Side Capacity at 26 ft with Wind and a Stop Over a Fence
An operator must lift a 3,650 lb valve assembly with 220 lb of slings and shackles. The crane is a 30-ton articulating crane with outriggers fully extended. The boom is at 24 ft, jib stowed. The load is on the ground 26 ft from the rotation center, and the boom will be over the side for the pick and swing. The manufacturer's capacity table for this configuration shows: 25 ft radius, 4,200 lb over side; 30 ft, 3,300 lb over side; 25 ft over rear, 5,200 lb; 30 ft over rear, 4,100 lb. The load has a 30 sq ft sail area and wind is steady at 18 mph. The RCL is set for the side configuration and shows 96% after the load is hoisted. The site foreman says the chart has a 10% margin, so the lift is fine. The load must pass over a 6 ft fence, and the operator plans to stop the swing over the fence to reposition a tag line.
1. Calculate the net load and the interpolated side capacity at 26 ft. Is the lift within chart capacity?
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Net load is 3,650 lb plus 220 lb of rigging, or 3,870 lb. Interpolate between 25 ft and 30 ft over the side: capacity drops from 4,200 lb to 3,300 lb, a decrease of 900 lb over 5 ft, or 180 lb per ft. At 26 ft the interpolated capacity is 4,200 minus 180, or 4,020 lb. The net load is 3,870 lb, which is 150 lb below the chart value, about 3.7% margin. So it is within the static side chart, assuming the radius is measured correctly to the load center and no required deductions were omitted. The foreman's claimed 10% margin does not exist; the actual margin is under 4%.
2. Considering the wind, sail area, and planned stop over the fence, should the operator proceed? Explain the judgment.
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The static chart does not include wind, swing dynamics, or a deliberate stop with the load over a fence. An 18 mph wind on 30 sq ft produces a side force of roughly 25 lb, which is small by itself, but it acts at the load's sail area and can start a swing or side load that the tag line must control. More important, the margin is only 150 lb, and stopping or starting the swing over the fence adds dynamic load. A prudent operator does not proceed on a 3.7% margin. Options are to reposition the crane so the pick can be made over the rear, where interpolated capacity at 26 ft is about 4,980 lb, or to move closer and reduce radius. If neither is possible, wait for lower wind and avoid stopping the load over the fence.
3. What does the RCL reading of 96% tell you, and what should the operator do if the RCL alarms during the swing?
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A 96% reading means the RCL believes the crane is very close to its configured limit; it is a warning to stop and reassess, not a target to approach. The operator should verify the RCL is set for side operation, fully extended outriggers, 24 ft boom, and stowed jib, and should confirm the radius and load. If the RCL alarms during the swing, stop the movement, hold the load, and reduce radius by lowering the boom or repositioning the crane. Do not override or ignore the alarm to finish the swing. Because the static calculation already leaves only 150 lb, any alarm or additional dynamic effect makes continuing unsafe.