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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.

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.

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?

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.

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.

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.

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).

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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.

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.

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.

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.

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.

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.

You can sleeve the cable in pvc pipe or something.

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.

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...

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.

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.

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

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

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.

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.

no

very informative answer

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.

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.

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.

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

Scaffold pole. Cement it in. Couple of struts.

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.

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.

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.

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?

I copied what this guy did for the cable issue: https://www.youtube.com/watch?v=tZVidnXewBQ

Also check this video out: https://www.youtube.com/watch?v=a1KPl-M-dpM&t=0s

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.

This article covers a bunch of stuff you'll need to know and calculate for this. I think your 4 6x6 idea may fit with this

https://www.ziplinegear.com/pages/how-to-build-a-zip-line-section-one-concepts

I believe you'll need to figure in a lot more wood than you may be thinking. It will probably need a platform at one or both ends, and guy anchor posts at each end.

https://www.americanpoleandtimber.com/wood-timber-products/challenge-course-zip-lines-ropes-course-materials/ looks like they have what you're looking for. They say they have posts up to 52' long and 20" diameter. How much they charge I have no idea.

That’s a great website

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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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

Can you use a telephone pole?

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.

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

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

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

The stacked 2x12's would be stronger.

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?

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

You can find used telephone poles on FB Marketplace

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

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

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.

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.