Setting up a zip line

Re: Let\'s have some fun!

I'd think if you were to put the disconnect at or above head level that the problems of getting whipped and of wanting ones torso upright would both be solved. There would, however, then be the potential for problem introduced by going for a swim with a couple feet of cordage, etc. strapped to your midsection...
 
Re: Let\'s have some fun!

Our zip crew has decided that we don't want the people going into the water with anything more than the harness, one carabiner, and the snap shackle. We'll leave the lanyard attached to the zip pulley, foam to protect from getting smacked.

It's looking good!

love
nick
 
Re: Let\'s have some fun!

I'm thinking that the snap back could (likely will) flip the pulley over and wrap the haul back around the zip line, maybe several times. Could that cause a big snafu that couldn't be pulled back uphill?
 
Re: Let\'s have some fun!

Sad, sad news. The owner of the "left" side has retracted their consent to let us use their property. They fear someone will get hurt. We'll be looking for a new location, but I'm gone on a whitewater rafting trip for the next 3 days, and zip day was scheduled for Aug 3, so I'm doubtful we'll find a new spot in time, considering none of us are from around here, we don't know the key spots.

I'm sad. It was sortof a buzz-kill.

love
nick
 
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Take a look at this Tyrolean traverse on the Lost Arrow Spire in Yosemite. You'll notice that the traverse is setup with two seperate ropes. I don't know what the upper, straight, line is for.

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Tom,

Looks to me like they used a single line anchored and tensioned from the same side and run through a pulley on the spire.
 
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how much of an angle should be created between the trees?

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Unless you know how to calculate the forces on a high-line, a good rule of thumb is to maintain a 1:10 sag ratio - a deflection from a straight line of 1/10 of the length between anchors with the expected load on the rope.

Another rule of thumb is to pre-tension a 1/2" highline with one person pulling on a 2:1 MA system. Once the system is loaded, it can be further tensioned with a 12:1 pulling ratio (6 people on a 2:1 MA or 3 people on a 4:1 MA, etc).

Always use tandem prusiks to tension a highline - don't put a knot in the rope - and use backed up high-strength (tensionless) tie-offs to the anchors.
 
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how much of an angle should be created between the trees?

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Unless you know how to calculate the forces on a high-line, a good rule of thumb is to maintain a 1:10 sag ratio - a deflection from a straight line of 1/10 of the length between anchors with the expected load on the rope.



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Even if you know how to calculate the forces on a highline, the only way to finish the calculations is to load it, in which case it is too late. I disagree with the rule of thumb too. You want 50 ft of sag on a 500 ft traverse? No way! I think the only way to get it is through experience. I suggest that the first person down wears heavy gloves and hangs in easy reach of the rope to slow themselves down. If possible, hang on the rope at the bottom end to see how high you are. (note, the rope will sag after a run or two and will need adjustment one time)

Dave

Nick, show the people backing out pictures of highlines from this thread and offer them a ride!
 
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show the people backing out pictures of highlines from this thread and offer them a ride!

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What does "people backing out pictures of highlines" mean? /forum/images/graemlins/confused.gif
 
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Even if you know how to calculate the forces on a highline, the only way to finish the calculations is to load it, in which case it is too late.

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I'm not talking about simple trig calculations for a deflected line, I'm talking about plugging the modulus of elasticity into the proper formulas so that you can calculate the sag for a given load BEFORE you load it. But this takes a skilled engineer.

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I disagree with the rule of thumb too. You want 50 ft of sag on a 500 ft traverse? No way! I think the only way to get it is through experience.

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Yes way, if you want to maintain a 10:1 safety factor. I double checked my references, though, and that ratio is for an 11mm (7/6") rope. With 1/2" rope, you can get away with a 6% sag (assuming a load of 200 lbs).

You can "get" a lot through experience, if you're willing to learn from your mistakes. But a highline, whether horizontal or inclined, has greater potential for catastrophic failure than any other life-support rigging.

Arnor Larsen, the inventor of the Kootenay Highline and considered the world's authority on them, suggests keeping them under 300' unless they're engineered.

- Robert
 
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show the people backing out pictures of highlines from this thread and offer them a ride!

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What does "people backing out pictures of highlines" mean? /forum/images/graemlins/confused.gif

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sorry it was not clear, "people backing out" were the people who changed their minds on allowing this to happen. I suggested showing them pictures to get them interested.

Dave
 
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sorry it was not clear, "people backing out" were the people who changed their minds on allowing this to happen. I suggested showing them pictures to get them interested.

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Got it now...thanks. Makes sense to me...show 'em a good one so they will see what they missed.
 
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Yes way, if you want to maintain a 10:1 safety factor. I double checked my references, though, and that ratio is for an 11mm (7/6") rope. With 1/2" rope, you can get away with a 6% sag (assuming a load of 200 lbs).

- Robert

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I met guys that did a one mile zipline from 1200 ft up the cn tower to ground level. No way did they have 500 ft of slack in the line, they would have dropped straight down for the first 100 ft or so if they did. They pulled the rope tight (tighter than I would have)

You seem to be forgetting that if you have 10 ft of slack in the zipline 100 ft long, that will drop another 15 ft down when a person is on it. this changes the angles and forces quite a bit. If you started with a 2% drop, a person would probably load it down into your limits.

Dave
 
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You seem to be forgetting that if you have 10 ft of slack in the zipline 100 ft long, that will drop another 15 ft down when a person is on it. this changes the angles and forces quite a bit.

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Not forgetting such an obvious thing, but perhaps I wasn't clear. The 10% or 6% sag is for a LOADED highline.

- Robert
 
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You seem to be forgetting that if you have 10 ft of slack in the zipline 100 ft long, that will drop another 15 ft down when a person is on it. this changes the angles and forces quite a bit.

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Not forgetting such an obvious thing, but perhaps I wasn't clear. The 10% or 6% sag is for a LOADED highline.

- Robert

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I think maybe we are on the same page now. Sorry for the misunderstanding.

Dave
 
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