Until just over four years ago, I barely knew what a knuckleboom crane was – and I may not be alone! Now it seems they are all I think about. There has been a dramatic rise in popular use of knuckleboom cranes for tree work since TCI EXPO 2015 in Pittsburgh, Pennsylvania, where we got our first taste of a grapple saw on a knuckleboom crane.
At that show, only one fully operational machine was on display, with a static display of another grapple saw and a grapple saw hanging from a knuckleboom crane that was not yet outfitted with the hydraulics to the boom tip to operate it. If you were at the 2019 show (again in Pittsburgh), I don’t have to tell you what an increase there was in operational grapple saws displayed on knuckleboom cranes.
This technology is coming on the scene quickly – about as fast as the trucks can be set up with a crane on them – and many times to new owners without any, or very little, crane-operating experience of any kind. This article will discuss the setup and operation of knuckleboom cranes themselves. A subsequent article will address the best practices for knuckleboom cranes with grapple saws. I hope this article offers some useful information to new operators/owners, as well as brings up something new, or at least serves as a refresher or reminder, for veteran operators.
Even after I made my own decision to buy a knuckleboom crane with a grapple saw, I had no real idea what I was getting into or how to operate it. I had logged thousands of hours operating a truck-mounted, knuckleboom log loader and felt pretty confident in my abilities. I guess so much so that when I picked up my brand-new crane, I received about an hour’s worth of familiarization with it and away I went. Fortunately, apart from being painfully slow, I had no lasting or job-stopping mistakes as a result of my lack of training.
Now every new owner/operator receives at least a full day or two of training from their dealer before being left on their own. Having knowledge and proficiency in traditional tree work, such as climbing, aerial-lift operation, chain-saw use, and rigging, without a crane is invaluable. It makes for a well-rounded operator who can identify hazards, create a work plan, prevent machine damage, understand the way trees and their branches act and react when cut off and be more efficient when working with the crew and disposal equipment.
So, let’s talk about best practices for knuckleboom cranes in tree care. Articulating-boom cranes commonly referred to as knuckleboom cranes or K-booms, are made to do the same thing as any other crane – lift and move things from one place to another by means of boom reach and swing. However, K-boom cranes are quite different from a “stick”/cable crane.
K-booms have a very useful if not impressive load chart at horizontal and even negative boom angles. And K-booms were designed for use in environments with very limited space such as is common in Europe, so they are intended to be versatile and flexible both in set-up requirements and operations capabilities.
It should be noted that removing trees with a knuckleboom crane exposes the crane to hazards such as tree branches and logs. There are numerous parts and components that can be damaged due to an oversight or a “non. sight.” I will attempt to list and then address items/topics in a manner that seems to be the order of operations, meaning first things to happen first, although, as we know in tree work, things sometimes get mixed up just because of the nature of the job site or tree.
Please remember, although this article may not elaborate on some of the best practices (and I will miss some things), we are each responsible to work and operate in a safe manner to protect those around us, property and ourselves. Our goal is to go home safe every day – at least, I think it should be. Adding a piece of equipment with remote control that reaches up to 120 feet vertical or 110 feet horizontal expands the danger/work zone by more than you might think.
Each site is unique and may require more considerations than are listed here.
Topics we’ll discuss include:
• Trained/certified operator
• Personal protective equipment
• Crane properly maintained & inspected
• Pre-job briefing
• Driving/parking surface stable and can support the truck
• Footing under stabilizer locations can support pressures to be exerted
• Slopes (if any) can be mitigated
• Obstacles – physical barriers, wires, roadways, bystanders
• Drop/fall zone underneath the tree
• Landing zone and pathway to landing zone
• Proper setup of crane
• Operation of crane
• Limitations of manual extensions
• Lifts/picks with slings
Trained/certified operator
Well-trained, skilled operators will be the most productive overall. Production takes into account getting the work done expediently, balanced with less time in the repair shop. Any operator should recognize his or her true skill level and operate within it. It is alright to acknowledge personal limitations; in fact, it is better to do so rather than have an incident. Proper training highlights the need for patience and discipline, which are equally important when operating a knuckleboom crane. The phrase “slow is smooth and smooth is fast” could not be more accurate in describing the best way to operate a knuckleboom crane.
The time to learn and elevate one’s skill level is when there is a trainer present, or at least in a situation where the margin for error is wide enough to accommodate a mistake or misjudged move. Crane-operator certification – even for tree work – is required in some regions and is definitely worth achieving for every operator. It can help to increase confidence in ability and knowledge, having tested to a national level standard.
Personal protective equipment
Personal protective equipment, or PPE, is a must, no matter how far removed from the action one thinks they are. Obviously, hard hat, eye and ear protection, and whatever else is needed for the environment or task, such as reflective safety apparel or chain-saw cut protection, is required.
