11.5 Reading Mobile Crane Load Charts: Configurations, Range Diagrams & Chart Selection
Key Takeaways
- Load charts and deductions from capacity, including jib charts, range diagrams, and center of gravity, are an explicit Crane Knowledge topic on the NCCER Rigger written assessment; module 21301 Load Charts is the 35-hour source module.
- A hydraulic mobile crane publishes a separate chart for each support configuration: outriggers fully extended, outriggers at an intermediate setting, outriggers retracted, and on rubber — and using the wrong chart is a silent overload.
- On-rubber charts split further into stationary picks and pick-and-carry, which imposes creep travel speed, a stated boom position, and often an over-the-rear-only restriction.
- A range diagram is a scaled elevation drawing of boom length against radius and tip height; it answers whether the crane can physically reach and clear the pick, while the capacity chart answers whether it may.
- The operational notes are part of the chart: they define whether ratings are structural or stability based, whether rigging weight is included, wind limits, and the level-within-one-percent set-up condition.
11.5 Reading Mobile Crane Load Charts: Configurations, Range Diagrams & Chart Selection
The NCCER Rigger written assessment lists "define and describe crane configurations that affect load chart selection" and "load charts and deductions from capacity (jib charts, range diagram, center of gravity)" as Crane Knowledge topics. Module 21301 Load Charts is 35 hours — the largest single module in the Advanced Rigger curriculum.
Section 11.4 taught the deduction arithmetic. This section teaches the step that comes before the arithmetic: finding the right number to start from. A perfect deduction calculation performed against the wrong chart is still an overload.
Step 1: Select the Chart for the Configuration You Actually Have
A hydraulic mobile crane does not have "a load chart." It has a book of charts, one for each way the machine can be supported. The four you will see on virtually every hydraulic crane are:
| Configuration | What it means | Typical capacity effect |
|---|---|---|
| Outriggers fully extended | All outrigger beams out to the full-extension detent and set, tires clear of the ground | Highest capacities; the widest tipping axis |
| Outriggers intermediate / mid-extended | Beams pinned at a published partial-extension position | Reduced capacities, especially over the side |
| Outriggers fully retracted | Beams in, floats down | Substantially reduced capacities |
| On rubber (on tires) | Crane supported on its tires, outriggers not set | Lowest capacities, and further restricted by quadrant |
The crane's base and its configuration is what makes this matter: capacity comes from the distance between the center of rotation and the tipping axis, and the outrigger setting is what sets that distance. This is also why an outrigger that is not pinned at a published detent puts the crane on no valid chart at all — you cannot interpolate between outrigger positions.
On-rubber charts split again:
- Stationary on rubber — the crane picks without travelling.
- Pick and carry — the crane travels with the load. This is the most restricted mode: creep speed only, a stated boom length and angle, the load carried close to the ground with taglines, and very often an over-the-rear only restriction. Tire pressure is a rating condition, not a maintenance detail.
Other configuration variables that select the chart: counterweight configuration (a machine with partial counterweight uses the partial-counterweight chart), boom mode (main boom vs. erected extension), jib length and offset, and quadrant of operation (360 degrees vs. over-rear).
Step 2: Read the Capacity Table
A capacity table is indexed by boom length across the top and operating radius down the side. To use it:
- Determine the operating radius — measured horizontally from the center of rotation to the center of the vertical hoist line, under load (boom deflection increases radius).
- Determine the boom length required to reach that radius at the needed height.
- Read the intersection. That value is gross capacity, not payload.
- Never interpolate optimistically. If the actual radius falls between two rows, use the longer radius row. If the boom length falls between two columns, use the longer boom column. Both choices round toward the lower capacity, which is the only safe direction.
- Note whether the value is above or below the structural/stability dividing line (bold line, asterisk, or shading). Above the line the limit is structural strength; below it the limit is tipping. Section 9.1 covers the consequence of each.
Step 3: The Range Diagram
A range diagram is a scaled elevation drawing: an arc of boom lengths swept through boom angles, plotted against operating radius on the horizontal axis and tip height on the vertical axis.
The capacity chart tells you whether the crane may make the pick. The range diagram tells you whether it can — whether the boom is long enough to put the hook at the required radius and the required height, and whether the boom will clear the building, pipe rack, or existing structure on the way. Use it to:
- Find the boom length and boom angle needed for a given radius and hook height.
- Check available hook height after subtracting block, rigging, and load height from the tip height.
- Check boom clearance over an obstruction and around the load itself.
- Confirm the pick and set radii both fall inside the charted range.
Step 4: The Supporting Charts
| Chart | What it gives you |
|---|---|
| Jib / extension capacity chart | Capacity by jib length and offset angle, usually with a minimum main-boom-angle condition |
| Deduction chart | Manufacturer weights for the stowed jib, erected jib, auxiliary boom nose (rooster sheave), and hook blocks and balls |
| Parts of line / line pull chart | Maximum permissible single-line pull, and total permissible load by number of parts reeved. The reeved rope capacity can limit the lift below the chart value |
| Lifting area / working area diagram | Which quadrants are rated in the current configuration, including any zero-capacity zone over the front |
| Wire rope specification | Rope size, construction, and minimum breaking strength assumed by the chart |
The parts-of-line limit is a real constraint that candidates forget. If the chart says a crane can lift 60,000 lb at a radius, but only three parts of line are reeved and single-line pull is 15,000 lb, the rope system limits the lift to 45,000 lb gross regardless of what the capacity table says.
Step 5: Read the Operational Notes — They Are Binding
The notes page is part of the chart. Typical provisions that change the answer:
- Ratings basis. Whether values are limited by structural competence or by a stated percentage of tipping load — 85% on fully extended and set outriggers, 75% for a crawler on tracks without outriggers or a wheel-mounted crane on rubber.
- What is not included. Chart capacities almost always exclude the weight of the hook block, ball, slings, and any below-the-hook device. Those are the deductions from Section 11.4.
- Set-up condition. The crane must be level within 1% of grade on firm supporting surface; the chart is void otherwise.
- Boom deflection. Charted radii do not include deflection under load; the radius must be verified with the load suspended.
- Wind. Maximum permissible wind speed for the boom and jib configuration, and the requirement to account for the sail area of the load.
- Freely suspended loads only. No side loading, no dragging, no pulling a stuck load, no dynamic hoisting or lowering beyond the stated conditions.
Practical sequence for the rigger: configuration → correct chart → radius and boom length → gross capacity → subtract deductions → compare against the actual verified load weight → check parts of line → read the notes. Skip a step and the arithmetic will still come out clean while the crane goes over.
A crane is set up with its outrigger beams pinned midway between the published intermediate and fully extended positions. Which load chart applies?
A planned pick requires a 47-foot radius, but the capacity table lists rows at 45 feet and 50 feet. Which row must the rigger use?
What question does a range diagram answer that the capacity table does not?
A load chart shows 60,000 lb gross capacity at the planned radius. The crane is reeved with 3 parts of line and its maximum single-line pull is 15,000 lb. What limits this lift?