Load Charts
What the exam tests
Load Charts tests your ability to read a capacity chart correctly and to deduct all imposed loads. Expect questions on radius, boom length, boom angle, quadrant, outrigger spread, counterweight and rigging deductions.
Core rules
- Capacity is determined by radius, not by boom length alone. Radius is the horizontal distance from the crane's slewing centre to the load's centre of gravity.
- Read the correct chart for the machine configuration: outriggers fully or partly extended, tyre-mounted, counterweight fitted, jib fitted or not.
- Deduct the hook block, slings, shackles, spreader beam and any attached jib from the gross capacity. The remaining value is the maximum load.
- Check the quadrant and slew limits. A chart may allow more capacity over the rear than over the side.
- Confirm ground bearing under outriggers or tyres. A chart assumes a level, supporting surface.
Worked example
A mobile crane chart shows 18.5 t at a 10 m radius with outriggers fully extended. The hook block and rigging weigh 1.2 t. The net allowable load is 18.5 minus 1.2, or 17.3 t. A 15 t load is acceptable only if the radius remains 10 m and the ground supports the outriggers. If the radius increases to 12 m, the chart must be read again.
Traps
Do not use maximum capacity regardless of radius. Do not ignore rigging weight. Do not use a chart for the wrong outrigger configuration. Do not assume capacity is the same in every direction of slew.
Key points
- Radius controls capacity.
- Deduct hook block and all rigging.
- Use the chart for the actual configuration.
- Check ground bearing and level.