A lifting sling may have a rated capacity that appears suitable for a particular load. But the capacity of a multi-leg sling arrangement is not determined simply by adding the capacity of each leg. One of the most important factors is the sling angle.
Why Does Sling Angle Matter?
As sling legs move away from the vertical, the tension within each leg increases. This means that a sling arrangement at a relatively steep angle can experience lower leg tension than the same arrangement at a shallow angle. The angle mentioned here is the horizontal angle, and in the vertical case it is vice versa.
A Simple Example
Consider a load suspended using two sling legs. If the legs are relatively close to vertical, the vertical component of each sling’s tension carries much of the load. As the sling angle becomes more horizontal, each leg must generate greater tension to provide the same vertical lifting force.
Therefore:
Smaller sling angle = greater tension.
Why This Matters in Practice
Incorrect sling-angle assumptions can result in an apparently suitable lifting accessory being subjected to forces beyond its intended working load limit.
This is particularly important when lifting:
- Wide loads
- Long fabricated structures
- Machinery
- Steel structures
- Large components
Chain slings can be configured in different arrangements, including:
- Single leg
- Two-leg
- Three-leg
- Four-leg
The manufacturer’s rated capacity must be checked for the actual configuration.
Enhancing angled lifting with load monitoring.
For critical or complex angled lifting applications, incorporating a StraightPoint Radio Link Plus load monitoring system can provide an additional layer of control and visibility. By measuring the actual load being applied during the lift, the system helps operators verify that the load remains within the Working Load Limit (WLL) of the chain sling and associated lifting equipment. The wireless design also allows load data to be monitored remotely, helping the lifting team identify unexpected load increases or uneven loading before they develop into a safety concern. When used alongside correctly selected and configured Gunnebo Industries chain slings, load monitoring can support safer, more controlled lifting operations.
Centre of Gravity
Angle is not the only consideration. The load’s centre of gravity also affects how the load behaves during lifting. An off-centre load can result in unequal loading between sling legs. Therefore, the lifting arrangement should be designed around the actual geometry and centre of gravity of the load. The above video/sling angle write-up is based on symmetric conditions.
Do Not Simply Add Sling Capacities
This is a common mistake. If two sling legs are each individually rated for a particular load, it does not automatically mean the combined assembly can lift twice that amount under every configuration.
The angle and assembly configuration must be considered.
Use Manufacturer Tables
For critical lifting operations, capacity should be established using the manufacturer’s rated tables and applicable lifting standards. Operators should never rely solely on mental calculations or assumptions.
Manufacturer tables shall be considered only for perfect symmetric load; for any asymmetric load or a load with unknown Centre of Gravity, expert opinion matters.
What happens when a chain sling is overloaded?
Overloading a chain sling can have consequences that extend well beyond exceeding its rated capacity. Excessive loading can cause plastic deformation and permanent elongation of the chain, while generating residual stresses that may reduce the sling’s ability to safely withstand subsequent loads. Depending on the severity and duration of the overload, components such as chain links, hooks, and connecting hardware can become permanently damaged or weakened, even when the damage is not immediately visible. In extreme cases, continued or severe overloading can result in catastrophic failure of the sling and uncontrolled release of the load, potentially causing serious injury, equipment damage or fatalities. This is why the sling WLL, angle of loading, and condition of all components must be considered together, with appropriate load monitoring used where the application warrants additional control.
Conclusion
Sling angle is a fundamental factor in safe lifting. As sling legs become more horizontal, the tension in each leg increases. Therefore, selecting lifting hardware requires consideration of load weight, sling configuration, angle, centre of gravity, and Working Load Limit. Correct sling selection is not simply about choosing a sling that is “strong enough”; it is about ensuring that the complete lifting configuration is rated for the actual forces involved.