I need help validating my clothesline design. It'll be on our deck for convenience (I don't want to lug a heavy basket of wet laundry down to the backyard). I want it to be collapsible so we can hide it if we ever have guests again. And, if we have to sell the house to someone who doesn't appreciate clotheslines, we'll just unscrew the hinges and take the whole thing down with minimal damage to the railings.

The idea is, the clothesline posts will be attached to the top of the deck railings with hinges. When in use, the bottom ends of the posts will simply sit on the deck railings. When we need to hide them, we'll simply fold them back so they hang upside down behind the railings.

enter image description here

My questions are specifically about the stability of this design. I'm only expecting less than 15 lbs of load, consisting of 2 king-size sheets and up to 2 bath towels, so maybe I'm overthinking this, but better safe than sorry. By which I mean, better to ask now and look like the beginner that I am, than spend 5 hours putting it together and have it sag or bend or fall apart 😬

In my mind, these are the Bad Things™ that can happen:

  • The hinges may be pulled out by heavy wet laundry pulling on the top of the posts. I read that screws can withstand shear forces of 600 lbs so I don't think this is likely.

  • The hinge itself may pull itself out of shape, or even come apart, from bearing the weight of the posts when the posts are stowed. That would actually be dangerous, since the posts can then fall on someone under the deck. And obviously hinges are not meant to be used like this - not as part of a set, and bearing forces that pull them apart. But then I think the posts will only weigh 40 lbs or less, and in any case, I think I can work around this by simply nailing some blocks of wood to the railings under the posts when they're stowed, to bear the weight of the posts instead of the hinges.

  • The posts may lean inward when there's laundry on the lines, since they're just sitting on the railings with no fasteners. Is this a risk with the center post being a 4x4 (so there's a decent amount of surface for it to sit on)? I can also add shims underneath to counter any leaning.

So, what do you think? Are there other glaring design flaws I'm not thinking of?

Thanks all in advance!

EDIT Aug 2, 2020: Some people have suggested some intriguing ideas, including a prop in the middle of the line and a telescoping post. I am interested in all those ideas, but could you please include some details on the materials and hardware I need to implement them? I am a DIY beginner, and this project is apparently far more demanding, engineering-wise, than I'd estimated. Who knew hanging 13 lbs of sheets to dry would be this complicated?

Also, the 13 lbs estimate is from Googling the weights of the sheets and towels, cotton absorbency and washer spin cycle water extraction rates. I am aware that wet laundry weighs more than dry laundry.

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    A foldaway clothesline frame looks like a good idea in general, but the design as you have drawn it will rip the cap rails right off. You need a design with deeper bracing against the deck railings. – A. I. Breveleri Aug 1 at 1:19
  • @A.I.Breveleri Thanks. JRaef's answer brought that up too, and I'm definitely going to address that. I'm thinking of sistering the thick railing with an extra post and toenailing its ends to the cap railing and floorboard. Would that work? – Bad Request Aug 1 at 1:30
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    those clotheslines are too low ... clothes will touch the deck ... wind will make the clothes wipe the BBQ ... also, no access to barby when clothes are up – jsotola Aug 1 at 1:36
  • 50 lb of wet clothes will produce about a 300 lb tension on the cable due to gravity ... add wind to that – jsotola Aug 1 at 1:49
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    A prop in the middle would considerably reduce the tension and raise the textiles. It stands alone due to friction at the (rubber) foot, and under the lines. – Paul_Pedant Aug 1 at 18:42

Suggested construction:

deck folding clothesline

This spreads the torsional load over the entire banister railing instead of stressing only the cap or top rail.

If there's any bending at the hinge, or other distortion, it will be confined to the added pieces and will leave your existing railing unaffected.

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Just one detail: the horizontal force does not need to be tremendous and you can in fact adjust/limit it.

The force the clothesline transmits to the post is in direction of the angle the clothesline has directly at the post, α. We can decompose it into a vertical component Fv that adds up (for both posts) to the gravitational force of the combined mass of clothesline and clothes. So, say, 100 N for 10 kg of clothes, clothesline and some water. If you hang your clothes "symmetrically" (i.e. the center of mass is in the middle of the clothesline), Fv = 50 N on each side.

