What tool to tension 1000 ft. of steel cable between 2 trees? Comealong didn't work -OR- full size john deere

Question

Hi Everyone!

Here’s my dilemma:

I am making a ZipLine at my property in the country (if you don't know what a ZipLine is - search it, they're REALLY fun!).

Basically it's a cable suspended between two anchors (in this case - massive trees) with an elevation change. Then, a rider zips down the line using a pulley and a climbing harness. If you get the right height and speed, it's a real blast.

Ok, so back to my dilemma. I need something that will tension 1000' of 3/8" galvanized steel cable. A come along won't work. I have a full-size John Deere tractor as well that wouldn't pull it tight enough. I know I need some kind of winch, but I don’t know the name of the tool.

Maybe a bulldozer? I need something rather economical if you know what I mean so any suggestions would be much appreciated.

Thank you in advance!

Answer 1

A 1000' span is really long. I think you have unrealistic expectations of how tight you can get the cable. The tension of the cable is going to be massive if you don't have enough sag. (can you say "banjo")

What are you using to anchor the two ends?

3/8" galvanized steel cable has a breaking strength of around 14850 lbs and a safe working load of 2970 lbs.

An extra 200 lb person in the middle of the span is going to generate huge tension forces on the cable and points of attachment.

The fact that the come-along and tractor were not sufficient should be telling you something. The typical come-along is rated at tensions near the safe working load of the cable.

I'm a bit concerned that you might be a future Darwin Award runner-up.

Answer 2

Steel Cable Tensioner

Answer 3

Pick up an off-road winch used to pull one's vehicle out of trouble when four-wheeling ( http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91781 ). Mount this to one tree and fix the free end of the cable to the other. The winch referenced will be able to apply up to 3000 lbs of tension on the line.

The next question is, how far will the line sag at the center if suspended horizontally. The vertical displacement of the cable measured from its lowest point (at the middle) is given by the catenary equation

y=T/u*(cosh((u/T)*x)-1)

where u is the weight of the cable per unit length, T is the tension in the cable, and x is the distance from the center of the cable span. 3/8" steel cable has a linear weight of about 0.28 lbs per foot, the winch specified above can supply a maximum tension of 3000 lbs, and the maximum distance from the center point is 500 feet. So, the sag is given by

sag = 3000/0.28*(cosh((0.28/3000)*500)-1)
sag = 10714.3*(cosh(0.04667)-1)
sag = 11.7 feet

Therefore, you'll need to fix the winch and the end of the cable at least 12 feet off the ground to keep the sag from touching the ground. If you are 6 feet tall, then you'll need to fix these at 18 feet above the ground.

Have fun.

Answer 4

Zip Line Cable Size

Answer 5

You might try some good old fashioned block and tackle. Basically a series of pulleys that increase pulling strength.

You also might want a tensioning device in line so you can keep your tension consistent as temperature changes or as the line cuts into the trees.