Understanding the effect of angles on sling capacities is a critical part of safe rigging.
You should know that using slings at an angle can quickly become deadly if the angle is not considered prior to selecting which sling to use. This is because the tension on each leg of a sling increases as the angle of the sling from horizontal decreases. Given that, the most desirable angle of lift is one that approaches 90 degrees. The inverse relationship between the angle of lift and sling tension also dictates that lifts with angles of less than 30 degrees from horizontal are not recommended.
Luckily, if you can measure the angle of the sling or the length and height of the sling as rigged, you can determine the properly rated sling for your lift. This is referred to as the Load Angle Factor (LAF) or Tension Factor (TF).
To calculate increased tension, you can start by asking yourself the most basic question:
What capacity sling do I need?
To do this:
- First, determine the weight the sling will be lifting.
- Then, calculate the TF. Using the angle from the horizontal, read across the angle chart to the corresponding TF column.
- Divide sling length* (L) by measured height* (H).
- Then calculate Lifting Weight (LW) x TF = Minimum Sling Rating, for a single leg, for the type of hitch that will be used.
*Measured from the horizontal plane bearing point to the bearing point on the hoisting hook.
To calculate capacity reduction, ask yourself:
What would be the rating of each sling rigged at this angle?
To do this:
- Firstly, divide the sling height* (H) by the sling length* (L) to calculate the Reduction Factor (RF).
- Secondly, using the angle from horizontal, read across the Angle Chart to the corresponding number in the Reduction Factor column.
- Calculate the Reduction Factor (RF) by dividing the measured height* (H) by the sling length* (L).
- Reduction Factor (RF) x the sling’s rated capacity for the type of hitch that will be used = the sling’s reduced rating.
*Measured from a common horizontal plane to the hoisting hook.
Download the Rigging Section of the LGH catalog for more information about rigging equipment types and specifications. For further support, click to chat with a live rental support specialist or call 800-878-7305 now.