It's ok to go both ways, just be safe about it.
The Bolting Bible
Bolting For Highlining
Welcome to our free course as our way of contributing to the bolting community. It's nice to understand what you are clipping and trusting with your life, even if you never plan on installing or removing bolts. We believe that if someone is going to spend their time and money to bolt something, they probably want to do it as good as possible. Hopefully, the Bolting Bible gives you the tools you need to do a great job. Get it?
This book is in a blog format. The main blog points to all 17 chapters, and at the end of each chapter, it points you to the next. A downloadable pdf is available HERE.
Going All Natural
Like any good hippie, going all natural is more fun. In highlining, if we can string up our massive bag of 1" wide plastic across the sky WITHOUT using bolts, we call it "all-natural" rigging. It's held as a higher form of rigging but it isn't rocket science how we do it. Wrap a tree or rock like you would to slackline in the park or place a whole bunch of climbing trad gear and get good at equalization.
Highliners often times play on top of the cliffs and if we place 3 or 4 bolts on the top where a lot of people can see them, it can negatively affect access. Especially if there are multiple lines in one area. The Fruit Bowl in Moab is now a highline destination but notice it has hundreds of bolts littering the tops of the cliffs. You can't do that just anywhere today.
It is a higher form of rigging to take with everything you came with. Aim to rig highlines all natural and really consider if that spot needs bolts before installing them. Also, know your area first to see if you can legally install the bolts!
You can see many examples of different ways to rig in our HIGHLINE RIGGING PLAYLIST.
Sharing and Caring
It's less of an issue today, but climbers can get upset about highliners using their bolts. Oftentimes, climbing anchors are in the perfect spot to rig a highline and therefore it is tempting to use them. An issue in the past, and a big motivator to test bolt strength, was our "high forces" were compromising the bolts. That is not true and we are not damaging the bolts.
The next issue is sharing the bolts themselves. If you have a clustered anchor and someone wants to rig a top rope or climb through using that anchor, it can cause issues but sharing is an art and communication goes a long ways, and if there is a possibility someone might need that anchor, rig a separate bfk for them to clip to. Consider not highlining in a spot during a busy time if it is preventing climbers from enjoying that space as well.
What You Do Is Tight!
Highliners play with more force than any other sport. Climbing gear may see 8kn sometimes in gnarly factor two falls but it's short and rare. Highlines, especially freestyle or > 1 KM long highlines are constantly playing at 8kn. High tricklines can be even 12kN!
Most highlines are 2-3kN when they are tensioned and 3-4kN when are walking on it and 4-6kN when you whip. If you have a 3 point anchor AND it's equalized perfectly, then it's rare for any bolt to see more than 2kN.
So how much can a bolt hold? Minimum 20kN. In the Book of Numbers, you can see most of them are in the 30kn-40kn range, and some we can't even break because the hanger breaks first at 50+ kN. Now, you can't put short 3/8" (10mm) in sandstone and cyclically load it to 8kn without it failing so it's important to follow good bolting principles taught in the Bolting Bible but if you do a half-decent job it is super good enough!
Think Long Term
There are a couple of deserts on earth where a zinc-plated bolt will last about 50 years, but aim to install hardware that will last longer than you and put in stainless. No one wants to highline on rusty bolts. The bolts we replaced in Yosemite were barely 20 years old and they were very rusty and even the bolts replaced in Moab's desert were rusty. Also consider that if they are installed on top of a cliff, the hole will hold water even if it doesn't rain that often. And of course, use Titanium if rigging near the ocean.
Bolt Placements
Things to consider before deciding where the holes will go
Where do you want your master point to be? It will be the center of your bolting pattern so choose carefully. And remember you don’t want more than a 45 degree angle on your anchor legs so it shares the load evenly.
Is the anchor going to serve more than 1 highline? What pattern can the bolts be placed to best be pulled in multiple angles?
Can you prevent friction? Will there be a weird hump between the bolts and the master point? Is there a way to install it so the individual legs don't need padding, but only the master point?
How far back from the edge will the bolts be?
A. In hard rock it can be a foot or two away from edge but if it is too close then it can put the master point too far beyond the edge making rigging difficult.
