Tight Capacity Calculation, Expired Certification, and Hands on the Load
A 150 t crawler crane is lifting a 9.4 t vessel with a 54 m main boom at 30 m radius, 360° swing. The load chart shows 12.0 t at 30 m for the 54 m boom. The hook block weighs 0.65 t, the slings and shackles 0.35 t, and a 0.20 t spreader beam is used. The crane is on firm ground with mats. The operator plans to lift, swing 180°, and set the vessel on a foundation 2.5 m below grade. The site has a 25 m exclusion zone, but the client wants two fitters to guide the vessel by hand at the foundation because the tag lines are tangled. The LMI shows 98% of capacity during the trial lift. The crane's load test certificate expired three months ago. The sling certificate is available, but the shackle is unmarked. The lift is scheduled in 30 minutes.
1. Calculate the gross load and net capacity, and decide whether the lift can proceed.
Read the worked answer
Gross load = 9.4 + 0.65 + 0.35 + 0.20 = 10.6 t. Net capacity = 12.0 - 0.65 - 0.35 - 0.20 = 10.8 t. Utilization = 10.6 / 10.8 = 98.1%.
So the load is within the chart by only 0.2 t. That is not a comfortable margin: dynamic starts and stops, wind, out-of-level ground, or a radius increase can push it over. More importantly, the lift is not acceptable as planned because:
- The crane's load test certificate expired three months ago; the crane must be current before use.
- The shackle is unmarked; its WLL cannot be verified.
- Two fitters are intended to guide the load by hand inside the exclusion zone.
Stop the lift. Verify or renew the load test, use marked certified rigging, and keep all personnel out from under the load. Recalculate with the actual verified rigging weights.
2. Explain the effect of the 360° swing and the below-grade set on the capacity and load control.
Read the worked answer
Use the 360° chart. If the chart has a higher 'over-end' or 'over-side' value, it cannot be used for a 180° swing. The lift must stay within the 360° rating for the actual boom length and counterweight.
For the below-grade set: with a vertical load line, lowering the load does not change the horizontal radius, so the 30 m radius remains valid if the boom tip stays directly above the load. But if the foundation is offset or the load line is pulled sideways, the radius changes and side load is introduced. The operator must keep the load line vertical, lower slowly without free fall, and confirm boom tip clearance and wire rope verticality. The exclusion zone must extend around the pit, and the signal person must have a clear view of the load and the foundation. Do not let fitters stand in the pit under the load.
3. What documentation should be verified before the lift and completed after it?
Read the worked answer
Before the lift, verify and file:
- Crane annual inspection and current load test certificate.
- LMI calibration and function test, including anti-two-block.
- Operator's valid NC III certificate and medical or authorization.
- Rigging inspection certificates and marked WLL for slings, shackles, and spreader.
- Lift plan with chart page, gross load calculation, radius, boom configuration, ground conditions, and exclusion zone.
- JSA or risk assessment, permit, and pre-lift meeting attendance.
After the lift, record in the logbook: date, load, radius, boom configuration, chart used, actual duration, any defects, and sign-off. If the lift is stopped, write the reason, tag the crane, notify the owner and client, and retain the defect report. Do not alter the lift plan after the fact; issue a revision.