Calculating the load angle for rigging

The crane rigging consists of an intricate system of slings, chains and belts lift properties using natural mechanical angles to distribute weights safely. The term “load angle” is used in these systems to describe the angle between any belt or chain and the surface of the charge that is held. For example, if a strap sling has been placed in each corner of a rectangular container, the load angle is the angle between the container lid and each corner sling, once it is suspended by the crane.


  1. Determine the desired weight of your load, consult the accompanying documents, sometimes known as the “cargo manifest”. This sum weight of the cargo container, a standardized number is usually available at the secretariat of the shipyard.
  2. Decide on the number of sling legs used to carry the load. Divide the weight full load among their number; for example, if the total load and weight of the container amounts to 1,200 lb (540 kg) load using sling divide by four, this weighing 300 lb (135 kg) distributed for each. This number is called the vertical load.
  3. Consult the manufacturer’s literature for each of your slings and determines the maximum rating, or “weight limit” of each sling. Divide the vertical load distributed on each leg sling for his highest rating. For example, with 300 lb. (135 kg) vertical load and a maximum rating of 600 lb (270 kg), the resulting division (300/600) corresponds to the number two. Using a calculator, press the “arcsine” (“arcsine”) button and “two” to find the angle of maximum load for your load and sling specific angle; in this case, this angle would be 30 degrees.

Tips & Warnings

Always check your numbers twice when calculating the maximum loading angle. As a rule, the angles of 30 degrees are very insecure, and generally are not used due to unnecessary tension exerted on the straps of the sling. Angles between 45 and 90 degrees are most common and safe for normal operation.