So what have I been up to in the last few months?  Thanks to a reader with access to a plasma cutter, I was able to cut a batch of 4130 steel plates.  The upside of 4130 is that it’s about twice as strong as 6061-T6 aluminum; downside is it’s also three times as heavy.   So the steel Kofi is a hair over 1000 grams, compared to the 500 grams of the aluminum version.  The side plates are actually thinner than aluminum (.19″ versus .25″), which saves some weight, and I grew the dimensions marginally to add a bit more internal clearance for fatter webbings/hardware as well as a bit of meat to increase break strength (which is now theoretically around 20,000lbs).  As you can see in the image linked above, plus in the images below, the steel plates have a hand finished look (since they were roughed out using a plasma cutter), but they should work just fine for my needs despite each Kofi having a “one of a kind” hand build. I am working on sourcing bolts that are the exact correct unthreaded-shaft-length, so for now washers are necessary to get the spacing right.

What’s on the agenda for the rest of this “work in progress” article?  Testing!

Holding power.  Lately there has been a lot of debate in the community about the holding power of adjustable webbing anchors.  My experience (written about in the first article) has been that any “gap” to the sides of the webbing drastically reduces the holding power, at least for more slippery webbings.  (Basically, I would not trust polyester webbings beyond 5000lbs without some other precautions taken.)  Others (from Landcruising) have said their tests show this gap makes no difference.  Backing up their point of view, Jerry at Balance Community has released the new AWL (“3.0″) with its roller and one sideplate machined as a single piece.  That the roller itself cannot “roll” (because it is part of the sideplate) means, Jerry claims, that the webbing, even slippery webbing, will break before it slips.  Effectively he is saying that webbing slippage that led to creation of devices like the Monster Lock is from the roller itself turning under load.  Although it would make sense that the roller, if it turned, could cause slipping, that it doesn’t jive with my intuition about how well locked in place the roller is or about the torques the roller experiences.

I can do some physics on paper to make my point, but there is so much going on here that actual testing is a much more valid approach.  Before that, however, let’s talk just about about friction and why wrapping material around a pole will keep it from slipping.  You probably already have a reasonably intuitive understanding of how friction works.  For instance, if you have some tension on a rope and you’re going to tie it around a pole, if you wrap the rope several times around the pole and THEN tie it off your knot will be more likely to hold.  This is because of the friction involved (and in the next paragraph we’ll dissect that a bit).  However, there are also some pretty nonintuitive things that happen regarding friction.  For a good explanation of this, since I am not a physicist, listen to a couple minutes from MIT’s always-entertaining Walter Lewin (an actual physicist!).  So what makes adjustable webbing anchors so special is the contact angle that takes place when the material is wrapping around the roller and pin.  It’s this wrapping that so greatly boosts the holding power.

We know that webbings in the “double wrap” method do not slip, but in the single wrap they do.  I have sketched a quick document that explains some of the physics involved when a rope wraps around a pole (which, on a basic level, is sort of what is happening with an adjustable webbing anchor, plus there are some complications on top of that).  With some basic (but possibly wildly inaccurate) assumptions about friction of webbing on metal (and neglecting webbing on webbing friction) you can see that a piece of webbing wrapped around a pole (perhaps nonintuitively the diameter of this pole does not affect the calculations) a “single wrap” will hold about 50x the weight of the tail before slipping, versus around 3000x for the contact that takes place in the “double wrap.” But of course the double wrap isn’t adustable, specifically because there is so much friction at play.  So the benefit of the single wrap is that if you lift the slackline a bit (so it isn’t pressing down on the front pin) and pull on the tail, you can feed slack into the device.  Once you let go of the main line and it is pressing down on the front pin again the physics of the situation have changed such that slippage is now seemingly impossible.  So the question is, at a very high tension, when slipping does occur, why is this?  It could be the webbing can pop out from under itself, it can be the roller can turn, or it can just be that there is nothing “holding” the tail except its own weight and as my sketching above shows, at some point the tension is enough to overcome inbuilt friction (so for more slippery webbings this is an issue).

Basically what I intend to do in the near future is a series of video tests that will be posted here where I pull the same piece of webbing to a given tension to see if it slips.  I plan to test:

1. Kofi with huge gap between webbing and side plates (I will use a 1.25″ roller)
2. Kofi with no gap but center roller is loose and maybe even “greased” on the sides (where it touches the plates) so it will roll easily
3. Kofi with standard center roller and also a front bolt rather than a pin

Break strength.  It’s time to test the calculations of the Kofi.  With both aluminum and steel versions it would be nice to have a final answer as to how strong they are.  I have gone through enough design iterations that it can be hard to remember which version I settled on for the many random prototypes kicking around my apartment, since I keep tweaking the break strength (from 10,000 to 14,000 to 20,000) and I’d like to have a concrete number just to allay my fears that theory doesn’t always translate to practice.  As long as the break strength ends up being over 10,000 for all devices then I will happy since there are several other components in a rigging system with lower strength (including the webbing in almost all cases).

Teardrop rings.  These suckers are often hard to source in American-made brands and the one readily available source seems to be Chinese.  This may not be a problem. Or it may.  I’m going to break some, and then we’ll know.  They are rated for 1800lbs working load and so far I have only consistently tested them to about 1500lbs (with no issues).  I’d like to see them get much closer to the 8000lbs mark before breaking (at which point I would consider them safe).

