Tandem & Multi-Crane Lift Plans
Two cranes on one load is not two lifts. It is one operation with a load share that moves as the geometry changes. Planned properly by a CPCS A61 Appointed Person with 35 years of UK site experience.
The load does not stay where you put it
The instinct on a two-crane lift is to halve the weight and check each machine against its chart. That calculation is the starting point, and on its own it is not enough, because the split between the two cranes is not fixed. It moves during the lift.
If the two hoists run at even marginally different line speeds, the load tilts and weight transfers towards the lower hook. The same thing happens when the item is turned or upended, when the slings are not symmetric about the centre of gravity, or when one crane slews or travels slightly ahead of the other. A load that was evenly shared at the start of the lift can be significantly out of balance by the middle of it.
Rated capacity indicators do not protect you here. An RCI monitors its own crane. It has no idea the other machine exists, and it cannot see weight arriving from across the lift. By the time it reacts, the transfer has already happened.
That is why BS 7121-1 requires that where all the factors cannot be accurately evaluated, an appropriate down-rating is applied to all the cranes involved — commonly 20 per cent or more. It is also why the standard treats multiple-crane lifting as a complex lift, with the planning competence that category demands.
A written plan is not optional
L113, the Approved Code of Practice supporting LOLER 1998, is explicit that a written plan should exist where two or more items of lifting equipment are used simultaneously. There is no reading of the guidance under which a tandem lift is covered by a generic plan or a schedule of common lifts.
In practice this is rarely the argument. Principal contractors know a tandem lift when they see one and will ask for the plan. The problem is more often that the plan produced treats the operation as two single lifts happening near each other, which is precisely the misunderstanding that makes tandem lifts go wrong.
When a tandem lift is the right answer
- The load exceeds one crane’s derated capacity at the radius required
- A long member cannot be controlled on a single hook
- The load must be turned or upended during the lift
- Access prevents a single crane getting close enough for a one-hook pick
- Two smaller cranes are the only machines that will physically fit the site
The most common of these in UK construction is structural steel erection — long trusses, plate girders and pre-assembled frames that have to be lifted level and then rotated into position. Precast concrete panel erection and the upending of tanks, vessels and columns are the next most frequent.
Worth asking first: can one bigger crane do it? A tandem lift is always the more complex option, and where a single larger machine will physically fit and reach, that is usually the safer and cheaper answer. Part of planning a tandem lift is confirming it is genuinely necessary.
What the plan covers
- Load share calculation for each crane at each stage of the lift
- Derating applied to every machine involved
- Crane selection, standing positions and radii
- Ground bearing pressure, including compounding where cranes stand close
- Rigging arrangement, spreader beams and sling angles
- Synchronisation and the sequence of permitted movements
- Communication protocol and who holds control
- Exclusion zones and the abort position if the lift has to stop part-way
Side loading
A crane boom is designed to carry load in line. When the hoist rope is not vertical, a lateral force goes into the boom, and cranes have very little tolerance for it. On a tandem lift the ropes go out of plumb when the two machines drift apart or towards each other as the load moves — which they will, unless the plan says how they are kept together. Keeping the ropes vertical throughout is a planning requirement, not something to leave to operator judgement on the day.
Ground pressures compound
Two cranes standing close together do not each load the ground in isolation. The pressure bulbs beneath adjacent outriggers overlap, and the ground sees more than either machine imposes on its own. On made ground, over basements, or near service trenches this is the detail that gets missed, and it is why mat sizing on a tandem lift is worked from the combined case rather than crane by crane.
One person in control
The Appointed Person plans the operation. On the day, one lift supervisor holds control and gives every instruction, and the crane operators take direction from that person alone. This is not a formality. Split control on a tandem lift means two machines can receive conflicting instructions at the exact moment synchronisation matters most. The plan names who holds control, states the communication method — usually radios, because hand signals across two crane cabs are unreliable — and permits one motion at a time.
