Monday, March 21, 2011

Slackline Project - Ground Anchors

This post is a follow up on my earlier posts Slackline Project - Requirements & Feasibility and Building A-Frames . You might have a look there to get the context.

Disclaimer: This goes on top of the standard disclaimer. I'm neither a experienced slackliner nor some sort of construction engineer. So if you want to utilize some information from below: Just do it but your should crosscheck the information with some experts before you apply it! No guarantees from my side.

The A-Frames are providing the height of the slackline, but still we need some fixpoint to attach the line to.  Slackline set desigend for A-Frame using ground anchors like Slackline-Tools Groundanchor or Gibbon Slackline - Ground Anchor which create a fixpoint by screwing the anchor into the ground. That is pretty neat as it is easy to be done and you can easily remove the anchor afterwards. At the same time it is pretty expensive.

During the search for alternatives, I found that e.g. kids swings are commonly attached to the ground with the same kind of anchors (e.g. Those are way cheaper but differ at least in three points from the slackline- anchors:
  • The length of the anchor is shorter. Therefore the anchor would go less deep into the ground and hence hold less. I found statements like if you dig the anchor 20cm below the ground level, you could double the strength of the anchor. Not sure if this is correct, but it makes sense that the length is important.
  • The screw diameter is lower.
  • The eye is not closed and might therefore hold less.
For sure there are also more differences in material and such, but finally I decided to go with[0]=anker. They offer anchors with 80 cm length and screw diameter of 12 cm. I'm using two of them for each end to get some extra security. That is not much of a problem as I don't intend to remove the anchors frequently. All together way cheaper than buying a pair of slackline anchors.

Some first tests show that this seams to work. I could build up the line and use it a couple of times already without indicating any issues. It is quite important that you have some massive bar at hand to be able to screw the anchors into the ground. Without it is a hard to get them in to the ground. Out of curiosity I removed on of the anchors from the ground. It wasn't really easy to just screw it out, but I needed to dig it out partly. Leaves pain in the back and a more secure feeling ...

Note that not each kind of ground is equally good to places such anchors.
Finally we need to select a line and some more connection parts to get everything together - that is going to happen in the next post.