Zip line | zipline (recreational) attachment technique?

Eric Frei

Of course you are .... read the literature, digest it, think about it then get back to me with what the problem is using a dynamic cabling system for human transport zipline system.

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sbe

I read what you posted. Also re-read the Drayer literature and reviewed their engineering data and see two issues.

First, the product is not life safety rated.

Second, there is some debate regarding the loss of strength over time. I'm sure that has been characterized by now but it isn't part of their published specification at least not at this time.

Did I catch what you were referring to our should I put my thinking cap back on and keep looking for something more?

Eric Frei

You are thinking like an engineer not a tree man.

I think the Swedes did the same here in this day and age.

Will the Swedish Tree Hotels kill the trees?

The answer has been provided for you, check back with me that you got it.

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sbe

I'm trying, really I am.

Putting together the earlier information plus this latest article as best I can tell you don't like anything that bands the tree whether it be for support (the intended use for the product) or otherwise, such as a zip line. If that is your point I think I get it.

My assumption was otherwise. I was thinking you were saying these new products were fine for arbor work but not fine for my intended use. If that's the case then I'm still scratching my head because I'm not seeing that the load from the zip line is going to be any greater than in its intended use.

I have to either conclude 1) slings like this, even purpose designed as they are, damage the tree so should not be used or (perhaps less stridently) are a poor choice compared to drilling and bolting or 2) these slings are just dandy for arbor work but only arbor work.

If I believe the former then all these companies are wrong about their products. Not impossible but certainly not obvious.

If its that latter then I don't understand why. For example Drayer sells a 12 ton support swing. Again assuming it performs as represented that means the product will support over 40x the static load I would expect (5 x 200 pound passenger plus the cable length divided by two if I calculate about right). Even allowing for impulse loading that is no where near the limit of the sling. In fact its way beyond the load limit of the cable.

So I guess my question, if you wouldn't mind, is are you saying that slings like this are just plain a bad idea and shouldn't be used, that they are fine for the arbor work they were designed for but not a zip line or something else?

Like I said, I'm really trying to figure this out but it would help if I knew what your position was.

Thanks for your help. Much appreciated.

Eric Frei

Wrong on many counts.









My position is clear, pity you cannot get it.

I install dynamic cabling in trees and I install steel hardware to, I am not biased to either but each has it's place. I was hoping that all the data, pictures and discussion you could figure out when to use which and why.

Dynamic systems can also be installed for many years, the key is they are not tight or taut, they are loose fitted and allow for expansion.

You can buy them with shock absorbers or buy them with 5% or 20% stretch, but basically when installed they are loose and in such a fashion that the tree can grow. The idea is if the limb breaks/fails etc you catch it. So a 12T system isn't tension up. A simple rope over a tree branch just hanging there under it's own weight alone causes problems over time and I have seen tree limbs get strangled. These dynamic systems use wider sheaths to have less PSI pressure and try to make it easier for the tree to grow.

Ziplines are tensioned, and tensioned ziplines will magnify loads going across them. Did you know on a horizontal tension line (like a tight rope) that the force at the anchor point can be up to 5X the load. Working with long ziplines I asked the riggers for the kgs of pretension, they shoot for 500kg (1/2 tonne) then say the line is horizontal and you put a 100kg person in the middle you'll get around 1000kg of load each end (500 of pre-tension + (100kg x5)). So even a large wide leather strap say around half of the tree will result in trunk expansion issues on one side plus you have the fear that it could slide down the trunk. All the pictures in this thread show these things happening. The Swedish hotels are even worse.

Sometimes trees are steel cabled and bolted. We use static cabling (note the term because it doesn't allow movement and is rigid) when the defect is such that we do not want movement. It could be a fork in the tree that has already cracked and we are pulling it together, bolting and cabling.

Dynamic cabling systems should be perhaps referred to as fall arrest systems, they catch the limb if it breaks. Also twin trunked trees can be dynamically cabled to prevent them splitting rather than rigid bolting. There is some debate from polarised view points but there could be some issues, like Yanks do not like dynamic systems, say critters (squirrels etc) chew through the rope so they like steel cable.

I use the right application for the right reasons.... and do not run around saying drilling trees will disease or kill them. I see more often the opposite (strangled/girdled trees).

This simple bit of 8mm rope from a disused swing wasn't removed, almost killed the limb.