The horizontal force Fh is Fv ⋅ tan α. E.g. if α = 45°, the horizontal force will be equal to the vertical force. If α is larger than 45° (the line is sagging less), the horizontal force is larger than the vertical force e.g about twice as large at α ≈ 60°, 3 times as large at α = 70°.

Of course, you "pay" for this low horizontal force by needing a higher pole (which also means more leverage).

As a back-of-the-envelope estimation (image below) I put 1 m of railing plus 1 m post at a distance of 5.7 m, accepting the clothesline to sag 1 m, i.e. down to the railing. That would put the "working height" between 1 m (like a standing clothesline) to 2 m which should be doable. The resulting maximum angle for "symmetric load" would result in a 70° angle which gives us Fh ≈ 3 Fv with the clothesline length being 1.06 ⋅ the distance between the posts (so an additional 35 cm ≈ 14"), the momentum at the joint between lower/upper part of the railing would be 150 Nm (i.e. the vertical equvalent of hanging 15 kg at a lever of 1 m length) - which should be well within the capabilities of many hinges. And a railing should certainly be able to withold this horizontal leverage - though the torsion on the cap rail may still be too high in your initial design.

Hanging clothes throughout the full length of the clothesline would ease the inward force since it causes a smaller α right at the post and a more flat clothesline in the middle.

sagging clothesline

Final thoughts:

  • If OTOH you insist on the clothesline almost not sagging, the horizontal force will increase tremendously.
  • A post in the middle (tie to sunshade stand?) would help a lot, in a similar back-of-the-envelope calculation halving the sag and at the same time also halving the horizontal force (since it would take half of the total vertical force.
  • I'd have estimated 7 kg of clothes (dry weight) to need 1 or maybe 2 lengths of your clothesline, but certainly less than 4 lengths. But I may be quite off here.
    The comment about the sheets makes a whole lot of sense - though I find hanging sheets in double (i.e over one line) works fine here (Germany) - already a little bit of wind and more distance than on a clothes stand make drying a whole lot faster anyways.
  • With a sagging line, clothespins are your friend.
  • Since you'll anyways remove the clothesline you can go for a braided cord rather than the smooth-coated variety (which is easy to clean if the clothesline stays outdoors). Braided cord may be far less slippery (I usually use "Reepschnur" [don't know in English, it's the kind of nylon cord one uses e.g. for Prusiks] since I have anyways have suitable lengths of that around).

Alternative: Clothesline outside the railings

You could also consider putting a permanent clothesline (blue) outside the railings (black):

clothesline outside railings

Such a construction with the lines anchored to railing posts easily allows a whole lot of tension (so not much sagging) since the horizontal forces are quite nicely countered.

  • The ones I've seen (e.g. outside my window when I was living in Italy) were usually steel constructions - but you could also use wood to be consistent with your railing.

  • Sheets touching the railing: depending on the wind, this may happen. However, I'd say one could have the outermost line maybe 50 - 60 cm outside the inner end of the railing (will be tedious, but/and train your arms and back...). The further out, the less risk of the sheet touching. Also depends on what is below: it may be better or worse to hang the sheet single or doubled up.
    It may be a vialble compromise to hose/wipe down the parts of the railing that may be touched, say, once a year or so. You'd certainly want to wipe the top of the railing where the wet clothes may touch

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    Yes!! Your calculations match both my intuition, and the tension physics I read up on last night. Very nicely laid out too, thanks! Now I can use this model to minimum acceptable sag (I do want as little sag as possible since I’m drying sheets, which would slide into a pile toward the center with too much sag). – Bad Request Aug 1 at 15:07
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    The 4 lengths are so I can dry one sheet on each pair and have air circulation underneath them :) – Bad Request Aug 1 at 15:08
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    If one wants to have a horizontal hanging rope, the way to do that is with a double suspended rope design, such as used by electric railways. – supercat Aug 2 at 3:42
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    @supercat: it's a valid alternative to "intermediate posts" that may result in better "horizontalness", but care is needed or it will be even more cumbersome for hanging sheets than posts. – cbeleites unhappy with SX Aug 3 at 12:11
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    @cbeleitesunhappywithSX: Care is needed with the design, but I was suggesting it as an alternative that might (or might not) be useful. One of my concerns is to limit horizontal loading even under unexpected-stress conditions. If horizontal forces can be reasonably limited, it may be practical to use a counterweight and pulley to hold the lines, so that if someone trips and grabs the clothes, the counterweight could help slow their fall without putting undue stress on the railing. – supercat Aug 3 at 15:22

the clothes-line with 6 inches of droop over 10 feet of span multiplies the weight of the clothes by about 20 to get the tension in the rope.

