Arbor Rigging: Knots, Hitches and "Do Nots"
Tree care professionals use rope in a variety of ways every day, sometimes in applications the rope manufacturer may never have even imagined or intended; and no matter how skilled, talented, experienced, or smart a climber or branch manager may be, if one is using ropes, one is using knots, hitches, or sadly on occasion “do nots” to attach the rope to various forms of woody debris. Almost everyone has a favorite knot or hitch, or perhaps just one that they’ve gotten into the habit of using and never let go of to see if something else is available or better. If the chosen hitch or knot is easy to form, strong, and secure, then no change may be needed, but having an idea of what might be available can also be useful, particularly in specific scenarios or situations where “old faithful” is just not up to the task at hand. As with all attempts to learn or incorporate new tools or techniques, users need to start out “low and slow,” and use their better judgment and experience before incorporating a new knot or hitch into their rigging system. After all, some person on the internet that expounds so knowledgeably may very well be an experienced thirty something climbing arborist that just tried this knot out today on a huge oak takedown and it rocks, or they may be a twelve year old who talks a good game and has read a couple of knot books.
All knots or hitches cause some strength loss in the rope they are tied in through the creation of bends in the fibers that make up the line. Thus, knots that minimize the strength loss of the rope, or put another way, retain as much of the rope strength as possible are the best choice, particularly in rigging operations where lines and knots are exposed to a great deal of dynamic forces. Unfortunately there is currently no ready reliable source for information on the relative merits in regard to strength for different rigging knots and hitches as it depends on rope, usage, climate and numerous other factors, but research done by organizations and individuals such as Dr. Brian Kane from the University of Massachusetts is beginning to fill this void, and hopefully will soon result in comparisons that tree crews can take advantage of when making knot choices.
Security, put quite basically, is how well or poorly the selected hitch or knot stays where it is placed/tied without slipping, moving, or letting go of the piece it is attached to. Obviously this factor is important in the use of all knots or hitches, but particularly so in rigging knots. In addition, certain species with slick bark or wood may stay secure with a standard hitch, but only if additional turns or “tweaks” are made in the knot.
Ease of use:
Ease of use is a factor in knot selection that can often be overlooked by the casual user. The reality is that a knot may be very safe/strong and secure, but so complex that it takes a great deal of time to tie and untie, leading to possible safety or efficiency issues. Typically if a knot or hitch is very complex, requires constant maintenance, and/or takes a great deal of time to tie/untie, mistakes are going to be made in its use; and in all likelihood there is probably a perfectly acceptable alternative knot or hitch without the same baggage available.
RUNNING BOWLINE WITH HALF-HITCHES OR MARLS
This knot is often used to terminate the rigging rope at a piece or branch, with the half-hitches or marls added for security or to hold the piece/branch a certain way once it is cut free. Rope strength research on rigging lines has shown that the Running Bowline actually has more strength without any marls or half-hitches; and the addition of them actually decreases strength, thus they should only be used in cases where there is a concern about the pieces’ orientation or that the branch might slip free from the Running Bowline. This hitch is simply a Bowline tied around the standing part of the line. It is created by passing the end of the line around the piece or branch, making a loop in the line, passing the end of the line around the standing part (capturing it), then feeding the tail up through the formed loop around the upper standing part of the line, and back down through the loop. The Running Bowline is intended to cinch up or choke against the branch or piece when loaded.
The Halter Hitch, a rigging knot observed being used by Wenda Li and Mark Cooke of Ontario is, like the Running Bowline, a choking hitch that cinches up to the branch or piece, but can be untied fairly easily. There is currently no data available on the strength loss in the rope created by the use of this hitch, but personal experience has shown it to be quite secure, and once learned and practiced, fairly easy to use. It is created by passing the end of the line around the branch, forming a loop, passing the working end over the standing part of the rope. This working end is then used to create a bight that passes under both parts of the line beneath the loop. The Halter Hitch is finished off by passing the tail over the both parts and through the created loop. Removing the tail from the loop and pulling it should easily release the hitch once the piece is on the ground.
The hitch that has traditionally been used to attach an eye sling is called the Timber Hitch. The eye sling can then be used for any number of rigging devices such as blocks, pulleys, or Port-a-wraps. A timber hitch is created by passing the eye sling around the trunk, capturing the eye with the tail of the sling, and then taking multiple twists or turns around the body or standing part of the sling back along the trunk. At least five turns should be taken; and more are always better. In addition the turns should be spread out along the whole length of the sling, covering at least half the diameter of the trunk. The Timber Hitch can tend to creep and move under load, so it should be checked and adjusted after every load to make sure all the turns are still there, and that they are spread out properly. This hitch should also always be loaded into the bight formed around the eye, so the eye pulls up against the bight not away from it; not doing so can whirl the turns right out of the hitch quite quickly typically with less than pleasing results.
COW HITCH WITH A BETTER HALF
This hitch is perhaps a better choice for attaching an eye sling than the Timber Hitch, requiring less attention and maintenance between loads, but does require a longer sling. The sling is once again passed around the tree, capturing the eye of the sling, but the tail of the sling goes all around the tree once more, passing back through the bight the eye is in. This action, in effect, creates a type of girth hitch around the tree. Finishing the hitch securely involves tying a half-hitch around the eye of the sling; with the tail of the sling exiting back toward the direction it entered the bight. This is the “better half” of the hitch. Any remaining sling can and should then be tucked beneath the sling on the trunk to get it out of the way of rigging operations, and perhaps provide some additional measure of security.
One of the most common ways to attach a line to branches or pieces of wood, particularly amongst traditionalists, is the Clove Hitch. It is certainly an effective hitch when tied correctly, although it does require more line to tie than some of the other hitches discussed here; and can have a tendency to “roll out,” meaning it must be “backed up” with two half hitches. In the Clove Hitch the working end of the rope is passed around the piece/branch, captures the standing part of the line, goes back around the branch, and comes out beneath the loop created by the first turn around the branch. When it’s done correctly, the line should exit on opposite sides of the hitch, with the piece of line on top running diagonally. Once again, it must be backed up with two half hitches tied around the standing part of the line.
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