In this picture you can see the tree is half dead. It was ziplined over a branch so it didn't slide down and around the trunk with chain. I t wasn't very tight as the two trees it was between were on a hill so both trees were tied at about the same height (horizontal zipline now) but the slope of the land gave the downhill run, the sag in the cable is what prevented kids smashing into the other tree, they bottomed out.





If the installation is permanent (there for good and not just the weekend) and has to be solid, not slip and slide, then bolt with spacers so the tree can grow for years.

I hope you get it now.

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sbe

I do.

FYI I also see we aren't talking about the same setup for a zip line. Look at each of our calculations for pretensioning. You're assume the line is straight while I'm not.

Zip lines can actually be set up two different ways. The first way is to pretension the line to make it straight. This is the way most commercial lines work. Residential lines and those where the rider will ride using a seat rather than a harness are different. These are generally set up with substantial slack.

There are a couple of reasons for this. First is safety. A slack line is designed to have a run up at the end so the rider slows down without the need for slowing themself (this is a requirement if one isn't using a harness since there is no way to reach up and grab the cable). It also makes unloading safer because it happens at ground level. Finally (as you noted) it reduces the cable loading which makes installation easier and safer.

This is why we came up with such different numbers for loading (you 1000kg, me 275 Kg).

What I hear you saying is it don't make no difference stupid. Even the lower static load spread over the surface of a 12 ton sling is too much. But a 330' run of 3/8" cable weighs about 81 pounds. A zip line is designed to drop 6% or about 20' for a 330' run. Designing for a sag of 20' (40' total drop to bottom of loop) results in a pretension of about 180#. So the total static load on the cable when not in use (99% of the time even assuming heavy use) is under 300#.

Is 150# per end static load spread over the surface area of a 12 ton sling is enough to avoid damage? That is a static load of less than 1% of rated.

You have said these kinds of systems are installed loose. But does loose mean the guy lines have zero tension at all? I think you are saying yes and I'm only asking again because the pictures seem to indicate this isn't always the case if for no other reason that some amount is sometimes necessary to keep the sling in place.

sbe

Since I failed to say so explicitly thank you again for your help and in addition being so patient with me when I fail to reach the correct conclusions on my own.

Eric Frei

Usually the slings are installed above a branch union or somewhere so it doesn't slide. If pretension is required to keep the sling in place then I wouldn't approve of that.

We install our dynamic cables loose, no tension at all.

Of course these systems need to be monitored as growth could go around the obstacle rather than push it out.

There is another factor I worry about, that is the dampness issue between the sling and the tree,can become a decay point.

Knowing this why would you sling a permanent zipline?

These bird boxes have a wire that is zigzagged so as the tree grows the wire is opened up and the box plus wire move out. Now this is a relatively new installation but I already have my doubts. Time will tell but I think the tree might encase the wire, not sure what will happen where the box is in contact with the tree either. The alternative would have been for the boxes to be screwed into the tree with a tube or packing washer between it and the tree allowing room for growth, would have been permanent, sturdy etc.

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sbe

I'm convinced. Rather than risk damaging the trees we'll sink a couple of telephone poles and hook the ends of the zip line to those.

But because I don't relish the idea of having to move the poles if I get the design wrong I'm going to buy a couple of the 12 ton slings and use them around the trees to mock the system up and test it. Once the slope is set then I'll just move the line over to the poles.

Again I'd like to thank you for your assistance. You helped a lot and I hope your efforts to convince people about the damage they inflict with the traditional method of cabling, especially zip lines, has an effect. I'll make an effort to pass the word along to the community up here in the Northwest (USA that is).

Eric Frei

I just dropped a post into this thread I had hidden elsewhere.

Want to see a fantastic cable termination and back up (yes, always back up) for zipline? Of course you do with data.

And this guy appears smarter than the Swede's:

Treehouse Engineering - Charles Greenwood PE. Recognized authority on the Engineering Analysis of Treehouses.

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sbe

That Hubbell part really is slick. I've used Hubbell stuff in my work and I've found it to be top notch. Thanks so much for that. Did you end up buying some?

The tree guys are just a couple of hours south of me so I'll have to give a call and drop by on my next trip south (us Oregonians are real friendly). That is some very slick hardware they have going.

Again much appreciated.

BTW cool web site. I've learned a lot although not the minimum number of runs to score a century in cricket.

Eric Frei

Haven't used one yet however recommended them. Most use eye bolts with washers.

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Jeff Darby

wow, all that effort and just thanks? I thought it was customary to tip in US of A ? sapsuckers suck the goodness out of trees, Treeworld is a big Tree helping many for very little it would seem...

