ZipLine Post

Submitted by CvilleHokie605 t3_zanra4 in DIY

Hey there. Looking from some advice on a zipline post size/build. I plan to put in a zip line for my kids with a weight limit of up to 250lbs which will be anchored on the lower side by a mature tree after traveling ~225ft dropping ~20/25ft. But on the higher side I don't have anything to anchor it to. I've been reading the product directions that a 12" diameter post 12' tall with 4' in the ground is ideal. But no where I've contacted sells such a large item. Enter the internet where I've seen people claim to use one 12' tall 6x6, several 2x6s glued and screwed together, or various other forms of combined lumber to get closer to something kind of equivalent to a 12" diameter behemoth. Any chance there are some strong/expert opinions here as to what is the ideal way to construct the anchor for high side of such a zipline that will last absent the 12' by 12" circular post?

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DrBouvenstein t1_iynjes8 wrote

FYI, that's too much of a drop. The max. slope for a zipline is 3' of vertical per 100' of horizontal with no brake, and 6' of vertical if you are using a proper brake:
https://www.ziplinegear.com/pages/how-to-build-a-zip-line-section-one-concepts#:~:text=ZIP%20LINE%20MUST%20NEVER%20EXCEED,MAY%20CAUSE%20INJURY%20OR%20DEATH.

Please do not make a death trap zipline that drops 25' over only 225 feet of vertical.

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CvilleHokie605 OP t1_iynkqak wrote

Appreciate this. I can adjust the drop with placement on the tree and the eventual termination platform. I'm just guessing at the drop right now anyway but will make proper calculations prior to eventual construction.

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chiffed t1_iyoanhf wrote

Adding to this, the horizontal tension is insane the less deflection in the highline. I would backstay the post to a forest of equalized ground anchors. Actually, I'd call up my rigging instructor. That's a big project with a bunch of failure modes. I wouldn't build it without him helping on the design.

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5degreenegativerake t1_iyngbnw wrote

How about just use a 6x6 and add guy wires behind it? The 6x6 is more than enough for the vertical load, it’s the crazy cable tension that requires such a stout pole.

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CvilleHokie605 OP t1_iynh1ne wrote

So would you drill a hole at say 7ft above the ground on the 6x6, run the wire through it and then anchor it a block of concrete on the ground? If it comes to that I guess I can go that direction but the presence of a wire going from the post to the ground with kids running around creates a possible injury risk.

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guccicolemane t1_iyo90wp wrote

no

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CvilleHokie605 OP t1_iyo95m1 wrote

very informative answer

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guccicolemane t1_iz0kgc8 wrote

googling zip line post and looking at the pictures would give you more help than making this post.

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CvilleHokie605 OP t1_iz12yc0 wrote

I've been looking at a lot of pictures and videos on this but wanted a discussion to go along with that to further my understanding of other's perspectives/solutions to this.

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guccicolemane t1_iz1gq8p wrote

https://i.pinimg.com/originals/59/6f/f6/596ff65c7f781fc1ec465c684993d452.jpg

https://i.pinimg.com/474x/f3/65/1e/f3651e10df09ebdf63acf701720416f9.jpg

or this https://everythingbackyard.net/wp-content/uploads/2017/10/dead-man-anchor.jpg

You dont want the cable to be stretched against a 90 degree corner on the wood post, so no hole in post with cable run through it. The cable elongates and retracts in size, it also stretches from bearing weight. Rubbing against the wood over time will deform it and weaken it. Putting it on an upside down pully as shown in one of the images above would work better. Or looping a chain around the post and then attaching to that with a hook and turn buckle would be what I prefer on my build. You tighten the turn buckle to account for any changes in cable length. It gets surprisingly smaller during colder times.

I prefer an A frame, you need 300lbs of concrete atleast in a 2ft radius of a foundation, buried about 2 feet of dirt so there is no movement. Two 2x4 kickers from the foundations out at a 45degree angle to the top of the 6x6 post.

Doing a single 6x6 post at a slight angle forwards with an pully at top, with the cable running over and behind, attaching to a 300+ lb concrete foundation buried a ways underground is the most efficient, I just dont like it for some reason.

