Is this hinged collapsible clothesline design stable enough?

Question

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.

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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Answer 1

Suggested construction:

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.

Answer 2

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.

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).

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Alternative: Clothesline outside the railings

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

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

Answer 3

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,

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.

Answer 4

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.