Zip line | zipline (recreational) attachment technique?

Go2Know

Hello all!

I have been looking all over the net for info, and found this great forum. By searching and reading I have answered half of my question.

Here goes. I recently bought and installed a toy zip line for my five year old son. It's barely above the ground and is only thirty feet long. HE LOVES IT!! So do all the neighborhood kids. Also, every adult that sees it says the same thing I said the first time I saw him whoop with delight as he went. "How much weight does that thing hold, and can I do it?" Unfortunately the answer is 100 lbs. Only children and supermodels can ride it. Naturally now I have to build one for the big boys.

Turns out there are quite a few places on the net that sell all the gear you need for a pretty major zip line. I think I have most of it worked out except for the tree to tree attachment points. I'm going to span two Live Oaks that are approx 200 ft apart. I love these two giants and the last thing I want to do is harm either of them just to have a little silly fun. BTW I think you all would either laugh your heads off or shake them in disgust at the way most people that post their zip line installs on the net attach to their trees.

I'm going to build a free standing platform approx 20 ft high directly in front of tree number 1. From reading the forums here my plan is to through bolt a large branch (co-dominant trunk?) directly behind the platform. Very long eye-bolt, carefully aligned with cable run, non-dissimilar washer and nut to avoid corrosion, tightened cut and peened over.

My question is, what about tree number 2? this attachment will need to be lower and below the top of the single enormous trunk. (before anyone asks, yes there are mechanisms for slowing and stopping before splattering into tree number 2) Obviously I'm not going to drill all the way trough a tree trunk that's six to eight feet in diameter. Even if it were possible i just wouldn't do it. I'm not comfortable relying on a lag bolt. So, besides "don't do it" what do you all think?

Go2Know

What do you all think about using a cable "sling" around the trunk, as in this picture?



I'm woried that would kill the bark and harm the tree.

Eric Frei

What is the total weight in the system, that's cable and pulleys etc?

What tension will be put on the cable, the zip line will require tension to stop a lot of "sag" in the middle, perhaps 1000kg?

What diameter is the cable?

What diameter is the bolts?

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Cole

yeah what ekka said was all good well but your playing with your childrens lives here if your in the states i guess you could talk to sherrill tree and or check out their learning centre online and you can read a fair bit about ropes and that sort of stuff, maybe get a local arborist to do a VTA visual tree assesment too get a report on the tree's health etc. the old zip-line or flying fox whatever you call it isnt a simple as it sounds hey, certain pulleys have diffrent speed and load ratings. if there is rope anywhere is it going to remain in the weather it will not last as long etc etc..... lots to think about.

Go2Know

OK let's see...

What is the total weight in the system, that's cable and pulleys etc?
200 ft of Stainless 304 1/4 inch 7x19 cable approx 25 lbs, silly fat guy approx 225 lbs, pully approx 3 lbs, turnbuckles, harness, caribners, Lets round up and call it 300 lbs.


What tension will be put on the cable, the zip line will require tension to stop a lot of "sag" in the middle, perhaps 1000kg?
It will have to be tensioned but maybee not as much as one would expect. Less tension = faster ride. The heights of the tree attachent points can be adjusted to keep the low point / sag about 80% of the way to the second tree where there is a breaking block around the cable and bungie corded tangentialy to another tree to slows and stop the rider. Of course all of this will be tested with my own crash test dummy (six five gallon buckets of water attached to the pully) in order to fine tune both attachment heights and cable tension.

What diameter is the bolts?
For the conection to tree number 1, there is a trunk branch (sory if thats not the correct term) about 20 feet up that has a diameter of 21 inches. So, I plan on using a 5/8" by 24" eye-bolt.

The question remains, what is a good way of attaching to a huge tree trunk without hurting the tree too much?

Eric Frei

You'll need a fair bit of pre-tension I assure you.

On a horizontal zip line the force at the terminal ends is 5X more than the weight.

