I'm not sure what the maximum height that mobile cranes can currently reach, but I believe that the mobile is a much quicker and less expensive solution. Typically there will be tow or three derricks employed in the that process, as a smaller derrick will be needed to lower the first derrick's piece to the ground, and if that smaller derrick cannot be disassembled into small enough pieces to be taken down in the hoist, then a third derrick, smaller still will be needed to lower the second derrick's pieces down to ground level.
I have never heard of a fourth derrick being required to take down the third one; I believe that the third one has always been able to be lowered back to ground in the hoist.
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