This article, for most readers, is meant to just be a bit of a curiosity. I am not encouraging you to build your own webbing anchor device. Why not? Well, unless you have access to: machining equipment; a qualified engineer who can double check that your materials and tolerances are safe for the loads the device will be subject to; and the capacity to test the device in a controlled/isolated environment (with a dynamometer) in several configurations before it actually gets used, I just don’t think it’s a good idea. There is a lot of work that goes into designing and building these things, and the devices offered by Balance Community and Landcruising are well-respected and well-tested — plus, they put in a lot of work and deserve to be compensated for that. So this article is meant to be simply informative to most people, and for the few of us who do have access to machining equipment, friends who are engineers, dynamometers, and a lot of extra time, it’s meant to establish a base level of knowledge about the state of webbing anchors. It will, hopefully, be a document in flux.

What I think a webbing anchor should do, and why I decided to build one

I wasn’t exactly thrilled with anything on the market. I already owned two slack bananas, and they worked great, but they were no longer made. I was actually a pretty big fan of the look and size of the AWL 1.0, but it also is no longer made. So, I decided to make my own webbing anchor device, incorporating various aspects that seemed desirable to me. The idea of NWslackline is to build community and advance the knowledge of slackliners everywhere. For this reason, I decided not only to build my own anchors, but to do so in a very public fashion, so that others (see above!) may improve upon my ideas. The following is a general guide to my design process.

Disclaimer! Longlining is inherently dangerous, and for this reason I must insist that you do not consider this a guide to building your own anchor by yourself. Consult a qualified professional engineer before you build and rig with any prototype devices.

So what should a webbing anchor do?

1. Be bomber. 10,000lb / 44kn break strength or better.
2. Be lightweight. Although we may use this to rig 1000-foot lines, it should feel at home on a 30′ line.
3. Be small. See number two.
4. Work well with a variety of webbing materials (nylon, polyester, ‘high tech’ webbings).
5. Be quick and easy to use.

One thing I do know, by looking at what is publicly out there about the evolution of devices on the market, is that pin/bolt orientation is somewhat important. If pins are too small or too close together, the outer fibers (as they wrap around the pin) are required to stretch/warp too much, and they snap. Jerry at Balance Community explains these fiber issues well in his Slack Science blog. If the pins are too far apart, not enough friction may be generated and the webbing may slip far before its breaking strength. I seem to recall (but cannot find a link to) tests by Terry (“still-slackin-thru”) of the original banana which showed that Type18 slipped around 5500lbs, whereas in a shackle-locker (essentially no possibility of slip) it broke at 7200lbs. Lastly, to generate optimal friction, the orientation of the back, middle, and front pin is critical, so that under tension the webbing is pressing “down” on the loop that is captive in the front pin. There is at least one device on the market where manufacturer marketing pictures indicate that the line is not “pressing down on” the front webbing loop (from my perspective, anyway).

The design and build process

I mocked up a banana-type design similar to Michi’s 2009 model and traced it onto some scrap 1/8″ wood. I then modified the hole spacing, and found that everything seemed to fit properly still with the holes closer together by about 1/2″. Simultaneously, I had a big rectangle (slacktangle?) webbing anchor (6×3″!) CNC machined out of 0.25″ T6 aluminum to these specs. The goal was to test the properties of this device starting with small modifications on a known working idea and move forward. A friend of mine has been rigging on this slacktangle for several months now with no issues (other than the fact that it looks ridiculous and is bulky as heck).

Next, I laid out a “kidney bean” webbing anchor in Adobe Illustrator and consulted with a friend who is a licensed structural engineer. He verified my calculations, that the device (two plates of .25″ T6) would have a 50Kn break strength (11,250lbs). I first laser cut this out of acrylic to check webbing fitment, and after verifying the fitment seemed good, moved on to CNC machining a prototype. I elected to use .5″ grade 8 bolts, not because we need bolts this strong, but because overkill is something I believe in, and additionally .5″ is a very common size and makes finding commodity hardware easier. The double sheer strength of the bolts exceeds the strength of the plates they are going through. If we want stronger plates later on, we can change thickness or material type, and because the hole spacing and size won’t change, everything else (the function of the device) should remain the same.

Almost every webbing anchor uses spacers/rollers, mostly to increase the diameter of the webbing loops. I settled on a 1″ center roller and .75″ outer spacers for testing. This is very close to what the original BC-edition banana used. The spacers can be swapped out to longer versions (along with longer bolts) for the ability to rig 1.25″ (32mm) or 2″ (50mm) wide lines, such as RAGEline or the Gibbon SurfLine. Some (most?) webbing anchors also use spacers as a way to protect the webbing from the threads of the bolts, as well. With my design this isn’t necessary, as we have special bolts that are unthreaded for the length of bolt within the device — this means the bolt is extra strong where it is being stressed within the device, and there is no chance the threads can contact webbing or can damage the aluminum sideplates or spacers/rollers.

The front pin, where the main loop of webbing reverses on itself, can be a bolt and nut (for ultimate security) or a super-strong quick-release pin (1000+lb pullout force) for quick setup (the downside to these pins is they often cost more than $40 each!). Initially I believed a .75″ front spacer around this pin/bolt was necessary, but many tests on various webbings have shown that the majority of stronger webbings will hold 5000+lbs using just the .5″ front bolt/pin with no spacer (one type of poly webbing slipped an inch or two in the high 4000lb range).

The rear bolt allows for a variety of rigging configurations. Either two bomber forged 3″ rings (88Kn), two 2″ forged aluminum rings (64kn), two 4″ dyneema loops (44Kn), a standard 6″ tubular nylon loop (32Kn), double carabiners, double 3/8″ teardrop rings, or a single 3″ ring with a special tapered bolt spacer to keep everything centered — any of these setups can mate to a shackle, quick link, carabiner, or directly to a sling. I wanted to design a device that could mate to a shackle and offer 20,000+lb strength (with the right configuration and 7075 sideplates) for highlines and super-longlines, but also be super lightweight and go right on a homemade sling (no shackle required) for folks who want to travel light and only need 6,000 – 10,000lb break strength.

