The level of strength reduction can be substantial. In some cases, strength can be reduced by over 50 per cent. However, this will depend on many factors, including the type of knot, how the knot is tied, how neat it is, how the rope is loaded, the design of the rope and so on. Typical polyester or nylon ropes should be expected to retain 50 percent of original strength when knotted. Ropes made from HMPE or LCP type material for example Dyneema or Vectran should be assumed to retain only 40 percent of their strength when knotted, while Aramid ropes could retain as little as 30 per cent of their strength.
In contrast to these figures, a well spliced rope will typically retain 90 percent of its quoted strength. In fact, some ropes typically HMPE products are often quoted with spliced strength, as this is how the product is tested.
If strength of termination is critical then a splice is always the preferred choice. Share on linkedin LinkedIn. Share on email Email. See all results. Rescue Response Gear. Shop By. Brands Category Menu. Join our newsletter. Follow Us. This website uses cookies to improve your experience. This is because knots cause tight bends in the rope whose outer circumference is greater than the inner part.
This causes the rope to load unevenly, technically loading the rope across it's width when under tension, instead of it's length which completely undermines it's strength. This uneven loading is what makes all the knots that we use in tree care operations decrease the overall strength of the rope at the knot. Let's take a look at some common knots and how their strength is affected by tying and then loading them.
The King of Knots! The bowline is use to attach the rope to the tree for base anchors in SRS climbing systems or for attaching the rigging line to limbs or logs being lowered from the tree. The Clove Hitch is also used in closed climbing systems to attach the rope to the climber's harness before tying their friction hitch. Every rope is weakened by tying a knot! If you have a damaged usually frayed section of rope then it is possible to knot in another section of rope to take the load.
Typically you would do this with a sheepshank or one of its variants. In this case the knotted rope will be stronger than before, because its strength was seriously limited by the damaged section.
Now the damaged section is no longer taking the strain, you've fixed that weakest link. The answers above are already very complete considering strength.
There is however one other point that I'd like to add. If you have a knot in a rope that gets wet, the knot will stay wet longer than the rest of the rope. This will allow mold to grow more easily in the knot, where it has a wet and probably warm place to stay and grow. Of course it goes without saying that mold will weaken your rope.
Side remark: you don't need knots to grow mold; in time even a straight rope will probably start growing mold. Another point I'd like to make is that for the application you are mentioning it probably will not matter since the weight of your clothes is not that large compared to the breaking strength of rope. Of course if you really put a lot of tension on your system this can start to become relevant.
Finally the rope will probably be hanging permanently outside exposing it to UV and hence UV damage on your rope. Conclusion: If you'd like to put knots in your rope you can do this for a regular clothesline. Your biggest enemies will probably still be moisture and UV damage, which will cause the rope to decay over time. The system with knots will probably not last quite as long as the system without knots. But from practical experience I knot that the difference in lifetime will be small.
With mono-filament fishing line, there are a number of issues which cause the knot to be weaker than the line. With heavier gauge of twisted rope this may be less, but is still real. The uneven tension in the knot will cause distortion and stress to not be evenly distributed, causing uneven wear to the line or rope.
Most knots have some level of slippage when stress is applied. The slippage will cause the rope or line to rub while under stress and slowly cut, weakening the line. Some of this varies by diameter, with different configurations favoring different knots due to line slippage, so fishing knots that are relatively strong might not be good choices for braided lines.
That said, the general principle remains that a knotted line will be weaker than one with no knots. An exception might be forming a compound rope by knotting more than one line together in parallel which could be stronger than a single line but more stable than multiple lines simply looped together.
A curvature in the rope causes the tensile strength of a rope to decrease. The strongest configuration is the one where the stress distribution across the rope cross-section is close to uniform, i.
When the rope has a knot it may seem more stable, simply because the overall rope is thicker. However the rope will usually not break in the knot, but at the end of one, where there is a curvature. If you are looking for data on the topic there are two main applications: industrial ropes and steel wires and slacklining.
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