Tandem lifting is what you do when a load is too heavy, too long or too awkward for one hook. It doubles the capacity available and roughly quadruples the planning. Below is how a 220-tonne process vessel gets from a transport frame to its foundation.
Step 1 — Load study
Certified weight, centre of gravity, lifting-lug positions and permissible tailing loads come first. A centre of gravity 200 mm off assumption changes the share between the two cranes and can overload one hook while the other reads comfortable.
Step 2 — Crane pairing and derating
Tandem configurations are derated — typically to 75% of combined chart capacity — to absorb dynamic effects and load-sharing error. We pair machines with compatible boom geometry and hoist speeds so the load stays level through the lift.
Step 3 — Rigging design
- Spreader beams and slings selected to lug geometry with documented certification
- Tailing crane sized for the peak load during upending
- Rigging weight fed back into the crane load calculation
- Tag lines planned for wind and rotation control
Step 4 — Ground and access
Both crawler pads are surveyed, proof-rolled where required and matted to the calculated bearing pressure. Travel paths under load are levelled and marked; a 220-tonne pick is not the moment to discover a buried service trench.
Step 5 — Rehearsal, then execution
The crew walks the sequence with a single lift supervisor, one radio channel and agreed hold points. Trial lift, hold, verify hook loads, then proceed. On the campaign that produced this article, the vessel was set and released ahead of the planned window.
A tandem lift is decided in the office. On site you are only confirming the paperwork was right.