For now, here is the device at a glance:

What webbings will a Kofi work with?

The default setup will work with any 1″ webbing (24-26mm). Because polyester and super strong ‘high tech’ webbings (such as Spider Silk) are known to slip at high tensions, it is suggested that with webbings of these materials, an alternate (“double wrap” or “wrap and a half”) method (or tail securement) is used. The secondary (.75″ diameter) spacer should probably be used with “high tech” webbings — our testing will soon show whether it is necessary or if it helps avoid slippage at all. If you want to rig 1.25″ or 2″ wide webbing, or even half-inch webbing, this is entirely possible with a different spacer/bolt set.  I have rigged all of the above webbing widths using the Kofi.

What rear-bolt connector options are there (to connect the Kofi to a spanset/sling)?

I already ran over it a bit above, but the basic premise is you can go down one of two roads: either a fabric sling, or a metal connector.  Fabric slings should probably connect to metal hardware (e.g. a shackle) rather than more fabric (e.g. spanset).  I have not yet tried putting thick rubber hose over a spanset, but others have had success with this for shortline rigging (to my knowledge it is untested for high-tension rigging). I have a friend who is using the dyneema slings directly on a spanset, but I don’t recommend it.

Fabric connectors:

• Dyneema 8mm slings (22kn each x2)
• Nylon 1″ slings (32kn x1)

Metal connectors:

• single or double 3″ steel ring (1/2″ metal stock)
• single or double 3″ teardrop ring (1/2″ metal stock)
• single or double2.5″ steel ring (1/2″ metal stock)
• single or double 2.25″ teardrop ring (3/8″ metal stock)
• doubled 2″ aluminum ring (1/2″ metal stock)
• doubled carabiners or quicklinks (not advised)

This is the part of the article that could really be expanded to be its own individual article.  I have tried a LOT of different rigging methods, and I love that the Kofi will accommodate basically anything I want to do.  Modularity is good, and I love tweaking rigging to get everything aesthetically perfect.  I started using fabric connectors, and here I would favor doubled 8mm dyneema slings (for redundancy).  With the 44kn break strength they are definitely up to the task.  That said, they could “somehow” maybe be cut, so I started to favor metal hardware.  The 3″ rings are preferable because they are insanely bomber.  But, they are fricking HUGE.  They dwarf the device as far as size goes, so unless you need to pass a few spansets I don’t think they are optimal.

Next I started to favor doubled 2″ rings.  They are light (forged alum), small, and strong (32kn each!).  Because of the amount of “meat” that the Kofi has around each bolt hole (more than 1/2″ of material) this means that a 2″ inner diameter ring (which are actually not quite 2″ in my experience) will not have more than 5/8″ of space left to pass a spanset/sling through.  For a nylon sling, or a purple spanset, this will be fine.  For a green spanset, it won’t.

Next, knowing I wanted a metal connector that was small, strong, and allowed for a large enough opening to comfortably pass a green spanset, I started working with teardrop shaped rings.  My basic thinking was that I wanted more lateral space with the same vertical space, and this would mean a non-circular connector.  The cool thing about the teardrop shape is that it is actually stronger in the loading direction than a totally circular ring (which is equally strong in all directions).  So the 2.5″ ID teardrops can have a MBS of 15,000+lbs, compared to the 10,000lbs of a 1/2″ barstock circular ring.  And the 3″ ID teardrops go as high as 42,000lbs (again, compared to ~10,000 for the typical 3″ ID circular ring).  The teardrops are therefore safe to use by themselves, or in double.  And two will easily fit.  I generally double them.  The cost on them varies, depending on maker, but they can be cheaper than an equivalent sized circular ring.  Color can denote either strength or manufacturer (so you need to be pretty familiar to know what each color means), so rather than using up any more space, let’s just say everything pictured has a break strength exceeding 10,000lbs-per-teardrop.  Best of all, even the 2.5″ ID version (i.e. the smaller ones) easily pass purple spansets as well as green!

So now the question becomes “to double or not?”  Doubling costs twice as much for the hardware, but it allows you redundancy, and it keeps the Kofi more stable under weird loads (surfing, etc), which means everything stays straighter.  Plus the extra surface area means less stress on your spanset/sling.  Also, if you don’t double, then you need to come up with some hardware method to keep your ring/connector centered, and that might be just as expensive as the extra connector.  So let’s talk about the cons/options of each method.

Doubling on thinner hardware (or just-slightly-less-than-half-inch hardware such as the aluminum rings) is straight forward.  You just put the connectors on there and you’re done.  Basically there will be 1/16″ or less of “play” to the side of each connector, so everything will sit pretty straight.  I have taken to adding a washer on each side if I want to make sure it all sits absolutely perfectly, but this is not necessary (I am just anal).  Doubling on 1/2″ thick hardware is more difficult.  The 1/2″ hardware tends to be just over 1/2″ (the 3″ rings that BC sells are a miniscule amount over 1/2″) and so you cannot fit two of them in a 1″ space.  I do have some 3″ rings that are truly 1/2″ and so they fit doubled up, but the source I had for the rings is no longer in business.  Sanding/grinding rings down is a bad idea because of microfracturing etc, so one would proceed there at great risk.  A way I got around this was to create a special spacer that would widen the device while “taking up space” for the front two holes and not the rear anchor hole.  This means the webbing still fits tight, but the device is now 1 & 1/16″ wide in the rear hole (allowing for double 1/2″ rings).  Because the smaller teardrop rings are so strong, and because they work “off the shelf” I have only made two of the aforementioned widening spacers (because they are a pain to make and doubled 1/2″ thick rings are overkill).  If I needed to pass three or more green spansets, I would probably use this special spacer method, though.  But I would only need to do that for some crazy type of highline rigging.