B. In soft rock it is important to stay away from the edge even 6 to 10 feet back in some cases but then the master point will need extending possibly requiring a stabilizer bolt, one near the edge that doesn’t hold much force other than to keep things from moving around causing abrasion.
What Pattern will you use?
A. Straight line - Careful, this is how they harvest quarry stone. This can score rock and make it susceptible to fracturing. Know your rock. STRAIGHT LINE PATTERNS DON’T EQUALIZE if on top of cliffs. They can be the best option if pulling straight out of a cliff wall.
B. Equilateral Triangles equalize best if on top of a cliff. The bolt most direct in line (the center bolt) and the closest bolt sees the most force. Those two principles cancel each other out for the most part if you do an equilateral triangle, with the center bolt being furthest back. Learn more about directional relativity here.
How many bolts will you use? In highlining, we made a sport taking factor 2 falls on death triangles with ropes that don’t have sheaths, so it was common for people to put in 4 or 5 bolts on either side. After BoltBuster research, we found out that bolts are pretty awesome if your rock is awesome. Therefore, 2 bolts are redundant, 3 is now common for highline anchors, and 4 bolts are just overkill as it is difficult to equalize them. Only 2 or three bolts ever see the force anyways. Just make sure you have quality bolts in quality rock. If you can equalize 3 points well, then no bolt is ever going to see more than 3kn giving you a 10:1 safety ratio for each anchor point.
Old School Bolts
Back in the day when the forces were more of a mystery, many highliners put in BIG bolts and lots of them. Some old school bolts were big 5/8" (16mm) wedge bolts with 2-3 chain links sitting on a stack of washers as the hanger. Terry Acomb established the Fruitbowl area and these were bomber and affordable. Many of them have been replaced with the new stainless glue in standards for that area by Balance Community for GGBY. Many bolts in Yosemite were also much bigger wedge bolts than climbers would ever need but it was a mixed bag of what was put in. They are all now Fixe 1/2" glue ins so the rope can be directly threaded into them since lightweight is key in Yosemite.
Today's Bolts
Even though a 3/8" (10mm) mechanical bolt is super safe enough, it's standard to use 1/2" (12mm) bolts. 5/8" (16mm) is rare and only for shit rock or if you really want the bend radius a monster crux bolt has to offer. Mechanical or Glue-Ins are all super good enough for highline safety but of course depends on the quality of the rock.
It's ideal to be able to thread a rope directly into the anchor since many anchors are built with rope bfks. Any solution for this is backwards compatible with traditional delta quick links + spansets, which is another way of rigging. Glue in bolts are all made of some sort of round stock metal so these solve that problem and are bomber in any rock and don't have hangers for people to steal. There are a handful of hangers out there that can have a rope directly threaded through them if you want to use a mechanical bolt, see our Hanger's chapter.
It's not only about ultimate failure but when a bolt starts to bend. A wave bolt glue in is strong and is in a 1/2" hole, but the 6mm metal bends at forces you can get in a highline like in this EPISODE. If you are going to use a 1/2" glue in, use a welded type so the rod is truly 1/2" and not 6mm bent into a P shape.
A rare but clever solution to keep bolts hidden was to drill a big hole in a small rock and carefully glue a nut to the inside of the hole, keeping the threads clean, so you could screw on the rock to the all thread or wedge bolt. Just remove some rocks and install a hanger when you want to use it! V threading rock can work but it risks getting debris in the holes and we haven't tested ropes in v threaded rocks yet for high force application.
Get Started In Highlining
We have Highlining 101, a free course on our website to help anyone learn everything they need to know how to use a highline that is already rigged. Go to our COMMUNITY page to find people and places to slackline. It was a massive effort by ISA and HowNOT2 to create that database and get it on a map but it's to help anyone new get plugged into our community. It also has a calendar of festivals, comps, and education events.
What's Next?
You can always go back to the main part of the BOLTING BIBLE HERE
Feedback, typos or more information is always appreciated. HMU at ryan@slackline.com
This course is free but not free to make. If it really helped you, please consider SUPPORTING US.