The abort position
The detail most often missing from tandem lift plans written by people who do not do them regularly. A lift halted with the load part-rotated is a different loading case from either the start or the finish, and it is exactly the point at which something has already gone wrong. The plan has to say where the load can be safely held, what each crane does, and how the operation is recovered — decided in advance, not improvised with a load in the air.
Tandem lift plans — common questions
What is a tandem lift?
A tandem lift is a lifting operation where a single load is shared between two cranes or lifting machines working together. Multi-crane lifts extend the same principle to three or more. It is used where one crane cannot take the load safely at the radius required, where the item is too long to control on a single hook, or where the load has to be turned or upended during the lift.
Does a tandem lift need a written lift plan?
Yes, without exception. The Approved Code of Practice supporting LOLER 1998 states that a written plan should exist where two or more items of lifting equipment are used simultaneously. BS 7121 also treats multiple-crane lifting as a complex lift, which requires planning by an Appointed Person with the competence to match. There is no version of a tandem lift that is covered by a generic plan.
How much do you derate the cranes for a tandem lift?
BS 7121-1 states that where all the factors cannot be accurately evaluated, an appropriate down-rating should be applied to all the cranes involved — commonly 20 per cent or more in practice. Many planners work to roughly a 20 per cent allowance for two cranes and larger allowances again for three or more, because the more machines involved the less predictable the share becomes. The figure is a planning judgement based on the specific lift, not a fixed number to be applied blindly.
Why does the load on each crane change during the lift?
Because the geometry changes. If the two hoists run at even slightly different speeds the load tilts, and weight transfers towards the lower hook. The same happens when the load is turned or upended, when the slings are not symmetric about the centre of gravity, or when one crane slews or travels marginally ahead of the other. Rated capacity indicators cannot prevent this — an RCI protects its own crane, it does not know the other machine exists.
Who is in charge of a tandem lift?
One person, and that has to be unambiguous before anything leaves the ground. The Appointed Person plans the operation; a single lift supervisor holds control on the day and gives every instruction. Crane operators take direction from that one person only. Split or shared control is the single most dangerous arrangement possible on a tandem lift, because the machines can be given conflicting instructions at the moment when synchronisation matters most.
What causes side loading on a tandem lift, and why does it matter?
Side loading happens when the hoist rope is not vertical, which puts a lateral force into a boom designed to carry load in line. On a tandem lift it usually arises from the two cranes drifting apart or towards each other as the load moves, or from one machine leading the other. Cranes have very little tolerance for side loading and it is a recognised cause of structural failure, so keeping the ropes plumb throughout is a planning requirement rather than an operator skill.
What do you need from us to plan a tandem lift?
The load: confirmed weight, dimensions, centre of gravity, and the lifting points available. The site: layout, crane standing positions, hardstanding and ground information, and anything overhead or adjacent. The operation: where the load starts, where it finishes, and whether it changes orientation on the way. And the cranes, if already selected. Where a site visit is warranted we will say so — most tandem lifts benefit from one.
How long does a tandem lift plan take, and what does it cost?
Typically 3 to 5 working days, because the load share calculations, crane positioning and rigging arrangement have to be worked through properly and a site visit is often justified. Tandem and multi-crane work is quoted individually rather than at the fixed rates we publish for single-machine plans, since the effort scales with the complexity of the operation. You will have a fixed-price quote within 4 working hours of sending the details.
Can two different cranes of different capacities be used?
Yes, and it is common. What matters is that each crane is working within its derated capacity for its own share of the load at its own radius, not that the two machines match. Mismatched hoist speeds are the practical problem rather than mismatched capacities — differing line speeds are a frequent cause of the load going out of level, so the plan has to address how the operators keep the movement synchronised.
Would a contract lift be better than planning it ourselves?
Often, yes, and it is worth saying so plainly. For a genuinely complex tandem lift a contract lift places the whole operation and its liability with the crane company. Where an independent plan makes more sense is when you already have the cranes arranged, when you want a second competent opinion on a plan a crane company has produced, or when the tandem lift is one part of a larger package such as a steel erection sequence.
Get a quote for a tandem lift plan
07803 8080933 fields, 30 seconds. We reply within 4 working hours.
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