The 4 feet tall 4 inch wide folding arm multiplies by another factor of twelve

Your hinges need to withstand 50x20x12 pounds in tension 12000 pounds, without using steel and posts with welded hinges that's not going to happen.

I'd go with telescoping instead of folding, enter image description here

the triangle is to hold the post up in its high position. the circle stops the post from tipping inwards (the rope will stop it from tipping outwardsm, or to could add another bracket)

The circle could also be a wheel could have a rope around it to the bottom of the post for a counterweight to make the post easier to lift.

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  • Couple questions. 1. Could you please explain where the numbers 40 and 12 come from? 2. Isn't 6" a rather excessive sag estimate? That's about 45º right? I'll have tensioners so I hope not to have that much sag. 3. How does it change the calculations if the load is spread over 4 lines instead of 1 (as shown in my drawing, though admittedly not clearly)? – Bad Request Aug 1 at 3:13
  • 4 feet of 4" pole is 12 time longer than it is wide. less sag means more tension, 6" is about the max acceptable 1 line or 4 makes no difference all the forces add up the same. 40 is wrong should be 20 as the sag is in the middle still massive forces. – Jasen Aug 1 at 3:17
  • OK thanks. Some more questions if you don’t mind: 1. What hardware do I need to build a telescoping post? 2. In your drawing, those 12000 lbs of tension will be borne by the triangle wedge, right? How should that wedge be attached and how do we know it can withstand more force than the hinge? – Bad Request Aug 1 at 3:22
  • One more :) 50 lbs is actually a very conservative estimate. The actual load is a king-size sheet set and up to 2 bath towels, all spun dry. I just Googled their weights, cotton absorbency and washer spin cycle water extraction rates. Apparently the realistic load is about 12 lbs. That makes the tension 3000 lbs. Still too much for the hinge? – Bad Request Aug 1 at 3:33
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    @BadRequest 50lb is only "conservative" until somebody slips or trips (e.g. by stepping backwards into a laundry basket on the deck!), instinctively grabs the line to stop themselves falling, applies a 250lb load to it. and ends up on the ground underneath a pile of broken wood. – alephzero Aug 1 at 12:56

What are you going to use as an upright member on the posts? I would do it with a 4x4 because it would add some stability when resting on top of the rail while in use. Your laundry is going to want to pull the posts in toward each other. That will put a lot of strain on the hinges, which themselves are probably fine, but will be pulling on the screws and the rails very hard. In fact, the rails may twist on you so I would also put another vertical post under the rail on the near side one and use a "strap hinge" that would go down into both posts. enter image description here

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  • By "upright member" do you mean the center of the post that sits on the railing? If so then yeah, it'll be a 4x4 as described in my drawing. The hinges will be the 4" wide outdoor type, so the pulling will be distributed over 4" and 4 screws. Does that seem OK to you? Twisting railings are a real concern, especially with our deck being so old as you can see, so thanks for bringing that up! – Bad Request Aug 1 at 0:53
  • Also, if I understand you correctly, are you suggesting a strap hinge because it's long enough to reach both the clothesline post, the top railing, and the extra vertical post? That'd be at the expense of it being skinnier than the rectangular hinge I was considering though. Perhaps I can just join the top railing to the extra post with a toenailed screw? – Bad Request Aug 1 at 1:15
  • the strap hinge is good because the wood is weaker near the cut end and the strap hingr has two screws that are not near the weak part. however if the screws are good for 600 pounds shear force it still might not be strong enough, – Jasen Aug 1 at 9:54

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