Length vs. height of a cable

nea_nemesis

Hi, everybody, I really hope you can help me out with this one.

I work for an outdoor facility, and we were just replacing our zip cable. Due to major safty issues, we need to get it at the exact height it used to be at, and that's kind of tough.

After a few trial-error sessions, we managed to get it within inches, but now it's down to details. I know that pulling about a foot (~30cm) on the end of the cable changes the height of it for about 2,5 feet (70-80cm). Since we're talking galvanized aircraft cable here, you understand why I want a formula before we fit it for two more inches in height...

The cable is about 200 yards (~200m) long I'd say. I can get exact (or close to exact) measurements, probably the weight of the cable, tension and such things, but I don't have them now.

berkeman

Why don't you just use a turnbuckle?

nea_nemesis

What's a turnbuckle? (non-native English speaker over here...)

berkeman

It's an in-line device commonly used to adjust the length and/or the tension in a cable:

http://en.wikipedia.org/wiki/Turnbuckle

The two screws on the ends of the turnbuckle have opposite threads, so that turning the center portion pulls them in or pushes them out.

nea_nemesis

Because the anchoring system is different (looped cable with a thimble locked in place with serving sleeves, clipped into a rapid link that's attached to an eye-bolt).
So the adjustable part is the piece of cable that goes through the thimble and back in to a serving sleeve, and that's a hassle to loosen and tighten.