There are two main ways to determine how many parts of rope or line you may need installed on your crane to make a lift properly and safely. 

First you need to decide whether you want to base your number of parts on the capacity of the crane in its configuration or based on the load you will be lifting.  These two approaches can lead to very different answers.

Let’s first discuss why the number of parts of line is important.  First and foremost you need to the proper number of lines to have the enough capacity to make the lift.  Secondly, on most cranes, the weight of the lines needs to be deducted from the capacity of the crane.  Therefore having an excess number of line parts reduces the amount of capacity you have.  The number of parts also affects the speed in which the crane block can be raised up and down.  The more parts of line installed, the slower the block will move up and down.  This can slow down a job.  Another issue to discuss is whether you have an even or odd number of parts of line.  In the past having an odd number parts of line has cause the crane block to tilt a bit versus having and even number of lines.

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The first approach to determining the number of lines required is to determine the maximum crane capacity that will be used on the crane you have configured.  You will then determine how many parts of line you need based on that capacity.  Each crane has a specified wire rope diameter that is to be used on it and therefore a specified rope capacity.  So if your crane capacity is 200,000 lbs. and your rope capacity is 20,000 lbs. you would divide 20,000 lbs. in to 200,000 lbs. to get 10 parts of line required. 

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The second approach to determining the number of lines required is to determine your maximum load below the boom or jib tip.  This maximum load includes the weight of the lift, the crane block, all rigging, and anything else that would be lifted by the crane rope.  So if you had 100,000 lbs. of load to lift, a crane block that weighed 20,000 lbs. and rigging that weighed 10,000 lbs. your maximum load would be 130,000 lbs.  Now if we stay with the previous example and use a line pull capacity of 20,000 lbs. then we would need 6.5 parts of line.  You would round this up to 7 or 8 parts of line depending on if you want even or odd parts of line. 

As you can see if you were to use the capacity of 200,000 lbs. or the maximum load of 130,000 lbs. you get a difference of two parts of line.  This adds a little bit of speed back to the crane and reduces the weight of the rope.  It is important to note that if you selected 7 or 8 parts of line, then your total capacity is less than the capacity of the crane listed on the manufacturer’s crane chart.  You need to note this on your lift plans so everyone involved knows that the crane is limited by the parts of line and not the crane chart. 

We want to make sure you have a successful lift and that starts with proper planning and selecting the correct crane for the job.  We can help in this process by helping to create a lift plan and help size the correct crane for the job.  Here at The Dothea Group, we will do our best to meet your schedule needs and we will provide efficient, engineered solutions to better your project, improve safety, and increase your bottom line. 

If you are interested in learning more about our engineering services, contact us today.  We can partner with you to ensure a successful bid or project.