Single connector means everything will fit, but you need to keep it centered.  There are two ways to do this.  One is with a centering tube.  This is basically a smaller “roller” that is grinded so anything that sits on it will naturally slide to the center.  Landcruising’s solution is so pretty I just have to link to it.  So I could do this via notching, or by making it into a sort of hourglass shape.  I elected to do the second because it seemed more elegant.  I did it by hand using a lathing method (and sandpaper), and it wasn’t super quick, nor super cheap.  Including renting lathe time, each spacer (I made 4) cost me about $10 (still cheaper than $16/ea for the ZenTube, but mine are not as pretty, and $10 is too much!).  Eventually I decided to try washers instead, and found some varying thickness washers that fit perfectly and cost less than $.15/each.  This means 5/8″ wide worth of washers is about $1.  This is my new go-to method for filling space in the “hardware connector area.”  For a different angle on the scene in the photo at left, click here.

What is the absolute best method?  I guess it depends on your perspective.  There might be something even “better” I just haven’t thought of yet.  And of course, I haven’t directly connected a shackle to the Kofi yet.  That, for some reason, doesn’t appeal much to me, although it’s definitely a bomber way to go if done right.  For now, I think doubled teardrops is the method of choice, but dyneema slings, doubled aluminum rings, basically all of the other methods are adequate for many if not most situations.

Random important lessons I have learned.

• Roller width is critical. At first I wanted to overshoot this a bit, so the webbing would pull through the device a bit easier. So we went with 1.1″ instead of 1.0″. In pull-tests I found that polyester webbing can actually “slip out from underneath itself” using this extra margin. It would pop out around 4500-5000 lbs or so, and then a fraction of a second later “slip back under itself” and catch the remaining tension (maybe 3000lbs) melting the webbing to itself in the process (see image at right).  Although 4500lbs is well beyond the safe working limit of both this webbing and the Kofi, the slipping and melting is still not ideal. Changing the roller width down to 1.0″ appears to eliminate this (this same webbing now holds 5,000+lbs (with a rated break strength of 6600).

• Rubber printed and resin impregnated webbings pull through the Kofi very poorly. This is nothing new, I think they do this on all devices. They just have more friction. In general the thicker, stiffer, and stickier the webbing the harder it will be to pull slack through. Tubular nylon is a DREAM to pull through the Kofi.  The more compact the device, the more difficult the pullthrough will be as well.  Also, you should never load rubber printed webbings upside down.  The rubber print should always be facing up (or “out” if for some reason you were rigging the Kofi upsidedown) — this is true, I believe, of all banana devices.  (I loaded the rubber print facing “in” just one time and it was not good.  I actually can’t remember the details of what happened, I think the extra friction melted the rubber maybe, but whatever happened I made a permanent mental note never to rig this way again.)

• Bolt spacing is also key. Perhaps if the bolts were further apart the webbing would also pull through easier, but I reason this would allow it to slip easier. My goal was to make the device as tiny as possible while still allowing for various webbings to be used. Tubular nylon is very thin. Webbings like Mantra, Gibbon ProLine, and Type-18 are much “thicker” and require more space. In general you need to think about the thickness of 2 or even 4 layers of the webbing (depending on how you plan to wrap) in order to know the minimum hole distance. Also, if the device is symmetrical (like the Kofi is), that means the rigging bolt (rear bolt) can have a space impingement issue with the webbing too. Devices like the AWL/Lynx/etc avoid this by moving the webbing bolts (front and middle bolt) forward and leaving a bigger gap between the middle and rear bolt. The minimum distance between the inner edge of the rear bolt and the rear edge of the middle bolt should be 32mm (in my opinion). (This last dictum assumes a 1″ roller — the bigger the roller the more you will need to increase this distance.)

• Roller size. I think there is some benefit to a 32mm roller, or even a 40 or 50mm roller. However, from what I do know of break test numbers that commercial webbing anchor manufacturers have generated while designing their products (and shared with me later) it seems like somewhere around the .75″ – 1″ mark you gain 10% in break strength improvement for every 30-50% of roller diameter you increase. So a 40mm roller might offer a 10% reduction in the difference from “rated strength of the line” and “actual break strength in the device” when compared to a 25mm roller, but this improvement is probably only a 10-20% reduction (of what might be less than 5% under rated strength) despite a near doubling in roller size. For my uses, I am balancing the size/weight/cost of the device against the ability to turn in the best possible technical performance. I feel like 25-32mm is the sweet spot for that. I have further testing planned to verify this (see below).  Basically a roller should never be below .75″ in diameter, and I really feel like 1″ should probably be the minimum.  If you use a .5″ or .75″ roller with static webbings, you’re going to have a very low break strength.

• Bolt threading. As I said before, having threads inside the device is not a good idea. This necessitates protective spacers in a place you might not want to use them, weakens the bolts’ performance in sheer strength, and if the device is aluminum it will likely blemish the device or even distort the bolt holes at high enough tensions. Sourcing the right bolts is difficult, but worth it (to me). Shoulder screws are another option, but again still would have threads inside the bolt holes on at least one side plate. The way I’ve done it, the device is as strong as possible, and any bolt can be substituted for a quickpin whenever desired.

