
Understanding the Center of Gravity in Rigging
In rigging, the center of gravity is the point within a load where it balances evenly in all directions. Simply put, it’s where the weight of the load is concentrated. Identifying the center of gravity is crucial for safe rigging—lifting a load directly above this point ensures stability and control.
Determining the Center of Gravity for Common Loads
For uniform objects, like a single piece of pipe, finding the center of gravity is usually straightforward; it’s typically located at the center. However, even with such objects, it’s always smart to do a quick test lift. Raise the load a few inches to check its stability. If it begins to swing, set it down and adjust your rigging before trying again.
Center of Gravity for Complex Shapes
When it comes to objects with irregular shapes or uneven weight distribution, finding the center of gravity requires more precision. One approach is trial-and-error: estimate the center, rig the load, then perform a test lift, adjusting as needed. However, this can be time-consuming.
For a more efficient method, you can calculate the center of gravity using a simple formula. While it may sound complex, the process is straightforward. Below, we’ll walk you through the steps to quickly determine the center of gravity using basic tools—load links, a tape measure, and a calculator. This example will help you locate the east/west center of gravity; you can repeat the process for north/south.
Step-by-Step: Calculating the Center of Gravity
Step 1: Measure Each End of the Load
Begin by attaching a load link to each end of the load. Record the weight readings at both ends, which we’ll refer to as WL (left side weight) and WR (right side weight). Add these values together to determine the total weight (TW).
For example:
WL (Left End Weight) = 3,500 lbs
WR (Right End Weight) = 8,650 lbs
TW (Total Weight) = 12,150 lbs
Step 2: Calculate the Center of Gravity Ratio
Since the center of gravity lies closer to the heavier side, divide the heavier end weight by the total weight:
(WR / TW) = X
For our example:
8,650 / 12,150 = 0.71
This tells us the center of gravity is 0.71 times the distance between the two pick points, leaning toward the heavier end. If the load is heavier on the left, simply replace WR with WL in the formula.
Step 3: Measure the Distance Between Pick Points (SPAN)
Next, measure the distance between the two pick points, called the SPAN. In this example, it’s 126 inches. Multiply this distance by the result from Step 2:
(WR/TW) x SPAN
(8,650 / 12,150) x 126”
(0.71) x 126” = 89”
So, the center of gravity is 89 inches from the left end. With this information, you can rig the load accordingly. As always, perform a test lift to confirm balance.
Note: You can use feet, meters, or any other unit of measurement for this formula, as long as the units remain consistent throughout.
Complete Formulas
Use the appropriate formula based on which end is heavier:
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(WL / TW) x SPAN = CG
(WR / TW) x SPAN = CG
For more rigging insights, read our post on 5 Rules You Should Know About Rigging Safety.
If you have questions or need help calculating the center of gravity for more complex loads, reach out to your local LGH representative or call us at 800-878-7305. Our rental specialists can assist with finding the center of gravity for loads requiring both horizontal and 3D positioning.
Information and Illustration, copyright by Jerry Klinke, all rights reserved.
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