Commercial style trellis question

[nagmay]

We're setting up a trellis for a 60' row of hops to do some trials. This will be the style that you see in commercial yards:

• About 16' tall
• 6" posts on the ends, 4" posts between
• 1/4" aircraft cable
• Ground anchors and turnbuckles

So, my question is about running/tightening the cable. Would it be better to:

a) Run a continuous cable from the anchor, through an eye-bolt on the end post and across to the other end. Left image. Seems really simple. One turnbuckle could be used to tension the entire structure.

b) Run one cable from end post to end post. Then another from each end post to the anchors with a turnbuckle. Right image. This seems common, but won't it need to bend the end posts to tighten the main cable?

I would appreciate any advice from people who have experience with these systems.

 

[PapaBearJay]

The later in my experience works easiest because then you can have the two different strengths necessary for proper tensioning.


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[nagmay]

"two different strengths necessary for proper tensioning."
Do you mean 2 different types of cable, or 2 opposing forces?

I know that with b) the pole is often angled at 60deg. This transfers the opposing force directly down the pole. However, I have also seen several yards with vertical poles as shown.

In a) the pole is not directly attached to the cable. Not quite sure what this means for the forces involved.

 

[PapaBearJay]

"two different strengths necessary for proper tensioning."
Do you mean 2 different types of cable, or 2 opposing forces?

I know that with b) the pole is often angled at 60deg. This transfers the opposing force directly down the pole. However, I have also seen several yards with vertical poles as shown.

In a) the pole is not directly attached to the cable. Not quite sure what this means for the forces involved.

In a) all the forces are placed on the cable and anchors. In b) all the forces are spread on the poles, which is then reinforced by the guy wires and anchors.

With only 60' of trellis, this may not be such a huge issue, but still one that needs to be considered.

Also, you would generally use two different gauges for the guy wires and support cables.

 

[day_trippr]

I would go with "b". With even modest pre-loading tension applied by the two turnbuckles while the suspension line is unloaded to get most of the stretch out, the only thing you'll have to counter over time is additional accumulated stretch in the suspension line.

Assuming the suspension line is of something fairly substantial I don't think the stretch would reach the point that the two supports will be deflected outwards much - maybe a few inches tops.

A ~60' suspension line loaded up with mature bines the week before harvest could easily have a few hundred pounds of foliage hanging from it (especially when wet from rain or morning dew). Add in some unfavorable wind, and with "a" I'd be concerned that the amount of force applied to the suspension line could cause either or both supports to snap inwards, as there wouldn't be anything keeping the tops from skidding along the line...

Cheers!

 

[nagmay]

Thank you both. This is the kind of information I was looking for. B) is marginally more complicated, but transfers force to the poles.

Now, I am a questioning if a single anchor at each end is enough support perpendicular to the row. Normally, I see multiple hop rows connected together.

I have a bunch of extra anchors and could place 2 at each end. Thoughts?

 

[day_trippr]

Two stays at each end is always the safer option, especially when a late summer t-storm rolls through and a 60 foot curtain of hop bines wants to become a sail...

Cheers!

 

[GVH_Dan]

Go with 1/2" wire from the anchor up to the pole with a turnbuckle on it. And then put another turnbuckle on your 1/4" wire at top.

You want them separated so you can have stronger cable anchoring it without spending extra $$'s where its not needed.

The turnbuckles are essential because the wire will tend to stretch so you will have to tighten it through the year. The anchor may have to be tightened to keep the pole from twisting too much.

The main reason to use a single anchor is that its easier to get a tractor past. If you are only doing 1 row, I guess that isn't an issue.