Crane load charts accompany every crane and simply put, they give the capacities of the crane at a known radius for a known configuration.  These load charts will state what that given capacity means. For most heavy lift crane charts, it means the gross load to be lifted below the boom tip.  Therefore, when sizing a crane, one cannot just look at the heaviest module at a radius and compare it to the capacity of the crane at the matching radius.  Some deductions to look at that should accompany the weight of the modules are:

• Weight of the rigging
• Weight of the block
• Number of parts of line
• Weight of the parts of line
• Weight of any jib, ball, or any other item attached to the lifted load point
• Wind speed and wind sail

When sizing a crane, the weight of rigging could be estimated from previous jobs or it could be sized and calculated if enough is known about the module.  During a project, the actual rigging used and its weight needs to be summed up and deducted from the capacity listed in the load charts.

The weight of the block can be found in the crane load charts, but it should be requested from the crane rental house to know the exact size and weight of block that will be arriving on site.  This is especially required if you are planning on using a larger crane for smaller lifts. You may only need the minimum size block, but the rental house could send a much larger block which could affect the amount of net capacity you have to use.

The number of parts of line may be a deduction to the capacity of the crane.  If the total number of parts of line equipped on the crane have a capacity lower than the listed capacity of the crane, then the capacity of the number of lines governs.  To learn more about the number of parts of line, see our article here.

The weight of the lines is conservatively determined by taking the boom tip height multiplied by the number of parts of line and then multiplied by the weight per foot of line.  The crane manufacturer’s charts normally tell you in the general brochure what the weight per foot of the line is.

Another item to use as a deduction is the weight of anything attached to the boom tip.  This is usually a “rooster” sheave, a whip line, and ball.  The whip line with ball is usually a single part line to lift lighter items for quicker erection purposes.  The weight of the whip line is usually negligible since the ball will likely be pulled nearly to the “rooster” sheave during the heavy lift operations.  If lifting from the boom and a fixed jib is attached, then the fixed jib along with the rigging hanging from it must be deducted from the listed capacity of the boom.

Wind can also be a major deduction for lifting operations.  If lifting in higher winds, proper deductions must be made to the capacities of certain boom and jib combinations.  The crane manufacturers provide allowable wind speed operations based on specific configurations of the crane. Another area in which wind can govern is the “wind sail” on the load itself.  If you are lifting large panels with a large area, the wind can catch these and push the load out of plumb from the boom or jib tip. The wind speed that causes this may be lower than the operational wind speed provided by the manufacturer.  This “wind sail” effect needs to be calculated and considered during lifting operations.

We want to make sure you have a successful lift and that starts with proper planning and selecting the correct crane and setup for the job.  We can assist in this process by helping to create a lift plan, matting 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.