Load charts, lifting plans, and capacity calculations
This is the numeracy domain. You must read the manufacturer's chart correctly, deduct everything hanging below the hook, and prove the pick is inside capacity.
Reading the chart
- Locate the correct configuration first: jib length, counterweight, reeving or parts of line, and whether the crane is free-standing, tied-in, or on a rail base.
- Radius is horizontal distance from the slew centre to the load's centre of gravity at the moment of the lift, with the jib deflected.
- Never interpolate beyond printed rows; if the radius falls between two rows, use the longer radius and lower capacity.
- Two-crane lifts apply the planner's reduction, commonly 75–80% of each crane's single-crane capacity, plus a shared-load diagram.
Net capacity
Net capacity = chart (gross) capacity − hook block − slings − shackles − spreader beam − any attachments. Only the remainder can be load.
Worked example
Chart gross at 24 m: 9.0 t. Hook block 0.40 t, four-leg sling set 0.12 t, shackles 0.06 t. Net = 9.0 − 0.58 = 8.42 t. The load weighs 8.0 t, so utilisation is 8.0 ÷ 8.42 = 95% - legal but tight, so a planner would re-check set-down radius, ground bearing, and wind area before approving. At 26 m the chart shows 7.8 t gross, net 7.22 t, and the same lift would be rejected.
Traps
Using the capacity in the wrong column; mixing pounds and kilograms; forgetting rigging deductions; checking only the pick radius; assuming a bigger counterweight raises capacity without re-reading the chart.