Crane properly maintained and inspected
Having the crane properly maintained and inspected is part of knowing your equipment; understand it and how it works. Another article could be written on maintenance and inspections, as there is so much to know. Inspections should be completed daily; more in-depth inspections also should happen periodically, such as weekly, monthly, and, of course, the annual inspection and certification. The annual inspection is a time for specially trained persons to inspect the crane thoroughly, looking closely at specific places where problems have occurred in other cranes of the same kind. An outside perspective is invaluable for the annual inspection.
Maintenance goes hand in hand with inspections. Activities such as greasing and lubricating are a perfect opportunity to look the equipment over for anything missing or out of place. A good operator also will be continuously watching the equipment during operation for anything out of place or something like a hydraulic hose failure or damage to hose tracks and trays or reels.
Pre-job briefing
The pre-job briefing should include everybody on the crew. It should highlight the safety aspects, as well as how it is intended that the work be completed and how each member plays a part and will interact with other crew members as the work is happening. It might be worth mentioning knuckleboom-crane-specific information when working with a crew or crew member with limited experience with knuckleboom cranes.
Driving/parking surface stable and can support the truck
We need to be certain the surfaces we drive the truck over and onto will be able to support the weight of the truck, as well as any increased loads on wheels/tires during operation of the crane as the crane takes up loads. In addition, the tires are responsible for maintaining the lateral position of the truck even while the crane is operating. It is not desirable to park the truck with tires on bare ice or any other slippery surface. Use sand or some other sort of gripping material, such as a piece of expanded metal mesh. Salt is not effective in gaining traction, because it melts the ice and creates water, which increases the slickness of the ice. Wheel chocks should always be used as a safety measure against brakes out of adjustment or a sliding wheel, but they will not be effective if the tires and wheel chocks are on ice.
Footing under stabilizer locations can support pressures to be exerted
The footing for the planned stabilizer location must be able to support the pressures that will be exerted and be close enough to level that the stabilizer foot can self-adjust to match. Even a well-constructed street may not be suitable for placing a bare stabilizer foot without padding. Sidewalks and driveways can be a problem because we generally have to compensate the owner if we damage them. Staying off of corners and edges with the pressure points (or building up on either side and somewhat bridging the corner or edge) goes a long way toward avoiding damage. (Photo 3)
It is also imperative that the stabilizer footing is not on a ground surface that could collapse into a hole or basement, and is on sufficiently firm ground (fresh fill and deep mud will push down or out under the loaded stabilizer). For holes and basement foundations, the stabilizers need to be set back 1 foot for every foot of depth of the hole or foundation in compacted stable soil, or 1.5 feet for every foot of depth in sandy soil.
Slopes (if any) can be mitigated
If the setup is on a slope, the determination of if and how to mitigate that slope needs to be addressed. Each manufacturer will have a guideline of degrees out of level that are allowable. Consult your operator’s manual for this. K-booms need to have their wheels on the ground, so the foundation for the truck needs to be built up in the low areas where the tires will be. Some rigs will be able to lift the wheels off the ground so blocking/cribbing can be set up, and others need to drive onto the cribbing. Obviously, the blocking and cribbing need to be of sufficient strength to resist crushing, as well as have sufficient grip to prevent movement while positioning and working. (Photo 4)
Why should slopes be mitigated? There are a number of good reasons, mostly relating to preventing long-term damage to the crane:
• Repeated overloading of the swing/ rotation mechanisms will lead to damage and possible failure of the mechanical parts, i.e., broken gears will allow the crane to swing freely with no control.
• The boom sections will twist against each other within the slide pads and alignment pads. This happens repeatedly as the boom is swung around from one side of the angle to the other when setup out of level.
• In extreme situations, excessive side loading will occur, placing stress on the boom in ways that it was not designed to withstand.
• If the crane is set up out of level, when the jib is angled downward, the side profile angle will be the same as the slope when the boom rotation is at 90 degrees to the slope angle. This not only side loads the jib and affects the alignment slides, but also transfers a twisting force into the main outer- boom extensions and will affect the alignment slides if the boom is extended or retracted.
One more thing that can happen when the crane or stabilizers are set up on a slope without mitigation is that, when the crane boom takes up a load, which is then transferred down the booms through the inner boom, column, base, three-point bridge and chassis to the stabilizers, the down pressure shifts between stabilizers, causing lateral movement of the padding or even the entire truck. It is normal to experience stabilizer lift on the opposite side of the load, but a good operator will anticipate the occurrence and plan accordingly.
