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1. The parts of the chart
A Jekko or Maeda load chart is a grid. Down the left side are working radii, the horizontal distance from the center of rotation to the hook. Across the top are boom lengths, usually one column per telescoping stage. Each cell is the rated capacity in pounds for that radius at that boom length. Blank cells mean the combination is not rated: either the boom cannot physically reach that radius at that length, or the manufacturer has not certified it.
Above the grid you will find the conditions the table applies to: the machine model and revision, the outrigger configuration or stability level, the attachment (main boom, jib, searcher hook), the number of rope falls, and the counterweight state where that applies. Every one of those has to match your setup or you are reading the wrong table.
2. Radius first, always
Radius is measured from the center of rotation, not the edge of the tracks or the outrigger pad. Use the reference point shown in the exact machine documentation. Measuring from the front of the machine understates the radius and can turn an apparently acceptable selection into an unrated lift.
Read the radius at the least favorable point in the lift, not just the start. A load picked close to the crane and set farther away must be checked through that whole path. Include the swing and any additional reach needed to clear an obstruction.
3. Boom length and the column trap
The boom-length column matters because a different boom length at the same radius means a different angle and structural condition. Read the chart at the actual boom setup. For positions between printed columns, follow the manufacturer instructions for that chart. Do not assume an adjacent cell authorizes a blank or unrated configuration.
4. Outriggers, attachments, and falls
Outrigger configuration
On Jekko SPX machines, the stability level determines the applicable table. Other manufacturers label setup configurations differently, including outrigger position and operation on tires or outriggers. There is no universal percentage that converts one table into another: select the chart matching the exact model and setup. The J-zone explainer describes the Jekko approach.J-zone explainer
Jib and attachments
A jib has its own chart indexed by jib extension and luffing angle. It is not the main-boom chart with a deduction. The same is true of a searcher hook or a glass manipulator, which carry their own weight that comes off the rated figure.
Parts of line
The permitted line pull and reeving are additional limits. Check the manufacturer instructions for the winch, hook block, and number of parts of line actually fitted. A larger chart cell does not override a lower limit elsewhere in the lifting system, and adding rope parts does not by itself authorize a higher load.
5. What to subtract
- Hook block or overhaul ball, unless the chart footnote says it is included
- Slings, shackles, spreader bars, and lifting beams
- Glass manipulator or vacuum lifter, including its battery
- Jib weight when a jib chart does not already account for it
- Anything else hanging from the boom tip
Net capacity is the chart value after all deductions required by the manufacturer. Compare the load with the remaining allowance, not with the headline rating. Record the verified weights of the hook block, rigging, and attachments so none is overlooked or counted twice.
6. A chart-reading workflow
Work from the technical data sheet for the exact machine, revision, boom, outrigger setup, and attachment. The following sequence describes the checks without supplying an unverified rated-load example.
- Measure the governing working radius and apply the chart instructions for a position between rows.
- Match the actual boom extension to the permitted chart configuration.
- Confirm that the selected row and column contain a rated cell. A blank cell is not a usable capacity.
- Check reeving and every other applicable equipment limit against that cell.
- Apply the manufacturer deductions using verified hook, rigging, and attachment weights.
- Compare the load with the resulting allowance and verify the complete lift path, setup, and site conditions before proceeding.
Changing the outrigger configuration can change or remove the rated cell. The same crane and radius do not guarantee the same allowable load on a different footprint.