cable rigging for safety

tkeaton

tkeaton

Master Velocipede Alchemist
Joined
Mar 20, 2005
Location
Chattanooga
I have a bit of a ditch that is crossed by a fallen log. The ditch aint real small. There are unquestionably solid trees on either side of the span. The width of the span is 100-120 feet.

I am wanting to run a cable between the two trees on opposite sides of the span. The idea is to harness in and attach a tether to the cable spanning the gap.

What is the minimum diameter/construction type of cable that I should use? How taut should I attempt to get the cable? What is the best method for securing the cable to either side of the span?

Only one person at a time will be tethered to the cable. Maximum weight of 200lbs. Cable will not be under external load, unless person crossing the span falls off of the log.
 
I mean I'm not trying to be an idiot here I promise. Is this supposed to support the person if they fell or is it more of a "hold" for the walkway? How deep is this ditch? Only reason I ask is you are looking at 100+ for a harness/lanyard +prob 100 for the cable to cross 100'. Are these trees big enough to hold a person? You considered just doing like a burma bridge?
 
If you are trying to construct a bridge Google is a powerful tool. But if you are trying to create a zipline, thats no problem and you can buy all the rigging online. do some searching and see what you come up with. give us more details!! pics too i want to see this span!
 
this is what i *think* weight of cable per foot X length (+ ([cable hight under no load - cable droop under weight in the middle] + harness rope length) X weight X accl.) = the shock load that it needs to sastain.
remember that is what i think... no eng. degree
 
The issue here really is boththe cable AND the supports at the ends. If the line is relatively taught (meaning very little appreciable droop from the load) then the cable tension will be surprising high. That 200 lb person (static load) becomes thousands of pounds of cable tension, and any bouncing will spike that higher. Is the cable level or is it sloped from one side to the other?
 
I mean I'm not trying to be an idiot here I promise. Is this supposed to support the person if they fell or is it more of a "hold" for the walkway? How deep is this ditch? Only reason I ask is you are looking at 100+ for a harness/lanyard +prob 100 for the cable to cross 100'. Are these trees big enough to hold a person? You considered just doing like a burma bridge?
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No worries, the purpose is to support someone should they take a dive off the log.

The log itself is about 35-50' above the ground. The cable would likely be 50-70' above the ground. Yes, the trees that I have picked on either side of the ravine are definitely large enough to support any kind of cable system that I would construct.

Also, the cable will be about 20' (horizontally) to the side of the log. So...20' away, 20' above....more or less

The issue here really is both the cable AND the supports at the ends. If the line is relatively taught (meaning very little appreciable droop from the load) then the cable tension will be surprising high. That 200 lb person (static load) becomes thousands of pounds of cable tension, and any bouncing will spike that higher. Is the cable level or is it sloped from one side to the other?
Click to expand...

I had taken into consideration the weight of the cable. I was not planning on trying to put any type of tension on the cable other than what would be required to keep it above the level of the log.

Also, the cable will likely slope from one side to the other, both because of the layout of the terrain and to make it a bit easier to get my ass down, should I need to use the cable.

hmm...Ill add more as I think of it. Oh, I stopped by the rigging supply company and they said that "standard" for a single person is 3/8" cable. Any confirmation?
 
what im talking about cable is when you pull the cable tight with no weight in the middle then pull down in the middle... that little big of space may seam insagnificant but it could ezly snap if you dont take that into conderation
 
Futbalfantic said:
what im talking about cable is when you pull the cable tight with no weight in the middle then pull down in the middle... that little big of space may seam insagnificant but it could ezly snap if you dont take that into conderation
Click to expand...


:wtf: did you just say?
 
Futbalfantic Punctuation, spelling, and proper use of a word in a sentance are all COMPLETELY lacking in that post.
 
He's saying that when this dude slips off his log and free falls 8 feet before the ~26' tether snaps taught, it's going to put tons of force on the cable anchors, and if they don't snap right then and drop him another 30 feet to the ground, then he's gonna bounce for a few minutes, and then he's gonna dangle 20' out in midair, probably bleeding internally, while his friends try to figure out how to get him down.

Traversing this span on a zip line is about 1000 time safer than the fall arrest cable system / hangman's gallows described here. If that's too expensive, string some rope handrails along the log and put something in your will about contacting the Darwin Awards should your best-laid plans go awry. Good luck.
 
bahaha... opps, oh well. Atleast someone got what I was saying. And for the spelling part... I can't spell worth a damn
 
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