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© Jeffrey J Darby 2011

Jeff Darby

I must say I am flattered by your donation, and confused as Eric made the effort... I only made a comment

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Join the Australian Tree Association...Have your voice heard !

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Eric Frei

Interesting.

I never got a cracker, nothing. You give him a hard time and get a tip. Most interesting.

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sbe

Oops.

You have to understand sites don't work like this in the US. Our custom doesn't include money. Somebody helps me, I help the next guy (or somebody on another forum) and there isn't a mechanism to give somebody money even if you wanted to. So I wasn't focused on that being the way things are and then when informed it was I read carefully enough to see pressing the link wouldn't mean the person who helped got the donation.

Sorry about confusing everyone. I was just moving too fast and not paying attention.

Jeff are you willing to forward Eric the money since that was what I intended?

Jeff Darby

Not a problem... as soon as it shows in my paypal as I only have the email from paypal @ the moment, I will forward it on... On a further note the amount of information stored in the threads of Treeworld are valuable and free for every one to access, its just nice to see some appreciation every once and a while. Thank you for showing you understand the value of thousands of hours of unpaid work to keep this forum up to date for the public domain...

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Join the Australian Tree Association...Have your voice heard !

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Eric Frei

It is not only the upkeep of the forum, the hosting but also the helping.

The industry itself can be extremely biased and imbalanced. Opinions often come with little fact, research and data. I mean on this topic you'll see tree huggers scream that you are wounding the tree by drilling, that it will die etc.

So not only do I put the information out there I have to constantly justify it, unlike the provocateurs who just rant on and work in MOBS usually. Then you have to convince others as their heads are full of BS from elsewhere. Often I think to myself, "ah let the dumb asses not know, do not throw your pearls to swine, they are not worthy".

Look around, how many arborists are putting solid information out into the public domain? Stuff all, and a lot of it can be very biased to their personal agenda.

You look at reward or return, is it worth it? Well, 5 years I have been at it, and when it comes to putting your money where your mouth is sadly most people run away, with the information, now updated with knowledge and do not part with 1 cent .... sap suckers that can kill services like this.

Everyone loves wikipedia, anyone donate or add content to it lately?

Here's what the owner says:-

I do recall days where they near on begged for money and they were on a thin line. People treat the web totally different to how they treat people, but behind every post here is a person, do not forget that.

Without funding, nothing runs. We have minimal advertising, no Google ads everywhere and keep the place running for the benefit of the industry.

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sbe

I think you just have to do it because you enjoy it is all.

I'm a very frequent contributor to a site up here for frequent flyers. The airlines make a habit of really screwing people who try to cash in their points sometimes, in particular when a flight is cancelled. They tell people they can't go, even when there are seats, if they've used FF miles to pay for the ticket.

Well it just bugs the hell out of me that they pull this trick. They know their own rules require them to treat passengers who pay with miles and those who pay with cash identically, but they don't do it because they want the seats back.

Anyway almost every month there is another posting by some poor guy who has his whole vacation set and a day/week/month before the airline tells him "tough luck." So I spend a couple of hours researching the tariff for that particular airline, quote the appropriate section, post it then deal with the same storm from no-nothings who think they know the answer but have never bothered to even read the tariff let alone understand the governing law.

Why do I do it? Ego? Or some satisfaction knowing I've saved a guys holiday? Both probably. But it comes around because when I need to ask a question there are always a couple of guys out there who know and it saves my rear end.

So what goes around comes around. I help with frequent flyers, you guys help with trees. Maybe you'll need some help with something at some point and there will be a forum and somebody knowledgeable who takes the time to post a reply. I hope so.

In the meantime thanks to you for your help. I've emailed a copy of the data sheet for the Hubbell part to the guys south of here (near the tree house guys) who do a lot of zip line stuff and they were pretty excited. I'm going to point them to this thread and see if we can save a few trees.

Eric Frei

This rope was put between two trees, it hangs loose and it was used as a clothes line.

On one end it was tied with know that was tight around the tree, a cheese tree about 8" diameter where it was tied.

The other end was slip knotted to a weed species chinese elm branch maybe 4" diameter.

The interesting parts is that the line was only there for 1 year, what you see is 1 year worth.

This is the tight end with rope there



And with the rope gone



This si the loose end, note the gap between the rope and the tree where the know could not slip any more due to splice/crimp.



And with the rope off



Now clearly this alone should be ringing the bells.

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