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junkman21 t1_iynjmpu wrote

One way or another you will need to build a landing platform. And stairs. So, you can use the back two 6x6s as both a platform base and an anchor for the guy wires plus, possibly, flood lights.

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CvilleHokie605 OP t1_iynk1fn wrote

The start point doesn't need to be any higher so that doesn't need a landing platform (I'm in hill country so have plenty of fall already). I did plan to build a platform at the termination point though, but that has a tree so platform infrastructure doesn't give me anything I do not already have. Its the origination point that is tree-less.

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junkman21 t1_iynknif wrote

Oh, I see. This pole needs to be at the top. I'd still build a platform if I'm taking on a project like this. Even if it's only a platform 2 or 3 feet off the ground.

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CvilleHokie605 OP t1_iyo4iph wrote

What do you think about 4 6x6s glued and screwed together with the edges sanded round so as to not pinch the cable wrapped around them...

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junkman21 t1_iyoc3a4 wrote

I would think you would need through bolts, washers, and nuts if you want to go that route. You would also need to plane the two faces on each 6x6 that are getting glued for true adhesion.

Screws won't offer anything in terms of structural/shear strength. But I'm not a structural engineer and have never tried anything like this before.

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imnotsoho t1_iyp2v2t wrote

If you go to a professional lumber yard you can get larger beams, how about just 2 6x6 stacked in line with the cable? Guy wire to rear from top and brace in front with a small launch platform. Instead of wrapping the cable, drill a hole and terminate the cable on the uphill side. How are you going to avoid hitting the tree at the bottom?

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CvilleHokie605 OP t1_iyp6te2 wrote

My chosen system has a spring break. What is stronger I wonder: 4 to 6 ea of 2x12s thin side facing the termination point with the line wrapped around them like in the video another guy posted here, or two 6x6s in line with the line through them. Hmm

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5degreenegativerake t1_iyno9cc wrote

You can sleeve the cable in pvc pipe or something.

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tilhow2reddit t1_iyo80gj wrote

Iron Pipe would be my choice, a cable with that much tension on it could split PVC, and possibly split the post under load, and nobody wants that.

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5degreenegativerake t1_iyofyu3 wrote

I was talking about sleeving the guy wires so kids don’t clothesline themselves so bad. On the 6x6 I think I would just run the cable through a drilled hole near top.

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tilhow2reddit t1_iyo7v9s wrote

If you're going to run the cable through the 6x6 post like that I would drill an oversized hole and line it with a bit of iron pipe and run the cable through that, just to reduce the risk of the post splitting because of the cable/tension/etc. May even consider putting in some kind of brackets to reinforce that part of the post to keep it structurally sound.

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CvilleHokie605 OP t1_iyo81l2 wrote

What about 4 6x6s and run the line around them instead of through a single 6x6?

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tilhow2reddit t1_iyo8g6z wrote

I don't really see an issue there, but I'd probably still drill and all thread those posts together so they were acting as 1 solid piece, but that certainly seems like an option.

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CvilleHokie605 OP t1_iyo8ymg wrote

Oh yea, I would wood glue them together and then look for some kind of bolt to run through them to connect them all together, or an appropriate tie/mend plate or strong tie product I guess.

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NETSPLlT t1_iynzvsn wrote

I like compression, and would have wooden or steel beams suporting the front side. A set of two on angle, so as to not overly interfere with zippers.

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nah-meh-stay t1_iymwact wrote

Are there any telephone poles being replaced near you? Utility contractors can help find those.

You might be able to use a smaller diameter with steel post.

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CvilleHokie605 OP t1_iymxks2 wrote

Not that I'm aware of. I also do not have a vehicle or flatbed big enough to transport something so large so getting someone to have, let alone deliver, said post is not going anywhere. I'll look into the steel post idea.

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[deleted] t1_iyn49fu wrote

Usually people just drag old utility poles with a chain. Had a friend do that when he built his pole barn.

Could you mount the high side to the tree instead? What about building a platform instead of a single pole?

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CvilleHokie605 OP t1_iyn6v9n wrote

Can't drag it on the road that way :(

Zero trees in the vicinity of the start area. I do have a playset but there are warnings about not connecting it to playsets as they are not usually sturdy enough. All the vertical posts on that are 4x4s and I'd bet they'd snap under the load. I don't really want to build a big structure, just looking to try and comply with the load requirements with a vertical substitute for the 12" diameter post.

