The number in a crane's name — "a 60-tonne crane", "a 100-tonner" — is its capacity in the most favourable position: boom retracted, load almost next to the superstructure, outriggers fully out and full counterweight fitted. Real jobs rarely look like that. What the crane can lift in your conditions is shown only by its load chart — the key document when choosing a crane.
Rows and columns
For a mobile crane with a telescopic boom the chart is usually laid out like this:
- Rows are radius, in metres: the horizontal distance from the slewing axis to the load's centre of gravity — not to the edge of the carrier or the wheels.
- Columns are main boom length, in metres.
- Cells are the permitted load, in tonnes, for that combination.
Above the chart the conditions are always stated: how much counterweight is fitted, how the outriggers are set (fully extended, partially extended, on wheels) and the working area — over the rear, over the outriggers or a full 360°. Each combination has its own chart; a crane manual may contain dozens of them.
A simplified example
Below is a simplified chart for a notional 60 t class crane (outriggers fully extended, full counterweight, 360°). The figures are illustrative, but the proportions are typical of real cranes.
| Radius, m | Boom 12 m | 20 m | 28 m | 36 m |
|---|---|---|---|---|
| 3 | 60 | 42 | — | — |
| 5 | 45 | 38 | 30 | — |
| 8 | 30 | 27 | 24 | 18 |
| 12 | 18 | 17.5 | 16 | 13 |
| 16 | — | 11 | 10.5 | 9.5 |
| 20 | — | — | 7.5 | 7 |
| 24 | — | — | 5.5 | 5.2 |
The key point: capacity falls very quickly as radius grows. Sixty tonnes is available only at three metres; at sixteen about ten remain. A dash means the combination is geometrically impossible (a short boom cannot reach) or not permitted.
Step by step
- Work out the total load. Add the hook block, slings, spreader beams and shackles to the weight of the load itself. The crane manual lists the hook block weight separately; on large cranes it runs to hundreds of kilograms or more.
- Find the radius from the site plan — from where the crane will stand to the centre of the load at the farthest point it must reach. Check both the pick point and the set-down point.
- Find the boom length you need from the height: the load and rigging must clear obstacles with a margin.
- Find the cell. If there is no exact value, take the worse one. Round the radius up to the next row, and take the boom column that gives the lower load. Never interpolate in your favour.
- Compare. The total load must not exceed the value in the cell.
A worked example
An air-handling unit weighing 9 t has to go onto a roof. The hook block weighs 0.5 t, slings and spreader 0.2 t — 9.7 t in total. The site plan gives a 14 m radius; the height needs a boom of about 26 m.
There is no 14 m row, so take the next one, 16 m. There is no 26 m column, so take 28 m. The cell shows 10.5 t. That is more than 9.7 t, so the lift works, but with less than a tonne to spare. If the unit has to be set at 20 m, only 7.5 t is allowed — you need a bigger crane or a different crane position.
Conditions that change everything
- Outriggers. The "fully extended" chart does not apply if the outriggers are only half out because of limited space. Partial extension has its own chart with noticeably lower figures.
- Counterweight. Large cranes have their counterweight delivered on separate trucks. If only part of it is on site, work to the chart for that counterweight.
- Working area. Over the rear outriggers a crane is usually more stable than over the side. If the chart says "over rear only", the load must not be slewed over the side.
- Ground. Charts assume level, sufficiently firm ground. Soft soil, slopes or the edge of an excavation call for a separate assessment and outrigger mats.
- Wind. Each crane has a maximum permitted wind speed, and for loads with a large surface area (panels, blades) the limits are lower still.
Why "just a little over" is not allowed
The chart already includes a margin against tipping and against overloading the steel structure, set by the standard the crane is certified to. That margin exists for dynamics: load sway, braking, gusts. Eat into it and you lose protection exactly when you need it. The crane's load moment limiter is a safety net, not a planning tool.
What to check in the catalog
Kranovshik model pages list maximum capacity, radius, hook height and boom length. That is enough for a first shortlist — it quickly rules out cranes that cannot possibly do the job. The final decision is made only from the load chart of the specific crane in the required configuration, supplied by the manufacturer or the crane owner.