Zip lines... Any advice on gear for a steel line?

I've been doing some research on putting up a 300' line, and it looks like the force involved are quite high. Like 40kn or 9000lb for a 5x safety factor on 180lb person. That's for a smallish 5% droop, or 15' in the middle.

Has anyone built a line this long before and have any recommendations for a good steel trolley? For the line I'm imagining 3 bolts to 5/16" amsteel soft shackles to 3/8" steel 7x19 cable and beefy steel u bolts and thimbles. Maybe a cable puller and a 9-1 pulley to tension?

Any input is appreciated, don't wanna die!

Looks like your post got submitted before you finished your thought. 

Edited to finish, thanks Bobby.

The market is fairly saturated with zip line trolleys. I've used one by CMI quite a bit. Petzl also makes one that I have used. Beyond the trolley itself you will need a zip line specific lanyard. I've used lanyards by several different companies including Misty Mountain. A 300' line is fairly significant. Do you have a plan for stretching the cable? You will also need to calculate how much tension you have in the line, the drop from start to end, etc. Without a braking device (which is likely out of consideration for a home-made line) you will need enough "sag" so as to arrive at the other end without too much speed. Hitting the other end of the line too quickly breaks bones in a hurry. I'd recommend a fail-safe device before the end of the line, as the impact of hitting this, while perhaps significant, is obviously more desirable than colliding with a pole or tree at a high rate of speed.

It may be obvious, but with a zip line everything should be steel. Steel biners, steel trolley, etc. Perhaps less obvious is that the cable will stretch with use. As such you want a way to tension the line as needed.

Below is the CMI trolley I have used the most and am happy with. The line on which I have used it is a bit longer than 300'.

Hey Mitch,
I always get nervous when I hear people talking about building ziplines but it sounds like you are doing your research.
1. Do some more research on U bolts. I believe they have fallen out of favor. If you are set up to install glue ins I would go with the 8mm Twist bolts from Team Tough. You should be able to connect your soft shackles directly to the bolts. We are seeing 8mm soft shackles break at 40+ kn on these bolts.
2. Lots of good trolleys out there. I have used trolleys from Robertson, Petzl, Headrush and Camp. Just make sure the trolley you are buying is rated for steel and not rope.
3. To tension I think you could get away with a 3 to 1 with progress capture to get most of the slack out of the line and then a chain puller for the final adjustment. Use a prussik or a Klimheist to pull the line and then use fist grips and a thimble to finish the line where you need it to end. This allows you some adjustability. 

Thanks ClimbingOn! Yeah that all sounds reasonable to do. Here's the plan:
-10 foot drop, I'm going to use gravity and droop, should end up near the middle which is what I want. 8kn tension in the line for 180lb person, yeah that's up there!
-dynamic lanyard clipped to the trolley. Why zip line specific?
-dynamic backup line with a lanyard to that line. Maybe feasible to trax out? People don't use a backup line?
- 2 ton cable winches are cheap. Tension and then secure with more steel line along side.
- Steel trolley, steel sheaves like from CMI
This will work right?

Oh yeah Bobby, referencing the U bolts I was talking about securing a steel line around a thimble with U bolts, not anchor to ground. You think fist grips instead of U bolts here?

I like your suggestion though, those Twist bolts look legit and securing a soft shackle to them is great. I wish I had the know-how to do glue-ins, but in desert rock I'm planning on 1/2" powers 5 piece, 4 7/8" long.

Mitch Stubbs wrote: Thanks ClimbingOn! Yeah that all sounds reasonable to do. Here's the plan:
-10 foot drop, I'm going to use gravity and droop, should end up near the middle which is what I want. 8kn tension in the line for 180lb person, yeah that's up there!
-dynamic lanyard clipped to the trolley. Why zip line specific?
-dynamic backup line with a lanyard to that line. Maybe feasible to trax out? People don't use a backup line?
- 2 ton cable winches are cheap. Tension and then secure with more steel line along side.
- Steel trolley, steel sheaves like from CMI
This will work right?

I wouldn't worry to much about a zipline specific lanyard. Many Zipline guides use a Petzl Rig with a 11 mm Static rope to allow them to adjust and ride close to the line in case they need to do a rescue or pull themselves in. The connector between the trolley and the rider sees very little force.

Re: back up lines: Many ziplines have back up anchors such as a cable around a tree. For a 300' line with 3/8th aircraft cable I do not think you will be anywhere near the breaking strain unless you severly kink the line making your end loops. I think you will find it easier to just ride close to the line and wear gloves and just pull yourself in, maybe use a Prusik to capture progress. 

Mitch Stubbs wrote: Thanks ClimbingOn! Yeah that all sounds reasonable to do. Here's the plan:
-10 foot drop, I'm going to use gravity and droop, should end up near the middle which is what I want. 8kn tension in the line for 180lb person, yeah that's up there!
-dynamic lanyard clipped to the trolley. Why zip line specific?
-dynamic backup line with a lanyard to that line. Maybe feasible to trax out? People don't use a backup line?
- 2 ton cable winches are cheap. Tension and then secure with more steel line along side.
- Steel trolley, steel sheaves like from CMI
This will work right?

Backup lines are not regularly used for zip lining as the steel cable is so significant. Also, with a dynamic line and a trolley on that as well, the dynamic line will whip around and likely get caught on the cable/trolley. I'd recommend skipping the backup and just using the cable. I think this is the only time when discussing climbing type things that I've ever said to skip the backup.