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accountonbase t1_iyni3th wrote

You don't need to transport the pole intact, and rental trucks can be really cheap for a few hours. You would just need to find one and cut it into more manageable lengths for the truck.

Since they're usually 30-60 feet, even on the low end you could easily get two posts out of it. For example, this one is 35 feet and about 640 pounds. Even cutting it in half is manageable for you and two friends (ideally 3 and maybe even some pulleys or other assistance).

​

You might even be able to find somewhere nearby that you can buy them from, but for that you really might need to talk to a utility contractor, and at that point it's probably cheaper to ask if you can get one they're going to replace so they don't have to haul it away themselves.

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usedTP t1_iyoiikp wrote

My local utility keeps replaced poles and damaged poles in their yard just for this type of project. A chain saw and a truck is all you need.

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dbryan62 t1_iyobg19 wrote

Make sure you over engineer your anchors. What you’re playing with are called vector forces, and they increase exponentially. For example, if your track line is tensioned enough to provide a 170 degree angle from the load (straight line is 180, so almost straight), your anchors are now EACH receiving 574% of the load, or 1435 lbs each. This doesn’t include the dynamic forces created when your kids jump on the line.

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limitless__ t1_iyofg6j wrote

I don't know what you're going to use but please video the first time you do use it.

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microcozmchris t1_iypro8h wrote

Have somebody else video it. Otherwise, it probably won't get posted.

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flippy_flops t1_iyoiqg4 wrote

225' is a massive amount of tension.

I did a zip-line with no trees and had the same issue. Wood that size is hard to find and extremely expensive. Ended up buying four 2"x10"x16' and laminated them together with glue/clamps/nails. Then put them in a 6 foot hole filled with concrete. It's very important that the thin edge of each board is pointing towards the zip-line.

If you don't need the elevation, I'd keep the top post as low as possible to reduce the torque.

There are online calculators that will calculate the tension of your cable. Then another "beam deflection" calculator which will tell you how much your wood will bend under that load.

Also - I use services like justanswer.com to double check my work. It's a fast/cheap way to chat with an engineer.

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CvilleHokie605 OP t1_iyojjhf wrote

Honestly, this is the solution I was hoping someone would suggest. I might up that to 6 of them. How did you deal with cable pinching when running it around something square?

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flippy_flops t1_iyolfdx wrote

If you up the size, consider 2x12's instead of 2x10's. Also, laminating them together is easy but lifting the entire post into the hole is challenging - definitely something to think through. If you're close to home depot then I'd rent a lift. If you want a platform, I bought a 6' wide wooden spool on craigslist for $50.

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totallynotroyalty t1_iyo8b0i wrote

You could probably get your hands on an I-beam to use. Delivery would still require a special truck, though.

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WaningMime t1_iyofyaa wrote

Scaffold pole. Cement it in. Couple of struts.

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ezhammer t1_iyp9ao2 wrote

Can you use a telephone pole?

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CvilleHokie605 OP t1_iyp9jey wrote

That would be perfect, but so far I’ve whiffed on finding one. Gonna look into a few of the sourcing suggestion that others made though. I even have a huge lumber yard near me that said ‘we do not have that product’ when I asked for the 12” pole. Not sure I believe that.

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ezhammer t1_iypc6gi wrote

You can probably find a heavy walled steel pipe that would do the trick. Anything 8” diameter or bigger would work

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bms42 t1_iyq5uv8 wrote

2 or 3 2x12s laminated together and then oriented along the zipline path will be just as strong as a single 12" round pole.

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NotTheJason t1_iyqyfp4 wrote

Is there any way you can just use the terrain? Like anchor it into the hill top and just, you know , start your zip a little further down?

Do you actually need an extra 12' of elevation?

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CvilleHokie605 OP t1_iyqzot7 wrote

Unfortunately it’s not that hilly and that design wouldn’t work for my set up, but I appreciate the suggestion.

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sweatyCheez t1_iyrqhra wrote

You can find used telephone poles on FB Marketplace

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CvilleHokie605 OP t1_iys2zd8 wrote

Welcome that idea but just checked, zero anywhere near me.

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