From the query, it is clear that you are not conversant with crane rigging. For God's sake, don't get carried away with the "I think..." answers in rigging. Tandem lift is a serious and dangerous operation. For that matter, every lifting operation needs to be considered as serious and dangerous. The history of crane failures says so. The consequences of a failure can be quite serious. However, by following the set procedures, every lift can be completed safely, allowing you to relax at the end.
Tandem Lift: A Critical Operation
A tandem lift (using multiple cranes) is a critical lift. It requires a lift plan.
Components of a Lift Plan
A competent rigger will draw a lift plan. A lift plan is required as part of any critical lift procedure and must provide the following:
• Type and de-rated capacity of cranes to assess SWL of the cranes (load chart) in the configuration
• Boom length
• Crane radius
• Weight and shape of the load, center of gravity, etc.
• Ground and site conditions
• Placement of the crane
• Swing and tail clearances
• Necessary communication to be used
• Explanation of hand signals
• Rigging hardware
• Rigging sketch
• Rated capacity of rigging components
• Sling angles
• Strain calculations
• Wind velocity
• Load moment indicator
• Others
Your cranes, as such, cannot lift the intended load, and no rigger/competent person will permit it.
Regards,
Kesava Pillai