• (50mm) 2″ Webbing. I have heard through the grapevine that others have had issues with 2″ webbing in their devices, and it would stand to reason that 2″ webbing must present SOME problems, since there aren’t a lot of 2″ webbing anchor options on the market. Or perhaps the demand for these devices is just too small. To address some rumors I have heard: what I do know is that in my testing, 2″ webbing holds 5000lbs of tension without slipping. I have also heard that the tension needed to trickline will bend the bolts. This, so far, has not been my experience (and my gut would say they shouldn’t bend, since the tensile strength is well over 20,000lbs, the single sheer load at threading should be around 13,000lbs, and the double sheer load of the non-threaded portion will be in excess of 26,000lbs … given that grade 8 bolts are tempered to NOT bend, I am skeptical of bending). You can calculate tensile by taking the tensile stress area of the bolt, multiplying it by the PSI tensile strength of its grade (150,000psi for grade 8), and then single sheer is generally 60%+ of tensile.

• Steel versus aluminum. T6-6061 aluminum has a tensile strength of around 45,000psi. It’s important to make sure you are getting T6, as there are other (much lower) 6061 grades. T6-7075 has a tensile strength of around 83,000psi (nearly double). It weighs just slightly more (within a margin of error as far as I am concerned). Price is roughly 2.5x the cost of 6061-T6, however. T6 is the heat/temper designation. 4130 steel has a tensile strength of 81,000psi, but weighs nearly 3x as much as aluminum, and (through my metal sources at least) has around double the cost of 6061. Steel is also much harder and so more difficult to machine for certain processes (say if you were making these yourself using hobbyist tools). The upside of the hardness is that your device will still look pretty much new even after you drop it several times and toss it into the gearbag month and after month. The devices in the pics above (with the tear drop rings) are some of the first ones I ever built, having been used for nearly a year now (thrown many dozens of times into a gearbag with steel shackles and pulleys and so on) and if you look closely they have little blemishes that reveal this. The aluminum devices will show some small scratches and maybe even a tiny ding or two if they are banging against steel hardware. For me, aluminum makes the most sense as it is strong (or REALLY strong), lightweight, pretty inexpensive, and easy to work with. The added strength of steel is appealing, but the weight puts me off. My next run will be either steel or 7075-T6, I am unsure which.

• Bevel the edges. I haven’t had any issues with the inner edges of the device cutting webbing, but if the sling is loaded a little weird and the device gets kind of crooked (more likely to happen if using a single attachment point to the sling instead of doubled rings or whatever), the webbing might touch the inner edge while under tension. Right away I realized this needs to be beveled. Rounding it with a file and sandpaper, or just using a grinder to put a 45-degree bevel both seem to work fine. Another upside of aluminum over steel is these little changes are easier to make after the fact using hand-tools. The nicest option is to CNC the entire plate from a thicker piece of aluminum, like Landcruising does, so you can machine the bevel directly onto the hardware at the same time.  BalanceCommunity also recently announced their updated AWL (“3.0″) that also is CNC finished.

Things I wanted to do before publishing this article but have decided to update later

Break tests of the following webbings:

• Tubular nylon
• Type-18
• Mantra
• Spider Silk
• Gibbon ProLine

I have recently acquired a 50,000lb dyno to do the above testing, and when I have time and good weather will try to get it done.

• Slack really, really hard several times on a 50′ piece of 2″ webbing and verify that bolts do not bend.  During summer (Aug, 2012) I got the final bolts and quickpins in to do this and put in a few sessions with no apparently issues. I need to do several more.

• Break testing of a low-strength polyester webbing with a variety of roller diameters (13mm, 19mm, 25mm, 32mm) and data analysis to determine how roller size affects break strength. I acquired a low strength (2000lb) poly webbing and roller materials to do this, but have decided my experimental design had flaws.  I made this decision after getting a baseline using a 25mm roller, and it broke right at rated strength on that roller (something like 1975lbs).  The problem with the webbing I acquired is that it’s very thin.  I am still working on an experimental design that will be reasonably useful for a variety of typical highline webbings but doesn’t require me to spend to get access to a commercial wire rope testing facility.

Design updates?

I have been thinking a lot about the next generation of Kofi type device.  The Kofi works great, but it’s also a sort of derivative/hybrid of what is already out there.  It has some limitations that I would be interested in coming up with a novel design (something totally new) to address.  I am working on a new design that will be steel and more compact.  It will weigh a lot more, so I wouldn’t use it on a day to day basis.  But it will have a break strength of around 50,000+ lbs (175+kN) so it would be useful for very long highline and other applications where insane strength is valued over everything else.

Questions?

I am publishing this ahead of time since it’s been a “draft” that has been visible only to me for a good 10 months now and I am getting sick of revising it with only me able to see it (and people writing to me in private to ask many of the questions that are answered above). Feel free to e-mail me if you have questions/thoughts, want some help, or want to offer some help.

Rather than re-write everything that’s in the video, I will mostly let it stand for itself.  Instead, I’d like to use this space to give my recommendations on what you should buy for your first longline setup.  We will consider three price levels.