So for instance 100kg in the middle puts around 500kg on the ends.

Pretension (1000lb I estimate minimum) + (5x 225lb bloke on it) ... I still estimate 2125lb minimum force on the system however you can dyno it to find out.

Of course as the line wont be horizontal the forces wont be maxed out however you need some spare up your sleeve. Rather than peen the rod over the nut use 2 nuts and lock them up. Use a heavy duty washer, do not etch out the bark.

The turnbuckle will have to be rated sufficiently to take the 2125lb+ force.

In your example the 1" threaded eye bolt will be taking force on the thread, you'll need to ensure the SWL of that is above the following.
Make sure all stuff is high quality and rated. A 1" dia eye bolt can have over 10,000lb SWL loaded on the thread no sweat, rigging eye bolts that size go over 13,000lb SWL in many cases.

At the other end what do you do eh?

I know, I consult for places that run these things. You got the expert right here mate.

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Go2Know

Thats good information. Thanks. I'll up grade my turnbuckle size.

I didnt understand your reply as to what to do on the second tree.

Sean Freeman

There are a number of different options as to the manner in which you could both securely attach the load line and protect the tree.

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Go2Know

Thanks Sean. Looks like just some type of tubing (garden hose?) over the cable for the walking and hanging lines. Stand off blocks of wood for the bridge on the other side of the tree.

To keep the 1/4" cable I'm using off of the tree in question I'd have to use 6 or 7 blocks. Each with two small lag bolts. So, which do you think is better for the tree. Cable or chain sling directly around the trunk with some protective tubing. Or, 12 to 14 lag bolts to hold the blocks?

Sean Freeman

My personal feeling is based on the inspections I've done on high ropes courses is that the blocks do less damage.

Some caveats though...
- none of the systems I have personally inspected are more than 2yrs old
- the blocks would need to have some groove cut into them if the load line were at an angle to avoid creep.
- the critical factor in my assessments was tree health and stability, whist I can and did apply my rigging experiences to inspecting the installations I was not required to make comment on the integrity of the hardware.

BTW the tubing is highdensity poly pipe whats called class 12 irrigation pipe here in Oz.

Go2Know

OK, sounds like blocks are the way to go. I take your point ab the groove being necessary to keep the cable from riding up. I think I'll just drill a hole through them all before mounting them to the tree. Then, feed the cable through. I imagine I'll want some kind of rot resistant hardwood for the blocks. There is a cypress sawmill down the road from me and they swear the stuff will last forever. Maybe redwood or cedar? How deep do you suppose I should lag them into the tree?

Sean Freeman

The blocks were 75mm (3 inches) thick and the lag bolts used on the trees I inspected were 125mm (5 inches) long.

The company that undertook the installations carries out annual inspections of all their hardware, the managers of the courses carry out daily inspections as part of their OH&S regs.

Go2Know

Sean, thanks for the input.

Eric Frei

Long term that system Sean shows is not as good.

It has more bolts, more things to go wrong and long term does more damage to the tree. The tree grows outwards in diameter around the stuff placed there, there's lots more growing around stuff than you'd have with one decent bolt in the middle. There's also no chance of girdling as the tree expands. How the tree grows is by cell division, when cells divide I assure you that they take the path of least resistance. So the new cells grows around stuff.

Properly installed stainless bolts wont rust or corrode, the tree grows and encapsulates it. We install packing to make the distance between the eye and the tree further apart so it takes time for the tree to grow that far. You dont really want the eye and cable getting encapsulated in the tree. Some of the systems I have worked on are now 10 years old, I have seen all methods age.

On the low end where you say the trunk is too large a diameter to drill right through, you need to adopt, a hybrid "bolt on eye plate/rigging plate". That gets bolted to the tree with lag bolts and the eye for your cable is in the plate. Thing is you have as many lags as you like. I have a recommended some where we use 2 or 3 3/4" x 8" lag bolts, I like to fabricate so we bolt vertically up and down to alleviate "trunk roll" as trunks are round.

