Basic Highline System with Pulleys, Rope and Pulley Systems for High Angle Technical Rescue
Highline operations are one of the most dangerous and most difficult vertical rescues. Highline rescues invoke the use of advanced rigging skills, performed by advanced technicians. Under no circumstances should a highline be attempted solely on the instruction of this book. Anyone interested in performing a highline must have intermediate skills, and seek advanced training through an accredited school of rope rescue. This section of this chapter gives only a general overview of this extremely complex subject of highlines.
99% of the time, most high-angle rescues can be accomplished through the use of helicopters, and/or a mainline/belay line system combined with various forms of offsets. It is that rare 1% of the time that a highline might be needed. Typically, highlines are incorporated where a long expanse or swiftwater must be negotiated for the successful extrication of the victim.
Highlines are almost always a last resort option. The good side of highlines is that it is a viable option; the bad side is that there are numerous reasons why not to do one. If over tensioning and rope abrasion are the archenemies of rope rescue operations than consider these two evils the devil incarnate to a highline.
By its very nature, highlines go against most conventional rules of safe anchor building. In most cases, we try to keep the angle between multi-point anchors 90% or less, at 120 degrees the force at each anchor equals the weight of the load. With highlines, you are looking at a vector angle of 150 degrees and up. This alone will multiply (with the rescue load in the middle of the trackline) the weight of the load anywhere from 2 times at 150 degrees to 11 times at 175 degrees at each anchor!
Because of this tremendous stress highlines put on the anchors, here are some key principles that must be included in the construction of highlines:
Anchors must be bombproof.
Full strength of the trackline must be utilized by eliminating all knots, and all sharp bends.
All knots on the control lines must be bypassed.
Maintaining a pulley tension system to the highlines utilizing a “slipping clutch” (or safety fuse) in the form of system prusiks. (8mm, 3-wrap)
Incorporate a carriage system supporting the load.
As with any rope rescue operation, highlines even more so, must be able to pass the “whistle test” and the “critical point test”.
Stages of Highline Operations Highline operations consist of five major stages, they are:
Spanning the Gap
Construction of the high directionals
Construction and Tensioning of the Trackline
Construction of the tagline/belay systems
Construction of the carriage Break down.
Spanning the Gap
As stated earlier, the initial action of a highline operation is getting the various ropes across the expanse. Typically the order of lines used is; the pilot line which pulls the messenger line which pulls the opposite side tagline.
There are a number of ways to get the pilot line across, including something as simple as a hand-thrown weighted object with the pilot line attached.. To negotiate a long horizontal expanse, a more sophisticated delivery system must be deployed, namely the use of a crossbow, a line gun, or a rocket delivery system.
The messenger cord is the second line pulled into place by the pilot line. Providing the messenger cord is twice the length of the expanse, it may become very useful as a means to transport various equipment back and forth between sides.
The messenger cord in turn pulls the first ½ inch system rope across, usually the opposite side tagline. The opposite side tagline will pull the trackline, the carriage end of the “control” side tagline, and a pulley.
Once the trackline is secured at both ends, the pulley will allow the control side to bring the carriage ends of both tag lines back to the control side for completion of the carriage system.
Construction and Tensioning of the Highline
There are immense forces generated at each end the highline, because of this it is imperative that all knots be eliminated from the highline, and that the highline not be over tensioned.
The highline must be one continuous rope and the opposite side must be anchored with a high strength tie-off.
The control side of the highline is typically finished off with an integral 3:1 MA. (Ganged systems are sometimes used, especially for bundled 2 and 4 rope highline systems.) This MA should include tandem prusiks at the ratchet pulley (This is the only time tandem prusiks should be incorporated in a mechanical advantage.) When pre-tensioning the highline, use only one person to pull on the equivalent of a 3:1 MA. Post tensioning of the highline the maximum number of haulers is dependent on the weight of the rescue load, the length of the highline, and the amount of desired percentage of sag.
Multiple Bundle Highlines/2 Rope, and 4 Rope Highlines
As stated earlier, one of the most critical points of a highline operation is the amount of tension at each anchor created by the vector force of the load. In pre-tensioning a single highline we would use a single person pulling on the 3:1 MA, this would allow for approximately a 10% sag with the load at the middle.
There may be situations that will not allow for this much sag i.e., swiftwater highline rescues. For these types of highlines where little sag is wanted, it would be very dangerous trying to remove the sag by increasing the tension. This problem is solved by the deployment of additional highline, also known as bundles.
Typically seen are 2 rope, and 4 rope highline. Keep in mind, that the sag is lessened by the addition of more highline to the bundle, the tension on each individual rope in the bundle is still going to be about the same.
Highline, Floating “A” Frame
The use of high directionals is a very important aspect in the construction of highlines, especially on the side the rescue package will be brought to.
The first option would be for a “natural” high directional, usually a tree, if this is not possible, the “A” frame makes a quick an easy to set-up alternative.
When used in this application, the “A” frame does not need to be guyed in the traditional manner as shown in chapter 5. After the trackline is constructed, lash the “A” frame together, hook a pulley to the trackline and connect it to the apex of the “A” frame while the “A” frame assembly is flat on the ground. The “A” frame can easily be vectored into place prior to the pre-tensioning of the trackline.
Once the “A” frame is upright, it is then guyed into place by employing two opposing system prusiks connected to the trackline on both sides of the pulley.
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Peace on your Days