Mid-Span Outriggers and a Chart That Does Not Apply
A 60-ton all-terrain crane must set an 18,000 lb generator at a 45 ft radius, over the front of the carrier. The only setup spot is a 14 ft wide driveway. The manufacturer's full outrigger spread is 22 ft beam-to-beam, and the beams must be pinned either at full extension or at the published 50% mid-span position. Full spread means closing a public street for four hours. Counterweight is 10,300 lb, the boom is pinned at 47 ft, and the jib is stowed. The estimator's note reads: "Chart says 21,000 at 45 ft, 3,000 lb to spare." The mid-span chart rates 15,000 lb at 45 ft and is a 360° chart. Hook block is 550 lb; rigging is 300 lb.
1. Is the 3,000 lb margin real? Which chart governs and why?
Read the worked answer
No. The 21,000 lb figure is the full-spread chart. In a 14 ft driveway the beams cannot reach the full position, so that chart describes a crane you do not have.
Governing chart: the mid-span (50%) chart for the same boom length, counterweight, and area of operation, i.e., 15,000 lb at 45 ft.
Deductions: hook block 550 + rigging 300 = 850 lb. Net available = 15,000 − 850 = 14,150 lb against an 18,000 lb load. That is roughly 3,850 lb short, about 27% over the rated capacity.
The structural point: an outrigger beam has no rating between the published pin positions. You cannot extend it "most of the way" and interpolate, and the rated capacity limiter has no configuration setting for a position the manufacturer never published. The RCL must be set for mid-span, and the chart that matches it is the one you lift from. If the RCL is left set for full spread, the system will allow a lift the machine's actual footprint cannot support.
2. What realistic options would make this lift legal and safe?
Read the worked answer
Three routes, each with a check:
- Full spread. Close the street, extend and pin both beams fully. Net capacity = 21,000 − 850 = 20,150 lb against 18,000 lb, about a 12% margin. Before committing, verify the ground or street structure under the floats can take the higher outrigger reactions at full spread, and check for buried utilities under the roadway.
- Reduce radius on the mid-span chart. Capacity has to be ≥ 18,850 lb gross to leave 18,000 lb net. Find the radius on the mid-span chart where the rating meets that (likely in the high 30s of feet) and reposition the carrier or the load to achieve it. Measure that radius from the rotation center to the load line with the boom in the lift position, not to the edge of the load.
- Change the crane or the plan. A larger machine, or splitting the generator into components that can be set at a shorter radius.
What is not a route: shortening the boom alone. At a 45 ft radius on a stability-limited chart, boom length barely moves the number, and the outrigger configuration still governs.
3. Before the pick, what configuration items must be confirmed against the chart?
Read the worked answer
The chart is only valid for the exact machine in front of you:
- Outriggers: both beams pinned at the same published position, lock pins seated, floats attached and fully bearing on pads, no voids. Tires just clear of the ground.
- Level: verified in two directions with a level, within the manufacturer's tolerance, not judged by eye.
- Counterweight: correct amount for the chart, fully seated, retaining pins in.
- Boom: pinned length matches the chart column; telescoping mode (e.g., full-power pinning) matches the chart's assumption.
- Jib/fly/auxiliary head: stowed and deducted per the notes, or erected and the jib chart used instead.
- Rated capacity limiter: set to the actual configuration, functioning, and calibrated within the required interval; anti-two-block device operational.
- Load chart: the one on the machine matches that serial number and configuration, and includes the notes page.
- Exclusion zone: barricaded so nobody walks or stands between the outrigger beams.