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I'm new to this forum. I'm not sure if I'm supposed to be asking questions about clothesline here, but I didn't find any forum in StackExchange that was something like 'DIY'. So, I suppose it's okay.

I've recently built my own clothesline using rope and a tightener. It worked pretty well for some weeks but I now see that it is sagging.

This is how it looked when I built it for the first time:

enter image description here

enter image description here

And this is how it looks now:

enter image description here

When I built it, I tightened it as much as I could, but still, it ended up deformed this way.

Do you know what I can do? Should I change the rope maybe? Is it the tightener that I used?

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They always sag , even steel . The only difference is the amount . For steel cables you would need instruments to measure the few thousandths of an inch of sag. The shape of the sag is called a "catenary" . You can find math equations to calculate the sag depending on the material and tension.

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    And, for those who are interested, this is due to a combination of the fact that you cannot get any rope or cable completely taut and the fact that it will stretch under it’s own weight. – Austin Hemmelgarn Nov 13 '20 at 0:26
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    no, in this case the sag has increased since the initial deployment. The tension in the rope has reduced for some reason, e.g. the rope has stretched. It's probably just stretched or loosened from having stuff hanging on it. – crobar Nov 13 '20 at 10:40
  • It's obviously sagging a lot more in the last picture than in the first picture. The question is not asking why it sags but why it sags so much more. – user253751 Nov 13 '20 at 17:23
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As has been pointed out by blacksmith37 every rope stretches and snags a bit. That said, there is some possible solutions to your problem

  1. Take a low stretch material. There is cordelettes with a dyneema core which barely stretch. On the other hand this seems a bit excessive for hanging your clothes
  2. Pre-stretch your cord. Fit it somewhere and hang something heavy on it for a longer time. Once it has stretched, place it on your hanger and tighten it. Now it can no longer stretch
  3. Add some active tightening by putting a spring or a counterweight or whater that tightens the cord.
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    Adding a fourth item to the list: If purchasing a rope/cord made of synthetic fibers, look for one which is designed to be weather resistant. Many synthetic fibers are weakened by water (nylon is notorious for this) or UV exposure. – Austin Hemmelgarn Nov 13 '20 at 0:28
  • Even with all of these factors, you'd still have some degree of stretch. The only way to avoid stretch would be to get rid of the gravitational force pulling it down, or make the tension force along the cable literally infinite. – nick012000 Nov 13 '20 at 1:15
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    @nick012000: More prosaically, you can tighten it until it snaps, at which point it is no longer sagging. – Kevin Nov 13 '20 at 3:23
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    @Kevin Even if it was made of a magical material that had infinite tensile strength, it still would sag until you put infinite force on it. – nick012000 Nov 13 '20 at 4:27
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    Dyneema rope of the size shown by OP will survive enough tension to pull those flimsy steel frames out of the wall without any magic, probably including the wall too... But on positive side you'd be able to hang out closes without taking people out of them just fine... :) – Alexei Levenkov Nov 13 '20 at 5:24
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My experience is totally different than the other answers here, yes every rope stretches but usually the problem lies at the wall mount - it is flexible and bends easily as you tighten the ropes.

This is easily visible - you tighten the closest line to the wall, then as you go to the outer ones, where the torque created is bigger, the inner ones will quickly sag. If you go the other way the effect will be less.

What can be done? You can either fix the mount to the side walls or add some sturdy support between the mounts. Some wall mounts comes as a rectangular metal frame but they might still be somewhat flexible in the middle lines.

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    I also had immediate suspicion of the mounting strategy shown in the pictures. I can't think of a worse way to have the brackets set up, they are certain to flex towards each other.m This is the best answer. – Jimmy Fix-it Nov 13 '20 at 17:15
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There are cables purposely manufactured for that use. They are basically steel cables with a plastic sheath (see picture).

Clothes cable

They are cheap and durable, and have a low amount of sagging. To tighten them properly, as fgysin suggests, a turnbuckle would be of great use.

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As has been answered by others, every kind of rope will sag.

I suggest you use some tighteners which will allow you to increase tension once this happens. You will then have to do this a couple of times until the rope has mostly stretched out, and then the additional sag should be minimal.

Also note, that what you used is not actually a device to tighten ropes - it will not allow you to tighten the rope, but will simply make a solid connection between two strands (normally it is used to connect steel cables).

My suggestion would be to use a turnbuckle or a similar device, see this google search for sample images.

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If one stretches a rope between two points some distance X apart, hangs a weight W in the middle, and wishes to prevent it from sagging by more than some distance Y, the tension on the rope will need to be WX/2Y. If one wants to have a 2m rope sag by less than 1mm while supporting a 1kg weight, the tension on the rope to support that weight would have to be 1000kg beyond what would be needed for the rope to support itself. Unless both the rope and the restraints are very strong, that isn't going to work. What will generally happen instead is that the rope will sag to the point that WX/2Y becomes reasonable or something breaks.

If one needs to have a suspended rope which is flat and level, the way to do that is to do what electric railways do with their power cables: have a supporting rope which sags by a significant but known amount, and then have suspension ties connect that to a lower rope. By making the suspension ties longer near the edges than in the middle, the lower rope can be made flat and level without requiring any of the ropes to support particularly excessive tension.

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  • Look at the pictures. In the first picture there is no load and no noticeable sag. In the last picture there is no load and there is noticeable sag. The question is: why? – user253751 Nov 13 '20 at 17:24
  • @user253751: Have loads been applied to it in the interim? Applying a non-trivial load to the middle of a straight taut line will increase the tension by an amount which exceeds the weight of the load by multiple orders of magnitude unless--as is usually the case--something stretches or breaks. Sagging may not be aesthetically appealing, but doubling the amount of sag one is willing to accept will cut the tension roughly in half. I've seen videos of people who have pulled down porches as a result of trying too hard to prevent lines from sagging. – supercat Nov 13 '20 at 17:45
  • So you are saying it has stretched. – user253751 Nov 13 '20 at 17:58
  • @user253751: And also that sagging is a good thing. If a clothes line sags after it is used, that means that there was dangerously little slack in it, resulting in excessive tension, but the slack has been increased to reduce tension. If one takes in the slack and again applies a load, the clothes line will have to stretch more, and end up sagging again unless the line reaches a deformation limit that either causes it to give way, or apply more tension to its supports, possibly causing them (or the building in which they're affixed!) to give way. – supercat Nov 13 '20 at 18:25

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