I say a zip line specific lanyard because trolleys have the primary attachment point and then a backup attachment point. The lanyard ends must be different lengths as the one side will be used to support the full weight of the zip lining individual. The backup attachment point must not be weighted. Zip line lanyards are cheap and the right tool for the job. The lanyard clipped to the trolley does not need to be dynamic.

I can't confirm or deny whether your setup will work without seeing it or a sketch of it. Are you anchoring to trees or poles? How high above the ground? A 10 foot drop, just off the top of my head, seems very little over the span of 300 feet.

Mitch Stubbs wrote: Oh yeah Bobby, referencing the U bolts I was talking about securing a steel line around a thimble with U bolts, not anchor to ground. You think fist grips instead of U bolts here?

I like your suggestion though, those Twist bolts look legit and securing a soft shackle to them is great. I wish I had the know-how to do glue-ins, but in desert rock I'm planning on 1/2" powers 5 piece, 4 7/8" long.

Ahh ok. Fist grips tend to spread out the force instead of concentrating it in the bend of the U. How much that matters on a 300 foot line I do not know. 

1/2" Powers 5 piece are plenty strong. Team Tough also stocks the rod hangers which are 8 mm and you should be able to attach soft goods to directly.   How many bolts are you planning on for each anchor? 

CMI trolleys work great with 3/16 inch cables (do not get coated cables and make sure you don't get any cable made in china- it's all poorly made), make sure you get forged steel U bolts or fist grips and when you tighten them down get a torque wrench and measure how tight you are making them.  There are recommended numbers depending on the cable you use.  

You want at least one lobster claw type apparatus for your backup, the shorter the better so that less force will be generated should your trolley or main support fail.  When you order trolleys make sure there is a loop on one side that you can put your backup carabiner through so that you can reduce wear on your lines.  You don't need a cable winch to tighten the cable, get a cable tensioning clamp and a ratchet strap and you'll save some money.  You'll also want to make sure that you have sleeves on the tails of your cables so they don't fray.  

Good luck, let me know if you have more questions.

Thank you guys for all your awesome advice!

I'll abandon the backup line, as I can image how that would be a liability. Instead my instinct says 6 bolts per side, 3 bolt anchors with a redundant one. That's a lot of wiggle room when equalized.

Then the line can be pulled with a cable clamp and a 2 ton ratchet that I've got and secured with forged thimbles and fist grips, all torqued. (I was a mechanic, I love torquing). Then a trolley that'll allow me to clip the backup to it and not the cable, sounds smooth. The basic CMI Comtrolley below looks legit. Finish the ends of the cable for longevity, too.

Bobby, you think the 1/2" rods won't become spinners under 5 piece bolts? This is sandstone but I can re-torque after the line is set.

Mitch Stubbs wrote:
Bobby, you think the 1/2" rods won't become spinners under 5 piece bolts? This is sandstone but I can re-torque after the line is set.

No. I don't think this will be an issue. I would check after the first zip. 

Hey Mitch,

I'm not a zip line expert, but I've been rigging in the music, convention, and install industry for 34 years. I own a rigging company now. I believe most commercial steel zip lines are made from 1/2" wire rope, not 3/8". Also, what you are calling u-bolts, are called Crosby's, and are not intended for overhead rigging, or life support. It says it right on the packaging. You need to have the ends professionally done with thimbles, and machine swaged. Now if the location is not life threatening if it fails, say close the ground, then I guess you could take your chances.   

Mitch Stubbs wrote: 

I'd say probably spend the bit extra and buy a nicer trolley. You're a climber and not an average zip liner, so I can imagine that you'll do things to make it a bit more fun such as running start and whatever else you can think of. With the Comtrolley the attachment is in the middle of the wheels. With the nicer trolleys the main attachment point is below the wheels, meaning that the load will stay better distributed even under weird loadings. The trolley itself will be a fairly inexpensive part of your setup so you may as well drop the little bit of extra cash.

I'd also recommend a second trolley or at least something like the below in case you have to send someone out on the line for a "rescue." I have had one trolley seize once and had to do this. This was after very extensive use.

NOFF wrote: Hey Mitch,

I'm not a zip line expert, but I've been rigging in the music, convention, and install industry for 34 years. I own a rigging company now. I believe most commercial steel zip lines are made from 1/2" wire rope, not 3/8". Also, what you are calling u-bolts, are called Crosby's, and are not intended for overhead rigging, or life support. It says it right on the packaging. You need to have the ends professionally done with thimbles, and machine swaged. Now if the location is not life threatening if it fails, say close the ground, then I guess you could take your chances.   

WHoops in my post I said 3/16s- I've been talking maple syrup making all day hence the screw up.  COmmercial ziplines are made of 3/8 inch cable, for the most part.  It depends on the length and at 300ft, 3/8inch is more than strong enough.  

Hey thanks again guys for all the helpful input. I'll be sure to post a pic of how this all goes down, and if you're in the Moab area and want a turn, I can send the location for the Thanksgiving party!

Have you loo at this trolley from Kong
https://www.kong.it/en/2-products/items/f21-pulleys/p296-zip-evo
It makes attaching to the zip line much more easy and minimizing the risk of dropping it. 

That's an ingenious system, and you can use it to build 3 to 1's. Great find!