Magic Glasses: Tandem Lifts with Hiabs
- Mar 16
- 5 min read
At first glance, using two Hiabs on the same load can look like a practical solution. Two cranes, two operators, and a load that appears manageable from both ends. When you put on the Magic Glasses, you start to notice something different. The operators cannot actually see how the load is being shared between the cranes.
Quick Scene-Setter
A large tank arrives on site.
It needs to be lifted off the transport trailer and placed into an excavated hole.
Because of the tank’s length and lifting points, two truck loader cranes are positioned - one at each end of the load.
Both cranes connect.
Both operators take the weight.
The tank lifts clear of the trailer and begins moving toward the excavation.
From the outside, the lift looks steady and controlled.
Tandem lifts with truck loader cranes usually occur because the load is long rather than because it is too heavy for one crane.
What Most People See
Most people see a straightforward lift.
Two cranes sharing the load.
Each crane appears to be lifting roughly half the weight.
The tank stays level.
Two operators working together.
If the tank weighs eight tonnes, the assumption is simple: each crane is lifting about four tonnes.
The lift appears balanced.
What the Magic Glasses Show You
Once you look closer, the lift is not actually balanced the way people assume.
In a tandem lift, the centre of gravity constantly shifts as the cranes move.
Small movements can cause the load to transfer between cranes.
This can happen when:
one crane slews slightly
one boom extends or retracts
one operator hoists faster than the other
the tank rotates as it clears the trailer
rigging angles change
the trucks move on their suspension.
As the tank is lowered toward the hole, the geometry of the lift changes again.
The load can suddenly move from one crane to the other.
One crane may rapidly take far more load than planned.
The Hidden Effect: Load Transfer Amplification
The cranes and the load form a connected mechanical system.
When one crane moves, it does not only move its side of the load. It changes the forces acting across the entire system.
If one crane lifts slightly higher:
the load rotates
the centre of gravity shifts
the opposite crane may suddenly carry more weight.
In crane engineering this behaviour is often referred to as load transfer amplification.
A small movement by one crane can produce a much larger change in load on the other crane.
The operators may not realise that the load is transferring.
The Rigging Angle Effect
Another factor that is often overlooked is the angle of the rigging.
Chains or slings rarely hang perfectly vertical in a tandem lift.
When rigging is angled, it produces both:
vertical lifting force
horizontal pulling force.
This horizontal force pulls the cranes toward the centre of the load.
If one crane moves slightly higher or lower, the sling angles change.
That change increases the force acting on the other crane.
In effect, one crane can begin imposing a load onto the other crane through the rigging system.
From the outside, the tank may still look level, but the forces within the lifting system can change rapidly.
The Truck and Ground Effect
Truck loader cranes introduce another subtle factor.
Unlike large crawler or mobile cranes, Hiabs are mounted on trucks with suspension and flexible chassis.
This means the crane is not sitting on a perfectly rigid base.
Small movements can occur when:
the truck suspension settles
the chassis twists slightly
an outrigger sinks into the ground
the load shifts during the lift.
Even a few millimetres of movement can change:
boom geometry
rigging angles
load share between cranes.
When one truck settles, or flexes, the other crane can suddenly take more weight.
The operators may not notice the movement, but the forces in the lift have already changed.
What the Crane Displays Actually Show
Most truck loader cranes display a percentage of capacity, not the actual load weight.
This means the operator cannot see:
the total weight of the tank
how much the other crane is carrying
how the load share is changing during the lift.
A percentage display only shows how close the crane is to its capacity limit.
It does not reveal how the load is being shared between cranes.
The most dangerous part of this lift is the invisible transfer of load between cranes.
What looks like two cranes lifting one tank is actually two independent cranes responding to a load that constantly shifts between them.
This is why tandem lifts are treated cautiously across the crane industry. International lifting guidance bodies treat multi-crane lifts as complex operations that require careful planning, defined load-sharing, and competent supervision.
Loader crane training guidance typically treats tandem lifts with truck loader cranes as exceptional tasks rather than routine lifting work.
The Controls That Matter
If two truck loader cranes are lifting the same load, the lift must be treated as a planned lifting operation.
Practical controls include:
Confirm the verified weight of the tank
Identify the centre of gravity
Calculate the expected load share between cranes
Confirm whether either crane could safely carry the load independently if load transfer occurs
Prepare a lift plan
Nominate a competent lift supervisor
Brief both operators and the lifting crew before the lift begins
Agree on a clear sequence of movements
Keep crane movements slow and coordinated
Maintain clear communication throughout the lift
Stop the lift immediately if the load transfer becomes unpredictable
Consider whether an alternative lifting method, such as changing from a Truck Loader Crane to a Mobile Crane, would reduce the risk. It likely does.
Magic Glasses Checklist - Tandem Hiab Lifts
Before connecting two Hiabs to the same load, check:
Why are two cranes required?
Is the lift required because of load length or weight?
What is the verified load weight?
Where is the centre of gravity?
What load share is expected on each crane?
Do the cranes only display the percentage of capacity?
Has a lift plan been prepared?
Who is supervising the lift?
Are both operators following the same lift sequence?
What is the stop point if the load begins transferring?
Two truck loader cranes lifting the same load can appear simple.
The challenge is that the most important force in the lift - how the load is shared between the cranes - is often invisible to the operators.
Small movements, sling angles, and even slight movement of the trucks themselves can cause large changes in load between cranes.
Magic Glasses thinking means recognising these hidden forces before the lift begins.
Once you understand what cannot be seen, you can plan the lift properly, control the movements, and maintain safe margins throughout the job.
Sometimes the most professional decision is recognising when the lifting method itself should be reconsidered.
Magic Glasses: The magic glasses come from the reality of - when I look at my books, I don't see a problem. But when my accountant looks at the books, it's a whole different story. He must have a special set of glasses.
As PCBU's, Officers and Workers, we have an obligation to learn what we are up to and the risks. Our actions and the standards we accept also affect those around us. This magic glasses post is made to help others see what we see.
