We want to install a slack line at our ski site. Installation will not involve the use of trees since we really don’t have any we can use. I plan to set pressure treated 4x4s in the ground set in concrete. It looks like a typical line is 45 feet long so I guess the posts should be about 40 feet apart. For safety, I’d like the line about 24-30 inches off the ground. So here are my questions:
1. Is two feet in the ground for every foot above the ground enough for the posts? Or is that ratio overkill?
2. If I have say 30 inches of post showing above ground with the slack line attached at the top, will a 4x4 be sturdy enough the resist the tension of the line, or is 6x6 the better way to go.
3. Any suggestions on the best slack line product? This will not need to be portable but should be UV resistant.
4. How much sag should I expect over a 40 foot span? Am I starting too low with a 30 inch post?
5. What am I overlooking?
Not sure how to deal with a long link?