About this calculator
A crane's capacity is not one number. The SWL (safe working load) drops as the radius grows: a 40 t ship crane may be good for only 26 t at a 22 m radius. That is why every heavy lift is checked against the crane's load chart at the actual working radius — including the radius when the load is slewed to its final position in the hold or on the barge.
What must be compared with the SWL is the hook load, not just the cargo weight. The calculator adds the cargo weight, the rigging (slings, shackles, spreader bar or lifting beam) and the hook block where the load chart does not already deduct it. For lifts at sea or from ship to barge the load is multiplied by a DAF (dynamic amplification factor) that allows for snatch loads and vessel motion — values of 1.05–1.30 are common depending on conditions and company procedure.
The SWL at radius comes from the load chart table you enter. Conservative mode uses the SWL at the next larger chart radius — most crane manufacturers prohibit interpolation. Linear interpolation is available for comparison. The calculator shows the utilisation, whether it is a critical lift (many procedures use a 75% threshold) and the maximum radius for that load. The radius can be worked out from boom length and angle. This is an education/estimation tool; the official lift plan and the crane and rigging certificates remain the reference.
Worked example
Cargo 32 t, rigging 1.5 t, hook block 0.8 t, DAF 1.10, radius 15 m. Load chart: 10 m 50 t · 14 m 40 t · 18 m 32 t · 22 m 26 t:
- Static hook load 32 + 1.5 + 0.8 = 34.3 t × 1.10 = 37.73 t
- Conservative: 15 m radius → 18 m row → SWL 32 t → 117.9%, not allowed; maximum radius 14 m
- Interpolated: 40 + (32 − 40) × ¼ = 38 t → 99.3% (critical lift), maximum radius 15.1 m
- Conclusion: bring the crane closer to a radius ≤ 14 m or use a larger crane
How to use it
Enter the loads
Enter the cargo weight, rigging weight (slings, shackles, spreader) and hook block if not included in the load chart.
Choose the DAF
Enter the dynamic factor: about 1.0–1.1 for a shore crane at the quay, higher for lifts at sea or ship to barge.
Enter the load chart
Fill radius–SWL pairs from the crane load chart (you can paste a table), then the working radius or boom length and angle.
Read the result
See utilisation, critical lift status and maximum radius; compare conservative and interpolated modes.