There are many options available to tree crews designing rigging systems. The more options there are to choose from, the lower the risk and the better the outcome will be. One of the risks in rigging operations is when using a system involving many components. If the components are not matched adequately to the system, many weak links can occur. Another risk is using advanced equipment and techniques without a thorough understanding of either.
Some people might consider the following techniques advanced, while others might see them as variations on methods presented earlier in this manual. Keep in mind the rigging principles of force, tree strength and equipment compatibility when you are considering these methods.
Keep in mind that any rigging system designed to move pieces horizontally, especially when set high in the tree, subjects the anchoring tree to higher bending moments. While a high anchor point is optimal for the travel distance, it also induces a bigger bending moment given the same load.
For larger, longer spans, or to decrease the bending moment on the anchor stem, consider a back stay, or even two back stays, to triangulate the anchor point.
Span rigging
Span rigging is a category of rigging methods in which the load travels away from the removal tree through the air across a span of distance. Examples are speed-line rigging – one line; and load transfer or basket rigging – two lines. These rigging systems allow the load to clear obstacles or move over distance to make brush hauling easier. Span rigging can be simple or complex to plan and install, but can greatly increase the efficiency of an operation, even if used only occasionally. Sometimes these systems are the only choice to efficiently remove trees that are a distance away from the chipper.
Why use span rigging?
• Move material easily and efficiently with gravity instead of crew energy
• Protect property and landscape with complete control over every cut piece
• A very useful system for removing conifer branches
Speed line
Speed-line rigging consists of a tensioned line angling from a high anchor point in the removal tree (or an adjacent tree). The line is either anchored near the ground to an adjacent tree or is held by a ground operator. Tree pieces are attached to the line and, when cut, they slide down the line away from the removal tree.
This method requires focus, good judgement and communication between the arborist aloft and the ground operator. Usually, minimal equipment is required, which makes speed lines quick and easy to set up. Despite its simple appearance, it is critical to understand rope angles and load forces when using a speed line.
Speed-line setup
Anchor-point selection
Anchor points in the tree need to be high enough for the speed line to work effectively. The wood pieces need to travel a long distance or clear obstacles, so the height at which the speed line is placed in the tree will be a critical factor. Make sure branches selected for anchors are strong and sound.
Anchor attachment
Several methods are available to attach the speed line to the anchor point ranging from tree wraps to rigging kits. A basic method is to use a suitable knot or hitch, such as a clove-hitch secured with two half hitches. Back up the anchor points when necessary to a lower branch or adjacent tree.
Equipment
For a simple speed-line setup, the arborist aloft girth hitches rope or webbed slings to the piece being cut. The rope or sling is attached to the speed-line rope by a carabiner. While this method is simple, the carabiners can create friction on the rope that might slow or even stall the descent if the rope has too much sag.
A pulley can be used in place of the carabiner to reduce friction as the piece descends. Select a pulley with cheek plates that do not bind on the rope. The pulley should have good contact with the rope and not swing or flip as it travels. A rigging plate can be attached to the pulley to handle multiple branches at the same time.
Rope
Select a rope with the right amount of elongation for the expected loads and angles. Consider the weight of the rope on the anchors over long spans.
Best Practices of Speed Lines
- Make sure the tree and anchor branches are strong enough for speed-line operations.
- Anchor the speed line high enough in the tree for the speed line to work effectively.
- Secure the rope to the tree using a suitable knot, such as a clove-hitch secured with two half hitches.
- Back up the anchor points, when necessary, to a lower branch or another anchor point.
- Select a pulley that will not bind or flip on the rope.
- Select a rope with the right amount of elongation for the expected loads and angles.
- Consider the weight of the rope on the anchors over long spans.
- Do not drop heavy pieces into the tensioned line. If you have to remove larger pieces, drop them first into a negative-rigging setup, then clip them onto the speed line.
- To estimate the speed of travel down the line, start with smaller pieces to adjust to the rope-angle speed.
- The speed line must be tensioned enough to carry the load over the length of the line, yet slack enough to minimize forces on the anchors and equipment.
- If significant tension is required to overcome the weight of a long run of line, or to gain clearance over a roof, load lighter pieces.
- Tension the line by hand, at first. If more leverage is need, use a mechanical-advantage system such as fiddle blocks. Do not overtighten or stress the rigging components.
- Remove mechanical-advantage devices before loading the speed line to prevent damaging them.
- For smaller pieces, apply tension before loading the piece on the line.
- Let the piece run smoothly down the line to help distribute the load forces. Avoid stopping the piece suddenly during its descent.
Speed-line loads
Weight
Smaller, lighter pieces are best for speed-line operations. Do not drop heavy pieces into the tensioned line. Shock loading the speed line can generate enough force to cause a failure in the system. Cut the piece into a negative-rigging setup, then clip it onto the speed line.
Speed
A steep line angle will create greater momentum as the piece travels down the line. It’s easy to underestimate the line angle and cause the piece to speed out of control. Start with smaller pieces to adapt to the line-angle speed.
Tensioning a speed line
The speed line must be tensioned enough to carry the load over the length of the line, yet slack enough to minimize forces on the anchors and equipment. However, if the line is too loose, the load will likely sag the line and stall.
So, how much tension should be applied? A hand-tightened line will work in most circumstances. Test the line with a small piece and observe how it travels down the line. Add or remove slack to get the right amount of tension for the load size.
If more leverage is need, use a mechanical-advantage system such as fiddle blocks – taking caution to not over-tighten or stress the rigging components. Remove mechanical-advantage devices before loading the speed line to prevent damaging them. For smaller pieces, apply tension before loading the piece on the line. For heavier pieces, load the line then slowly increase the tension and rope angle. This is easier to do with a lifting device such as a GRCS.
In speed-line operations, the direction of force can be pulling sideways against the tree. Force applied in this direction can turn the whole tree into a large lever. Do not overload the tree strength when using a high-tension speed line. Continually monitor all parts of the system for tension and alignment.
Reduce speed-line forces
• Do not shock load a speed line. Dumping heavy weights into a tensioned line can tear it off the rigging anchor with explosive force, causing other metallic rigging components to become airborne.
• Keep the rigging intact by keeping the loads small.
• Use an adjacent tree to guy or otherwise support the removal tree, if needed.
• Provide sufficient slack in the line to absorb the load impact without high anchor forces.
• Let the piece run down the line to help distribute the load forces.
• Control the descent speed of the piece with a tagline.
Speed-line tips
• Make sure all crew members stay out of the zone of travel.
• The load can be steered somewhat by moving the rope from one side to the other as the load travels down.
• For handheld anchors, watch the tip end – or lowest part of the piece – and release the line before the piece hits the ground. Otherwise, it could bounce into the crew member holding the line.
Vertical speed line
A vertical speed-line is similar to a regular speed-line in that the lowered pieces fall or travel along an anchored line. But, unlike a regular speed-line, a vertical speed-line drops pieces straight down along the trunk to avoid hitting targets just outside of the landing zone. A static line is run down the side of the tree and attached to the trunk using a sling and a shackle. The wood piece is connected directly to the line and is either lowered or allowed to free fall from the trunk as it is cut.
