Load charts, capacity calculations, and lift planning
Load charts, capacity calculations, and lift planning
This domain tests the numbers: reading the right column, deducting rigging, and building a lift plan that is provably within capacity.
Reading the chart
- Columns are boom length (lattice) or boom angle, rows are radius, cells are rated capacity. Charts are configuration-specific: counterweight, 360° swing vs. over-end, static vs. pick-and-carry, jib fitted.
- Radius is measured horizontally from the centre of rotation to the centre of gravity of the load, with the boom deflected under load. Do not measure to the near edge of the load.
- Never interpolate between boom lengths; use the next longer boom length. For a radius between two rows, use the longer radius (lower capacity). Never extrapolate.
- Deduct everything below the hook that the chart notes do not already include - slings, shackles, spreader beams, jib or auxiliary head where required. Read the chart's own notes to confirm what is included.
- Check parts of line: available line pull can govern before the chart value does.
- Typical critical-lift thresholds: over 75% of chart capacity, multi-crane, personnel, or near power lines - these need an engineered plan.
Worked example
Boom options are 30 m and 36 m; your boom is 33 m. Radius is 11.2 m; the 36 m column gives 7.2 t at 12 m. Deduct 0.3 t of slings → 6.9 t usable. A 6.5 t load uses 94% of capacity, so the lift is critical and needs a documented plan and supervisor sign-off.
Traps
Interpolating between boom lengths; ignoring chart notes; mixing feet and metres; forgetting whether the hook block is included; planning to 100% with no margin.