lift plan so the required boom-up does not push the load beyond the chart radius.
3. If the radius grows to 24 ft before the pole clears the fence, what should the operator do?
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At 24 ft the capacity is 3,050 lb, so the 3,150 lb load is over the chart by 100 lb. The operator must stop the lift and lower the pole to a safe position, then reduce the radius before continuing. Options include repositioning the machine closer to the pole, changing the lift point or boom angle, removing unnecessary rigging weight, or using a machine with a higher capacity at that radius. The operator should not continue simply because the overload is small; load charts are limits, not targets. After repositioning, re-measure the radius with the load applied, confirm the chart configuration, and brief the ground hand on tag-line control before restarting.