7/30/2019 Load and Rigging Calculation

1/3

Page 1 August 2011, Rev. 1

Example Load and Rigging Calculations

This example provides the basic steps for performing load and rigging calculations. Bobs

Rigging & Crane Handbook(latest edition) or equivalent handbook should be used as reference.

1. Determine the total weight of the load and rigging through:a. Documents, shipping labels, name plateb. Information from a qualified person (engineer, designer)c. Weigh the loadd. Calculate the load

2.

Determine the required working load limit (WLL) of the crane/hoist. The WLL of theweakest component must be sufficient to handle the load and associated rigging.

a. Determine the WLL of all hoist components andb. Verify that the WLL is sufficient

3. Determine the WLL for all rigging components.Example Problem:

A container filled with seawater is to be hoisted. Determine the following based on the diagram

below:

a. The weight of the container of seawaterb. The load on each of the sling legsc. The size and type of eye bolt to be used

7/30/2019 Load and Rigging Calculation

2/3

Page 2 August 2011, Rev. 1

Calculating the weight of the container:

Length (L) x Width (W) x Height (H) x Density = Weight.

The average density of seawater was determined to be 64 pounds per cubic foot. If uncertain,always verify density and other factors or calculations with a knowledgeable/competent person.

3 x 3 x 2 x 64 lbs/ft3

= 18 ft3x 64 lbs/ft

3= 1,152 lbs.

Calculating the load on each of the sling legs:

The vertical load for each sling = number of legs divided by the weight of the container

1,152 lbs divided by 3 legs* = Vertical load for each sling = 384 lbs

Calculating the tension in each sling leg:

1/sin 450

x vertical load = sling tension. 1.414 x 384 lbs = 543 lbsThe tension in each sling leg is 543 lbs. NOTE: calculate sling tension using 1/sin of angle oruse Load Sling Factor from the applicable table in Bobs Rigging & Crane Handbook.

* Use 3 legs for the load

calculation. One leg is

generally balancing the

load and cannot be usedin load calculations.

7/30/2019 Load and Rigging Calculation

3/3