So you can look for something like in the picture or fabricate your own via a proper engineer. All systems are backed up. You need to think that out so that if any terminating ends fail you have a back up, sure you might get a little bump as the slack takes up however it should be there.

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Go2Know

Ekka
I don't know a thing about trees and their properties. But, I do now just a little about rough carpentry. I HATE lag bolts. Your previous point about the force on the ends of the cable was well taken. The idea of that 2500 lb load being resisted solely by the threads of the lag bolts scares me. In construction I will tolerate lag bolts when I cant access the back of a structural member if they are supporting a shear load. 90 degrees from the axis of the bolt. But a pure axial load just doesn't sound like a good idea. Again, I know nothing about wood that's still alive. Tell me why I'm wrong.

Sean Freeman

I suppose it depends on the life span of the system...none of the rope(cable) systems I have inspected are intended to remain indefinately attached to the trees...it would be surprising if they were still there in 5yrs, I certainly doubt very much they will be there for 10yrs.

I personally doubt the impact of the blocks and bolts will be significant in that time, nor do I expect the trees growth to be dramatcally impacted.

Whether it is a system for your own kids or, like the ones I have inspected, a commercial venture, regular documented inspections of both the hardware and the trees is essential to proper management.

But Eric's idea is good too

Eric Frei

Lags have held trees together in the USA for decades.

The load is shared by more than 1 lag.

The system is backed up.

With the long term lags we have tried to inspect the heads sheared off before the thread turned. The through bolt has how much thread holding it? Usually about the same as the dia of the rod, so a 1" dia bolt will have about a 1" thick nut. With a lag you have 8" of thread in the tree. Pilot hole drill, coat with antagonistic fungi to prevent possibility of decay.

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Go2Know

Ekka

Where might I find that handy little ring and mounting bracket in your post?

Eric Frei

Search Google or see a rigging place.

Or manufacture one.

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rmckiern

Go2Know, I also live in the Tampa area. I've been wanting to setup a zip line for my 5 year old son. Be nice to see one in action to get some ideas. Any possibility we could look at your zip line setup?

Oldtimer

Go2know
I did a search on Google for "Zip Line Installation" and there are many responses with sites with photos of the equipment and places that sell the components. Some of them may be able to provide some advise for a small charge (I assume). Some others just post all the info right there for anyone to see and copy. (kind of problematic with liability - but - hey it its their site so...)

That may be a reason why many people here (and other Rec Sites I frequent) are not willing to offer specific instructions on how to do it for obvious reasons of liability. "Well so and so arborist told me to do it that way and it failed and someone got hurt........." Ouch.

Read a lot of the sites and get the best information from all the best sources and you will make the right decision.
One final problem with many of the accidents on these things is lack of "adult supervision" and regular inspections of the equipment.

If riders are going to be 20 feet up in the air wearing a safety saddle/harness and proper helmets is more important than anything else.
One suggestion: make sure the place is secured to public access when not supervised - Local kids have weir ways to get in trouble and fall from tall things regularly and get seriously injured sometimes for life. A good fall from 20 ft can easily break a person's spine or mess up their brain. I am not trying to scare you but after 8 years of Rec Tree Climbing I have seen how easy it is to have accidents by untrained users.

You can read the accident reports posted here and many other sites of people even "trained" people falling and injuring themselves.

Ok, I get off the soap box now

Eric Frei

Well, after much searching and travelling the globe via emails and cyberspace I got the low down on a pretty nice looking cable termination.

I like this, very clean and be a lot easier to tension the cable. Check out the smooth process to back up.

It all started with this news article (yes, I kept it to myself).
Zipping through the trees | through, trees, zipping - News - Santa Rosa Press Gazette

In the pictures of that news article (you can scroll 7 pics) I spotted this pic.



From that news article I tracked down the company and emailed them to ask what that cable termination was.

Got this email back

I then found the company that makes them.