The “broke college student” longline setup:

• Two CAMP or Fusion or similar double-sheave pulleys ($70-130)
• 150′ of 11mm (or 7/16″) static rope ($120)
• A used Petzl GriGri 1 (the original GriGri) ($50)
• A couple 5/8″ CM shackles, a couple steel carabiners ($50-80)
• A used Petzl ascender ($30)
• A prussik multiplier (20-24″ of 6mm or 7mm cord from climbing shop) and mini single climbing pulley ($20)
• Two shackle line locker setups (5/8″ shackles, webbing sleeves, 2″ rings, etc) ($60)
• Two 8′ spansets (~$60)
• Total: $460-540

The “graduate student who just got an extra grant check but also enjoys fine beer” longline setup:

• Rock Exotica or SMC double pulleys ($162-180)
• 150-200′ of 7/16 (aka 11mm) static rope ($120-180)
• Petzl GriGri 1 or Petzl RIG / I’D ($50-200)
• Small or large rigging plate (I’d say small for Rock Exotica, large for SMC) ($30-50)
• 2x AWL, Gibbon LineLock, Landcruising Lynx, etc ($240-300)
• Petzl Ascender (1 handled, 1 non-handled) (~$80)
• Some ball-bearing 2-3″ single pulley for multiplier (SMC, Bluewater, etc) ($30-70)
• 8′ spansets (~$60)
• Couple of 5/8″ shackles, couple of steel carabiners ($50-80)
• Total: $822 – 1200

The “my uncle just left me some serious money, I know some day I want to walk a 500′ line, and I hate upgrading” longline setup:

• Two SMC 3″ PMPs (maybe buy 2 more for later when you want to go 9:1) (~$180-360)
• 200′ of Sterling HTP, 600′ of sterling HTP (~$150-700)
• 2x: AWL or MonsterLock, or… 2x Zilla (~$250-500)
• 3″ SMC single pulley ($70)
• Double SMC large rigging plates (~$100)
• Petzl I’D or MPD (if you can afford it) ($250-650)
• 2x handled ascenders, plus a chest ascender (~$150-200)
• Several spansets of various lengths (~$100-200)
• Some 5/8″ shackles, some 1/2″ shackles, several steel carabiners 50kN or more rated (~$100)
• Maybe a dynamometer (Dillon ED JR 10,000LB — $1400)
• Total: $1300 – 4280 (depending on options)

So maybe the most important thing to note is that none of the above lists include any webbing.  You will need to buy this in addition to everything on the list above.  If you go for list number one, I’d buy a 200′(ish) piece of nylon tubular from your local climbing shop, or from BC if you’re ordering other stuff from them (so the shipping will be amortized).  If you go for list number two, I’d order either Type-18 webbing (200-300′), a medium length piece of Mantra/Flowline/Proline (I prefer the Proline) or something polyester from Europe (reviews coming soon for all of these), or just stick with a 200′(ish) piece of tubular nylon for now.  Maybe do the tubular nylon and a piece of mantra/proline and decide what characteristics you like best for future purchases.  If you’re on the last list, well, buy a 300′ piece of Type-18, a 300′ piece of something polyester (Mantra/Proline), and then something really long (500′+).  You won’t want to carry your 500′ webbing around with you all the time, so it actually makes sense to have duplicates of this (as well as a 200′ and a 600′ rope) of the stuff you really like.

I hope this helped clear some things up.  If there is anything I’m unclear on, just drop me an e-mail and I’ll try to amend this post/video — I know this will surely be a work in progress because there was just so much to cover (not to mention the rate at which the sport and rigging evolves!).

So what did we learn?  Well, it looks like a year worth of Seattle’s UV ain’t so bad for nylon webbing.  A 500lb drop in strength now makes this webbing equivalent to “normal” tubular nylon webbing, and in my opinion is a totally reasonable price to pay for this much UV exposure.  We should, of course, note that the webbing was brand new, so slightly worn webbing might be disproportionately degraded by UV; or some other variable might be at work.  Basically, don’t trust your life to this.  I would not leave a highline up for days or even weeks, and definitely not for months (partly because of the wind that many highlines experience, they are often torn to pieces after just a few days) — but I’d feel a lot better about the idea of throwing some big tricks on a friend’s backyard line that’s been up for 3 years straight.

*Incredibly similar to Balance Community’s SlackSpec; for all intents and purposes they are basically the same webbing, and I believe they are even made by the same mill. 

Each of these reviews will cover: MATERIAL (nylon, polyester, vectran, dyneema, etc), CONSTRUCTION (flat, tubular, threaded tubular, etc), DURABILITY, STRETCH [at typical longline tension], BREAK STRENGTH, WIDTH (usually 25mm), WEIGHT, and BOUNCE/REBOUND. In general, I’d really like to just speak generally about STRETCH and WEIGHT here.

STRETCH: this is an important one, for a couple of reasons. First because it tells you (more or less) the size of the gap you’re going to have to close to get your line to tension. For instance, if you have a 100M line, and it has 10% stretch at ideal tension, you will need to close a gap of about 10M (actually more like 9M, since your line will initially be 91M and your pulley system 9M, for a total of 100M, but for purposes of round numbers let’s just say 10M). So firstly that means you’ll need a certain amount of rope — if you’re using a 5:1 system, this means you’ll need 4x as much rope as the gap (4x at a minimum; 5x would be more comfortable so you could thread the brake straight off … this will make sense in the next segment). So right there we need 40M of rope. That’s not so bad. But what if your line had 15% stretch at tension? Now we need 60M (just shy of 200ft) of rope. So you can see why stretch is important. For any line with 15% or more stretch, you will need a pretty long rope to get it to tension if the line is more than 100M long. Mostly this series is geared toward lines up to 100M, so it’s not as much of a problem, and also 15% is about the maximum stretch you will encounter in any typical longline material; most of the newer lines that are popular nowadays are in the 5-10% range.

