Every rope has a “breaking strength,” which means that if you place a heavy enough strain on a rope then it will eventually break. The Safe Working Load of a rope is generally considered to be one-fifth of the rope’s breaking strength.
So, how is the average person going to know which knots are the best and safest to use? After all, using the wrong knot, or using a poorly-tied knot, has led to many accidents, injuries, deaths, and destruction of property.
Knots almost always lower the strength of a rope, sometimes by 25%, 50%, or more.
The highest-rated rope has a safe working load of 450 pounds, but most ropes are rated at under 300 pounds. If a rope has a Safe Working Load of 300 pounds, then we might assume that the rope should be okay to use for lifting an injured 200-pound man to safety, right? But if we tie a knot in the rope to help lift an injured man, and if the strength of that knot is rated at 60%, then the Safe Working Load of our rope has suddenly been reduced to 180 pounds (60% of 300 pounds). The injured 200-pound man is now beyond the Safe Working Load of our rope because of the knot that we tied.
This is worth bearing in mind!
Modern ropes used by rock climbers often have a breaking strength of several thousand pounds when they are new – but they deterioate with wear and tear and long-term storage. What it once was is not what it will be after use.
Don’t be blasé about your rope. It is probably the most important piece of equipment you have got. Your life depends on it. Look after it and be aware of its limitations.
Some Basic Terminology to be Aware of:
When a rope circles around and then crosses over itself, this is often referred to as a “loop“:
A “bight” is essentially an open loop:
After you tie a knot, it is important to “dress” the knot properly. This means making sure that all parts of the knot are in the right place and that the rope doesn’t cross itself unnecessarily. Each time a section of rope is sharply bent over something (such as another part of the rope), this can stress and tear some rope fibers. This is why it is important to dress the knot properly, because otherwise you are weakening the rope without realizing it, and in some cases you might be trusting your life or property to a significantly weaker rope than you had expected. In the pictures below, the first one shows an improperly-dressed knot and the second one shows the same knot which is properly dressed:
Again, if a knot is not properly dressed then it can weaken the rope more than a properly-dressed knot will. Also, the knot should be “set” by being tightened before it is used. Otherwise the knot might “slip” or “spill” or “capsize” and become unstable or fall apart, which can potentially be disastrous.
Knowing the best knot to use and properly tying it and properly dressing it and properly setting it can save your life or save someone else’s life, or protect your valuable possessions from damage.
One knot you should know for rock climbing is the Figure of Eight knot. Thanks to Howcast for this simple but clear video.
And thank you too to Dave at www.layhands.com for a lot of this very pertinent information.