And here is the link to that specific one they used.

Hubbell Power Systems - Products for Electric Utilities, Telecommunications and Construction Industries

But it did not have an Australian place to buy not did it have an SWL for the gear.

You can get them here from Britech in Australia.

Bri-Tech Australia

Now the SWL issue. So I emailed the manufacturer and was told ....

So there you go guys, some nice gear that termination is.

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Eric Frei

Evidence to prove what I am saying as correct.

I said earlier why I disliked that system Sean Freeman showed and here's the evidence.

These two pictures have a look at the uselessness of the polypipe, it's into the tree alright.





Now lets have a look at those platforms up the tree. They are bolted together with long threaded rod and just to make sure they don't slide down the tree they have half Koppers Logs butted underneath.

Note the damage at the log/tree interface. A lot more surface area than say 4" square thick packers (washers) which can be stacked out as the tree grows.









Now you'd think as the system ages and wears those half Koppers logs would crack and split, perhaps cables would pop out of the slots they are supposed to live in. Well all of that happens, and bolts with a head sticking out are used to keep the cable around them.

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Eric Frei

High definition video of a dissected Moreton Bay Fig after being through bolted 12 years ago.

Dissecting a through bolted Moreton Bay Fig

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sbe

Complete newbie here and usually I wouldn't post just after joining but I'm in the middle of deciding how to anchor the zip line I'm working on so this has been quite an enlightening thread.

One question. I'm not quite clear about how the packing works that spaces the eye out to allow for growth.

Great video btw. Am I correct that in this case the bolt wasn't spaced out and the diameter increased to well beyond the face of the anchor?

sbe

Of course 30 seconds after I post and it comes to me (I think).

Stack 4" square washers and remove them as the tree grows. Sound right?

Eric Frei

The thing is that once the tree starts to grow over things it will be hard to do anything if you think you can just loosen the nuts off at the back of the tree and the bolt slides so you can pack more washers. we have experimented with slitting a plastic hose and sliding that through the tree then the threaded rod, the hope is that as the tree grows the threaded rod can be pulled out but too early to tell yet.

However clever engineering on one of my sites allows us to pack out the hardware with the bolt/threaded rod encased in the tree. It's another thing we are trying.

How do we do that?

Think of the threaded rod in the tree as a bolt set in concrete, you cut it off after leaving some length spare. You bolt something to the threaded rod, if the tree grows to the point it's starting to get to the hardware you unbolt, and put more spacers in. See rough sketch. And yes we custom fabricated stuff.

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sbe

Got it. Seems like a good way to go. The only downside I'd suppose is that you have to keep on top of it since if one waits too long those spacers are going to be pretty well buried?

After reading your postings I decided to do a web search and came up with two interesting product, both out of Europe. Apparently there is a new standard over there that is intended to reduce stress for this kind of work. I haven't read it so I'm ignorant of the details but have found two product, both of which use straps that claim to be compliant and superior to drilling. Ever heard of Tree Save from Drayer (Drayer.de) or Cobra (cobranet.de)?

Both seem to operate on the same general principle. Cobra is a three part system (woven rope, insert inside where it goes around the tree and sheath) while Drayer seems to be a two part. Both claim an integrated, automatic system for upsizing as the tree grows.

As I said I'm an innocent when it comes to this sort of thing but I am an engineer and the idea looks intriguing. Plus the Germans really do seem to come up with some well designed stuff.

Any comments on how these might perform? Comparisons with your current methods?

Eric Frei

Are you zip lining or cabling a tree? Two different things mate.

We got all those docs here.

Tree Cabling| Bracing| Dynamic| Static

Rigguy Wirestop fasteners for cable

New Arborist Cabling Alignment Tubes

Also do some site searches.

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sbe

Zip line.

My idea was to use the straps around the tree and then transition to the cable. Drayer shows such an arrangement in their brochure though it isn't specifically intended for use with a zip line.

Your post makes me think I'm missing something important.