A load chart tells an operator whether a load can be lifted. The numbers on it are the crane's rated capacities: how much weight it can lift at a given radius or boom angle. But those numbers are not the weight of the load you can hang on the hook. Everything hanging below the boom tip has to be counted first.
Four terms to know
- Gross capacity: The crane's rated capacity, read from the load chart.
- Deductions: The weight of everything below the boom tip other than the load itself: the hook block or ball, rigging, slings, extra line, attachments, and any boom extension or jib.
- Net capacity: The gross capacity minus all the deductions. This is the most load you can lift in that set-up.
- Gross load: The load plus all the deductions. This is what the crane actually carries. It must not exceed the gross capacity.
Step 1: Find the gross capacity
- Know the set-up first: the chart section for how the crane is configured (for example, outriggers extended and the boom mode), and the main boom length.
- Find the column for your boom length.
- Go down to the row for your load radius, or your loaded boom angle. The number where they meet is the gross capacity, in pounds.
When you fall between chart values
Never estimate a number the chart doesn't give. Round toward the safe side:
- Between two radii: use the longer radius.
- Between two boom angles: use the lower boom angle.
- Between two boom lengths: use the lower capacity.
Check the line pull
If the gross capacity on the chart is more than the rope can pull with the parts of line you have reeved, the capacity is limited to the permissible line pull for those parts of line. A hook ball, for example, can only be used with a single part of line, so its limit is the single-line pull no matter how high the chart number is.
Step 2: Subtract the deductions
A crane's deductions are listed in their own section of its load chart. You don't subtract everything on the list, only what is on the crane right now. A crane might have a hook block on, no ball, and no boom extension, so only the hook block and the rigging count.
Net capacity = gross capacity (after any line-pull limit) minus the deductions that apply.
Step 3: Compare the load
The weight of the load itself must be less than the net capacity. If it isn't, change the set-up (a shorter radius, a different boom length, more parts of line) or use a bigger crane. Never lift a load and hope.
Always use the load chart for the exact crane and configuration you are operating. The layout of a chart differs between manufacturers and models.