Roco Rescue



Why Knot?

Thursday, December 01, 2016

By Pat Furr, Safety Officer & VPP Coordinator for Roco Rescue, Inc.

As rescuers, we all have our favorite knots and our favorite ways of tying them. Depending on the application, there may be several knots to choose from that will perform slightly differently in terms of efficiency or knot strength. You can go online and order any number of books ranging from a couple of pages thick to 2’ thick with hundreds of knots in it. The trick is to decide what applications you will need to perform with your ropes and knots. If you don’t need to shorten a rope, then you don’t need to know how to tie a sheepshank. Or, if you use manufactured harnesses, then a tied Swiss Seat is not a needed skill in your inventory.

For the most part, we can break applications into 6 categories for rescue purposes: 

1) Knots that form a permanent loop in the end of a rope (Ex. Figure-8 on-a-bight)
2) Knots to tie around objects (Ex. Bowline)
3) Knots to join ropes together (Ex. Square Knot)
4) Knots tied in the middle of ropes (Ex. Butterfly)
5) Hitches binding and adjustable (Ex. Prusik Wrap or Clove)
6) Utility knots (Ex. Daisy Chain)

Whenever we tie a knot in a line we lose some of the efficiency in the rope or webbing we are using. Generally, the more acute the first bend in the knot, the more efficiency is lost.

Other factors such as angle deflection, direction of pull, and rope construction all have effects on a knot’s efficiency. Then, there’s the type of load the knot will see (two directions or three directions). The direction and critical angle applied forces may change the efficiency rating of a knot greatly. In rescue, we try to use knots with fairly small efficiency losses, generally between 18-37%.

There are some other considerations beyond knot strength when choosing which knot to use for any particular application.

Ease of Tying

In addition to knot efficiency (strength), we also must think about many other things such as ease of tying especially in those hard to access places where you wish you had more Gumby genes. Where and under what circumstances will you need to be tying the knot? Will it need to be tied one-handed? Is speed a consideration? Take a calf roper, for example, he needs a knot he can tie quickly and securely. Would you be able to tie a Prusik on line for self-rescue with one hand if the other is stuck in the device? What about an emergency situation where you might need to bail out a window while blinded by smoke?

Say you want to clip into a fixed rope but need to do it one-handed? The Clove Hitch will be much easier to tie into a carabiner one-handed than most loop knots. Not only that, if you need to adjust your position after clipping in, the Clove Hitch is easily adjusted one-handed.

Ease of Untying

Not only ease of tying, but ease of untying a knot should be thought through, especially with wet rope or heavy loads. Once the knot gets loaded – or if it sees a heavy or shock load – will you be able to get the knot untied? Will you need to use a tool like the marlin-spike to get your loaded knot untied? How often will you be tying and untying the knot? Will the knot be wet or dirty? (Example: a loaded Bowline is easy to untie, while the Figure-8 Bend is more difficult.)

Knot Security

Knot security must always be considered but this is especially true if the knot will be subjected to tension and slack repeatedly. Will the knot be able to untie itself if it is cycled between tension and slack? (i.e., Square Knot vs. Figure-8 Bend) We know that a Butterfly Knot performs much better than a Figure-8 on-a-Bight if the knot is to be pulled in more than two directions. But what about some of the lessons learned over time that we know will make a difference in which knot to select based on other considerations. How difficult is it to untie a Figure-8 on-a-Bight after it has been loaded wet vs. a Two Loop Figure-8?

Tying a fixed line for a rappel? There are several choices to tie a fixed line instead of clipping it to an anchor strap. The Bowline, Clove Hitch, Figure-8 Follow-Through will all work, but if the line goes in and out of tension, how secure is the Clove Hitch compared to the Bowline or Figure-8? If security isn’t a concern, it will be easier to untie the Clove Hitch after it has been loaded followed by the Bowline, with the Figure-8 probably being the most difficult to untie, especially if the rope is wet.

Tying an anchor around a very large object? You will use up a lot more rope and time tying a Clove Hitch vs. a Figure-8 Follow-Through or a Bowline.

How will a knot handle a sustained load or shock load?

If you anticipate a heavy load on a Prusik Knot, consider making it a triple wrap instead of double. This will give you more friction, and it will definitely make it easier to untie later on. A little trick I use to loosen a loaded Prusik is to “push the bar.” By that, I mean to push the section of the knot that runs parallel to the rope that it is tied around away from the main line, which will loosen the knot.

The Water Knot is great for tying webbing together to form a runner or sling. But if it is really loaded, it can be a bear to untie. Try this, turn the knot so it is oriented vertically along its axis and place it between the palms of your hands. Rub your palms together squeezing on the knot and really be aggressive. After a few seconds, see if you are able to work a little looseness into the knot to start untying it. Same thing with a Figure-8 on-a-Bight, grasp the knot with both hands beside each other with half of the knot in each hand. Then, bend the knot back and forth as if you were activating a chem-light. Do this several times and see if you are able to milk a little slack into one side of the knot to start working it loose. Try to push slack into the knot instead of pulling the knot apart. Attack different parts of the knot until you see some movement.

Fighting untying knots?

If you are fighting untying knots on a regular basis, it may be time to add a marlin spike to your kit. A marlin spike is a tapered tool that finishes with a blunt or flat tip. They have been around since ancient times and may be useful to get that first bit of looseness into the tight knot. The warning here is to never place the knot in a position that the spike could slip and puncture your leg or arm, always push the spike away from your body.

If you know you’re going to really load up your knot and especially if the rope is wet, consider clipping a carabiner into the bends of your knot between the lays. This works really well for the Figure-8 on-a-bight or follow-through. Once you are done with that knot, remove the carabiner – this may provide enough slack to work the knot out.

We generally advocate stuffing rope into a bag and working out of the bag, but sometimes we “coil” the rope to go from point A to point B. How often has this led to a bird’s nest of rope? To help prevent a coiled rope from tangling, hold the coil up in one arm and let it hang free. Uncoil the rope with the other hand not allowing the lines to cross. By holding the coil up, gravity will show you which sections are crossing. You will then be able to keep the line straighter than if you dropped the entire coil to the ground and just started pulling rope.

So, you can see there is a lot to think about and consider when choosing what knot you should use and why. As we said earlier, there are hundreds of knots to choose from and many of them do the same jobs. And many are called different names in different books. The key is to identify the category, the application and the circumstances where the knot will be used. Then consider the above and you should be able to identify the proper knot for the job at hand.

Visit our Resources page for videos on knot tying and much more!

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