you could use a 6 x 6 but it should be tied into another structure for stability, where is the zip line being connected to? any saftey concerns that high up from people falling?

 

Why not use a utility pole then? Are you doing this for private endeavors or for commercial? are you going 12' or 16' something at 12 feet high could be way smaller than one at 16'. what kind of wind and seismic loads do you have. what area are you in?

 

It's just for our own use. We are in a very open area (rural). It's pretty windy. I'd automatically go with a utility pole if they were easier to find. I can certainly build something with more posts as I imagine quite a bit of movement for a 6x6,but liked the idea of not having multiple structures in our backyard for aesthetics. In terms of height, we are very flat so I needed something higher to make the zipline worth it. I think most recommend a 6-8' drop over 100 ft. I figure at 12-16' I could make the ride a bit more enjoyable. This will be used primarily for our kids, not necessarily adults.

 

usually zip lines are attached to trees for anchor points, cant you build a platform on the side of the tree that the cable is connected to?

 

We can, and that's probably what I need to do. We are actually building a treehouse so I can always make the launch point off the deck of the treehouse. I think I was letting my creativity get the best of me. Trying to think of a way I could create a bridge to a zipline platform and have a gate that I could lock so it could only be used when an adult could supervise.

 

just padlock the zipline spool, so its not usable..