Load Calculations & Capacity Planning
Calculating gross and net capacity, parts of line, line pull, rigging weight deductions, and design safety factors.
- Calculate net capacity from gross capacity by applying all deductions
- Explain parts of line and calculate line pull
- Determine load weight using drawings, tags, and volume calculations
- Apply wire rope safety factors to verify safe operation
Lección 1
Gross Capacity, Net Capacity & Deductions
Understanding the Difference
The load chart provides gross capacity - the total weight the crane can support at a given radius and boom length. But this is not the weight of load you can actually pick up. You must subtract everything between the boom tip and the load to find the net capacity - the actual weight of load you can safely lift.
Calculating Net Capacity - Example
Consider a lift where the chart shows 50,000 lbs gross capacity at the planned radius:
| Item | Weight |
|---|---|
| Gross capacity from chart | 50,000 lbs |
| Minus hook block | -1,200 lbs |
| Minus four slings | -400 lbs |
| Minus shackles | -120 lbs |
| Minus spreader bar | -2,500 lbs |
| Net capacity (available for load) | 45,780 lbs |
If the actual load weighs 44,000 lbs, the lift is within capacity. If the load weighs 46,000 lbs, the lift exceeds net capacity and cannot be made at that radius.
Every Pound Counts
All weight below the boom tip counts against capacity - including the hook block, headache ball, rigging, slings, shackles, and any below-the-hook devices. Forgetting to deduct rigging weight is a common cause of overload.
Structural Deductions
Certain attachments permanently reduce the available capacity:
- Stowed jib weight - must be deducted from main boom chart
- Auxiliary hoist components - if present, their weight is deducted
- Work platform attachments - derate to 50% for personnel lifting
These deductions are specified in the load chart footnotes and must always be applied.
Net capacity equals gross capacity minus all deductions (hook block, rigging, jib weight). The load must never exceed net capacity. Always calculate and verify deductions before every lift - ignoring rigging weight is a leading cause of overload incidents.