With the increased focus on safety and the need for standardised testing and certification as provided by the NCCCO and other organisations, the field of rigging is finally coming under welcome study by folks outside the trade itself. With this study comes recognition that the verb ‘to rig’ is an easy term to describe but the noun ‘rigger’ is a different task altogether. Too often the world sees the ‘rigger’ only as the worker who hooks a load to a crane hook. There is a lot more to the trade than crane rigging. We must come to terms with what we mean by ‘to rig’ and ‘rigger’ before we construct a one-size-fits-all programme.
Rigging is simply the art of moving heavy objects. The difficulty comes in when one tries to describe the term ‘rigger.’ What is a rigger? I group riggers into four categories, depending on the sorts of skills required to move heavy objects safely and efficiently.
First are speciality riggers, who have full trade skills and speciality skills. These include millwrights, and riggers in offshore, nuclear, theatrical and rigging gear manufacturing environments, as well as tower, helicopter and floating derrick riggers.
Then there are industrial riggers, with full trade skills, working in shipyards, docks, and refineries; they perform heavy industry maintenance, railroad maintenance, in heavy construction, or with cranes.
Production riggers, such as occasional crane riggers, or commercial or residential construction riggers, or light industrial maintenance riggers, have only site-specific skills. They move pieces in a process that stays the same day after day
Finally there are the incidental riggers with only basic skills working in areas such as trucking or engineered production processes shifting and flipping units.
Fundamentally, the rigger is the same type of craftsperson as the electrician, steam fitter or plumber. The basic purpose of all of these trades is the safe, efficient and economical transfer of power from a source to a device that accomplishes work. The electrician takes electrical power generated at a power station, transfers it safely through various types of power lines and attaches it to a work-producing device at a job-site. The steam fitter, plumber and pipefitter do the same. Only the type of power, type of transmission lines and their work devices are different. They all operate in a specific way to keep their particular tiger in its cage. Riggers are no different. Only they exchange electrical, chemical or pressure energy for kinetic energy.
The rigging process
There are some essential skills and actions that need to be included in a formal definition of the rigging process. In my 40-plus years in the trade as a journeyman and instructor in various US Navy and commercial shipyards I have developed a description of the attributes of a rigger.
First there are the personal attributes that an assigned individual should possess to safely and efficiently perform any rigging task. Riggers need common sense; the ability to visually approximate where they and the piece are in the real world. This ability is similar to the military training term ‘situational awareness’; a kind of 3D thinking or mental peripheral vision. They need to be able to visually approximate, or see the big picture, in their mind.
Look around you. Where are you in relation to the real world? Can you visualise the load as it moves through your intended path?
Riggers need the ability to focus on the task at hand with all their mental facilities. If they are distracted, they lose a little of their situational awareness. Who or what can be lurking in that blind spot? The human body is a complex machine, and like all machines, things don’t always run at top efficiency. Pressure, time constraints, illness and personal issues can limit one’s focus on the job. The person tasked with a rigging move must be aware of these limitations and be prepared for them.
Rigging requires attention to detail: the ability to know what one is looking at and how that item behaves in relation to the rigging task. Riggers need to know what equipment they are using for the job, and its specifications and limitations as determined by a competent body. Smart workers do not know everything, but they do know where to find the information. They should keep a good riggers’ handbook with them at all times. They need the ability to recognise any detail that might impact their move.
Riggers also need social skills. They need the ability to communicate clearly through site-approved signalling methods. They need to work together safely and efficiently with everyone on the job. They need pride in their trade.
When a skilled rigger arrives at work, he will apply his abilities to a job. There are five definite steps in this rigging procedure. The first step is to identify the task, and scope out what they are being asked to do. They need to take into account the client’s needs, concerns and expectations, and discuss these items with the client to ensure complete understanding.
Step two is to identify the piece, and spend some time getting to know it. They need to be able to make it three-dimensional in their mind. They need to know the weight, of course, as given by documentation. Paper values should be verified by additional sources if possible. Shipping documents or third party suggestions are not as certain as engineering documents. There are standard methods for estimating weight of standard materials based on size. How does it balance? Will the piece shift, if its centre of gravity is not directly beneath the pick point? Will it flip, if the pick points are above the centre of gravity? When an object is lifted, its centre of gravity always moves plumb under the hook, and forces it to hang as low as possible.
Step three is to identify the space. Where does the piece need to go? Riggers should go there, have a look around, and picture the piece in the space. Does it look like it will fit? What and who is in the way? What path do I take? Is it safe? Is the path economical?
Step four is to identify the personnel and the gear. Who is involved with the move? Who will do the actual moving of the piece? Who needs to be present while it is moving? Who or what could enter the so-called ‘rigging field’ during the move?
The rig chosen will depend on how important control, grip and strength are in handling the load. A sling that runs from the hook to the top of the load, called a bridle, is best for control. The centre of gravity is low, keeping the load stable, but sling angles reduce the slings’ effective lifting capacity.
A sling passed through itself in a choker hold grabs in the middle and offers lots of grip. But choker grips cut the effective capacity of a sling by 50%. They require a constant strain on the load to keep it under control, and can crush delicate loads.
A sling passed underneath a load in a basket supports the load from the bottom and can even up-rate the lifting capacity of slings. But there are disadvantages; like chokers, they require constant strain to keep the load in position. The centre of gravity tends to be above the support points, risking flipping over. Two basket rigs inclined at an angle can pull the slings off position and risk dropping the load.
Dynamic loadings from a jerked load can change the effective weight of the load, and also affect the holding power of the sling configuration. Both chokers and cradles require the load to exert some force to keep the slings tight. If a crane operator suddenly dropped a double-choked horizontal pipe, the chokes would slacken and possibly shift toward the centre of the pipe, risking toppling the load.
Once riggers choose the rig, they need to select the necessary gear for the task. There are three types of gear: solid equipment, such as shackles that are not modified; slings and lines that can change shape to fit the task; and expedient gear, such as blocking, lashing and dollies. This gear should be approved by an engineer or a qualified rigger. Thought should also be given to who will put the gear away once the job is done to ensure it is carried out in a safe and proper manner.
The capacity of the gear also needs to take the rig into account. The
angles between multiple slings reduce the carrying capacity of slings. A 60° sling angle increases the load by 15%, while a 30° sling angle increases the load by 100%.