Obstacles: physical barriers, wires, roadways, bystanders
Obstacles come in many forms. Typically, there are other trees, buildings, wires, and roadways to avoid and even bystanders. I don’t want to get into more depth at this time, but we all know that contact of any kind with energized lines is not acceptable. Contacting the primary conductor (7,000 volts in my area) with the boom or anything attached to it or drawing an arc (yes, it can arc) ends the tree work for the day or longer. Make it a practice to stay clear of the wires using the OSHA and ANSI standards as a minimum. Remember also that an event could happen a block away or farther, which could cause wires to move or fall down. These kinds of events are rare, but coupled with inappropriate approach distances, they could be disastrous.
Drop/fall zone underneath tree
Part of the site inspection and possibly even the pre-job briefing should include assessing the “drop” or “fall” zone underneath the tree. This is the area underneath the tree that would be affected should a dead branch fall off or another branch be broken and fall. As the tree sections are secured to the crane and then swung to the landing zone, the fall zone moves with the load and is not only directly under the load but also for some distance laterally in all directions. A load can come loose and be deflected so it does not fall straight down, so this must be accounted for when determining safe zones for personnel or bystanders.
Landing zone and pathway to landing zone
The landing zone is, of course, where the tree sections will be placed for further processing or staging. The size of the landing zone, as well as the pathway to it, must be considered in the job plan. Whoever is determining the branch-section size to be removed for each pick must take into account the crane capacity and physical space limitations in all three areas – landing zone, pathway to landing zone and the original position in the tree.
Proper setup of crane
Now that all the preliminary assessments and decisions are in place, the crane can be set up for operation. Any cribbing for tires is in place and secure and the truck is in the desired location, allowing for the boom to be unfolded and placed into the operational configuration. Wheel chocks are in place. One benefit of K-booms is that they are engineered to be used with many different stabilizer extension possibilities. Some cranes are even set up so the crane’s computer monitors stabilizer extension and actively adjusts the crane capacity accordingly.
Without that system, we must be vigilant when operating without all stabilizers at full extension to be sure an extended boom or load is not swung to that quadrant. It is best practice to have all stabilizers out completely, but allowable to short-span the non-load side.
If there is room, extend all stabilizers completely. Short-spanning the load side should be avoided except when there is a computer-controlled adjustment or a provided load chart to reference. Stabilizer footings should be at least somewhat flat; with too much angle, the pivoting foot on the stabilizer leg will be damaged and there is an increased likelihood of “pad walk.”
Stabilizer feet should be put down with enough pressure to slightly unload the truck suspension. When the tires rise slightly but are still squished out where they make contact with the ground, that is about right. Generally, setting the lower-side stabilizers first is helpful when on a side slope.
Operation of crane
Although there are many aspects of crane operation, what seems to be the most important issue is smooth operation. This means starting and stopping movements gently so that neither the boom nor load makes quick jerky movements that put stress on the crane. Smooth makes for easier work and greater longevity of the equipment, as well as increased trust from others involved in the operations.
Lifts/picks with slings
Swinging or moving the boom or loads over people is to be avoided. No one expects a failure of a load sling, the tree branch, or a boom, but it does happen. If we can remove the risk to personnel, then we can reduce the risks and hazards on the job.
• Do not use the swing mechanism to induce force to a load that is not free-hanging, as this causes side loading as well as wear to the swing mechanisms.
• Dragging loads on the ground by pulling in with the extension cylinders is not allowed. This can cause gross overloading of all components, especially those not engineered and designed to withstand those types of applied forces. If a load is too heavy to lift where it sits, it should be cut smaller or moved closer by another means, such as rolling.
• Reducing the load radius after a pick decreases the load as a percentage of capacity and also reduces the stress on the crane and chassis.
Picks and lifts using slings and traditional rigging should be planned the same as when using a stick crane. Both the Green Log Weight Chart and the load chart of the crane must be used when planning a lift or pick. One thing to remember is that, for persons rigging and de-rigging, instead of a large steel ball suspended from a cable, the hook is connected directly to a boom. Keeping clear of the space between the boom and something that does not move needs to be standard practice. In addition, the operator must avoid putting a person in a compromising position or situation where that person is unable to react or move (back turned and busy or a climber in the tree).
Limitations of manual extensions
When using a manual pull-out extension, do not exceed the load-rating label on the manual extension. The extended manual extension is not able to support the same loads as the hydraulic extension into which it is inserted. It is important to remember that the larger cranes have manual extensions rated for larger loads than smaller cranes. A 110-meter-ton (a rated measurement of torque) crane has a fly jib almost as large as the main boom of a 33-meter-ton crane, so the manual extension is built accordingly.
Conclusion
There are many aspects to operating a knuckleboom crane. Approaching the work step by step and taking the time to train, maintain, and plan, followed by executing the work, will pay off. A very special thank you to Alex Gulledge and Rick Yoos for their help and contributions to this article. In the next article, we’ll look at best practices for knuckleboom cranes with grapple saws.
Ben Heller is the owner and chief operations officer with Hiawatha Tree Services, a 10-year TCIA member company based in Minneapolis, Minnesota.
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