The other reason stretch is significant is that the line will relax everytime you pull some tension. It usually won’t relax back to where it was before the pull, but on average you won’t keep more than half of each pull’s worth of tension (in my experience). If your line is short, say 10 or 20M, it will be very easy to get it to a high tension, because the line only has to stretch a few meters. Even if it’s a “high stretch” line, 15% of 20M is only 3M. This means you will need to pull ~15M of rope through your main pulley system, and with a multiplier that will “feel like” you’re pulling 45M of rope. If you pull about a meter per tug, this is 45 tugs. You can probably do a tug per second, so the line can be tight in roughly a minute. No problem. But, let’s say this is a 100M line, which means everything above gets lengthened by 5. Now instead of feeling like you’re pulling 45M of rope, it will feel like 225M (700+ft!). And it’s really only the last 40% or 50% of tugging that is particularly tough. Well, on the 20M example, that’s only 20 or 30 seconds of difficult pulling. But on the 100M example it’s going to be a LOT more pulling. We can multiply the distance by five to get a rough idea of numbers, but your stamina when pulling hard for 30 seconds is probably not the same as minutes later, so the time it takes to get a longer line tight becomes exponentially more. Did that make sense? Think about it this way: can you do a chin-up? Can you do 2? Can you do 40? Doing 2, for most people, would take a few seconds. Doing 40 would take hours. Because they need rest breaks. Well, tensioning a longline is the same. I am pretty good at pulling nowadays, so I can get a 100M line tight in maybe 15 minutes. A friend and I just rigged a line just over 200M, and instead of 15 minutes it took us closer to three hours of pulling (with rest breaks).

WEIGHT: this is a big factor. Basically you are accustomed to moving the line underneath you when you walk, and on a short line this is no problem, since the weight is negligible. On a long line, with lots more weight and lots more tension, it becomes exponentially harder to move the line underneath you. The lighter your longline, the easier it will be to walk. For this reason, there is almost nothing that feels as good to me as plain old tubular nylon; it isn’t very strong, but it’s very light, and so it feels almost like I am walking on a cloud, compared to some of the heavier lines I normally fight with.

Ultimately, I think having some understanding of the dynamics of weight when walking and stretch when rigging, we can proceed to the next segment and then later talk about specific webbings and which ones might appeal to you based on easy of rigging, cost, durability, break strength, and so on.  See you in Part 4!  (And if you just absolutely can’t wait for the webbing reviews, I would recommend for most “broke” slackliners to start off with a 150-200ft piece of tubular nylon climbing webbing, assuming you’re in the US where it’s readily available, or maybe a piece of Type-18 up to 300ft in length.  If you have a larger budget, buy a 100M piece of both Type-18 and Mantra or ProLine and then decide which you like before moving on to longer and more expensive webbings.)

Cliff notes: if you don’t want to watch the video, the tension does indeed fall, from 1100lbs to 925lbs. This was a 56.5′ line with a standing (read: settled) tension of 1100lbs, and it experienced a drop of almost 20% of its tension. Line length, tension, the amount of water, the humidity, and probably some other factors will all affect how much tension falls, but I think this experiment strongly suggests tension will likely fall in most if not all cases.

You have to attach the line to the anchor sling (and your tightening system) somehow.  Since the beginning, slackliners were tying knots and using hitches to rig their lines. Sometime in the early-to-mid 2000s, the use of a chain-link line locker became popular. These reduce the ‘folds’ in the webbing, allowing it to retain more strength, and because they require no knots, everything disassembles very easily when finished.  Chain link usage reached its peak sometime around 2008, and then rappel ring line lockers began to replace chain links. Forged rappel rings were better than chain links because they offers more rigging space (sleeved and threaded webbing could be used), as well as the absence of a weld mark meant they were less likely to damage the line. At the time of this writing (May, 2012) forged rappel rings are still very popular for short lines.

Shackle + sleeve

For longer lines, people began to sleeve their webbing with 1.5 or 2″ tubular webbing and wrap that through doubled-up rappel rings, using 5/8″ shackles instead of carabiners. This is a bomber way to rig nylon long/highlines, but any small adjustment you want to make to the webbing length means you need to disassemble the whole apparatus. It also requires you to factor in the extra slack in the line because you are rigging on the ground (the line is not ‘pre-tensioned’) and this also requires more rope in the pulley system (rope is often at a premium when rigging longlines).  If you choose to use a shackle-based line locker, make sure you use brand name shackles — I would not trust anything made in China, it isn’t worth saving $5.  The benefit of a shackle is they are cheap ($18ish) and so, so strong (provided you buy a Crosby or other brand name shackle) — like 54,000lb strong (for a 5/8″ shackle).  Be aware, there is good preliminary data to support the idea that shackle-based line lockers are only safe (90%+ webbing strength retained) with nylon webbing; polyester webbing should be used with a specialized webbing anchor like an AWL, Zilla, Banana, or Kofi (see below).  My two “go to” setups for nylon shackle lockers both use a 5/8″ safety shackle — with this I will use either two 1.5″ inner diameter (‘ID’) forged steel rings, or two 2″ ID forged aluminum rings (purchase here, select ‘M ring’).  The smaller rings fit best on a 1.5″ or 1.25″ sleeve (I use the yellow 1.375″ sleeve webbing Balance Community sells), and the larger rings fit best on standard 2″ tubular webbing.  In my experience, 3′ of webbing is fine for a sleeve, and usually 2′ – 2.5′ is closer to perfect.  If you don’t want to mess with assembling all of this yourself, Jerry at BC sells it as a kit.

‘Banana’ style specialized anchors

Sometime in early 2009, custom-made webbing locking devices began to appear — first homemade ones, then artisan commercial versions. Several of us were dancing around this idea simultaneously — here is a post from me in March 2009 — and it’s interesting now to look back and see how it evolved.  The benefit of these modern webbing anchors is that webbing positioning within the anchor is adjustable on-the-fly. This allows one to setup a preliminary rigging of the line between the two anchors, and then pull all the slack out of the line (making it “hand tight”) by feeding the slack through the webbing anchors. I cannot overstate how useful this is.  It might seem like a silly little feature, but it saves to much time and helps so much in using just the right amount of rope in the pulleys (so they are closed or nearly closed when the line is at ideal tension).  Watch the video to get an idea what I mean (video segment 4 should have a lot of footage that shows how quickly this rigging method goes).

The first of these devices was actually designed many years ago by Scott Balcom, but it is just in the recent past that they have taken off (by making them way more beefy and combining with longline rigging techniques). Over the last two years, many different American and (especially) European versions of webbing anchors have sprung up. A short list includes the slackline banana, AWL, Zilla, Lynx, Monsterlock, lineLock, and probably several more I am forgetting.

Wrap-up

In conclusion: I think there are a lot of good options available for any potential longline.  Because the tendency is for newer webbings to be more static (making them potentially dangerous in a shackle-locker), and because adjustable anchors (aka “bananas”) are so incredibly useful, I think it’s clear this is the right decision for most new longliners.  The extra $50 between a shackle kit and a lower-cost adjustable anchor may sting a little upfront, but rest assured you will be using this anchor for years to come, and you will save incalculable amounts of time dialing-in your rigging thanks to the ease of adjustability.

Lastly, we want our gear to be strong (which webbing anchors and shackles both are), and we want either to eliminate multidirectional loads with smarter rigging (passing a spanset through a ring and clipping it to itself as I did in segment 1), or use rigging hardware rated for multidirectional forces (such as a 5/8″ shackle line locker, or the stainless shackle that comes integrated into the AWL).

This video segment teased my own banana-style web lock device a little bit. I call it the Kofi, and I’ve spent the last few months tinkering with various sized rollers and pins, different width webbings, different hole spacing and orientation, and so on. I will have a good amount of data to share publicly soon, but first we must finish our longlining guide; on to Part 3: Webbing!

As a general rule, I try to keep the gear that is further out on my rigging as strong as possible.  Another way to think about this is to say that the webbing I walk on is the weakest link, and as you head outward in either direction each piece of equipment should get stronger and stronger.  The idea is that if anything breaks it will be near the middle.  If something broke at the end, you’d have more metal gear flying, potentially causing more harm, than if something broke in the middle.  So the webbing might be rated for 4000lbs.  The pulleys for 6000.  The rope in the pulleys for 7500.  The rigging plate for 12,000.  The shackle on the rigging plate for 54,000.  The sling on which the shackle sits: 60,000.  I am skipping some equipment, but hopefully you see the general idea here.  Your slings should be STRONG.  If you use a homemade sling, use a couple wraps around the anchor (tree, etc) to accomplish this.  In general though, for longlining, just invest in some manufactured slings.

The main type of manufactured slings used by highliners and longliners is endless-loop polyester roundslings.  In slackline, they are often called “spansets”.  Within the rigging industry the color/strength is standardized.  I usually use green, although many other people use purple (a little less strong) and a rare few use yellow, blue, gray, tan, or some other color.  The length of the sling is the length of the loop, not the material used for the loop.  To restate this, a 6 foot spanset would use 12 feet of material.  I own several different sizes, but the size I use 90% of the time is the 8 foot spanset.  I would recommend buying two 8 foot spansets, and possibly a 4 foot, plus an extra 1/2″ or 3/8″ shackle (or steel carabiner).  The two 8 foot spansets will wrap almost any tree you’d encounter, and on the off chance you need to wrap a HUGE tree at one end, you can attach the 4 foot spanset to one of the 8 foot ones using the shackle, giving you a little over 12 feet of total wrap. In my longline bag I carry two 8-footers, a 4-footer, and a spare shackle — this has always been adequate.

Here is a quick chart of the tree width that a given spanset will safely wrap.  You can always use larger spansets on smaller trees (an 8′ spanset will obviously wrap a 1′ tree just fine), especially if you just wrap it twice around.  As you can see from the chart, most urban and suburban trees (those under 150-years-old) will be covered by an 8ft spanset.  With a 4ft extension you could wrap a very large tree, indeed.

There are just a couple rigging methods to cover.  If you buy a spanset, it should come with a stitched-on rubber tag that explicitly shows this.  There are basically three ways to use a loop to rig, and each affects the strength somehow.  The nice thing is that generally we will use the “basket” technique for wrapping a tree or metal pole, which doubles the rated strength of the loop.  Bonus!  Basically just avoid the “choker” method, and you’re good to go.

The last hazard to mention is that the more of a “tri-load” you place on the anchor sling, the greater the forces.  Although your line may have 2000lbs of tension, this tension translates into the sling at an angle, and the more oblique the angle, the greater the force multiplier.  The force on each side of the sling is a function of the slackline tension (“F”) divided by the-cosine of half of angle theta (theta being the angle between the two ends of the sling).  Confused?  See the chart at right.  Basically, as a general rule, try to keep to 60 degrees between the two ends of the sling (and avoid going over 90) and you should be plenty safe.  This is one reason we like to use spansets — they are so burly that you don’t have to worry much about doing any math while rigging; as long as you make reasonable choices the sling should be 10 or 20 times stronger than any loads you put on it.

Last but not least, please please please pad ANYTHING you attach your slings to. The only anchor I might not pad would be a thick metal pole with a very smooth surface and no corners what-so-ever (I once damaged a sling by wrapping an octagonal pole that had the most rounded corners you can imagine). If you are super broke, you can use thrift store bath towels cut into strips for padding (although if you are super broke, longlining might not be for you haha). If you are anything less than super broke, you might want to consider a Towel Tube (shameless plug for NWslackline’s $5 padding solution).