Author Topic: knot question for a market gardener  (Read 3417 times)

jerf

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knot question for a market gardener
« on: January 27, 2010, 12:06:10 PM »
I'm forever making structures that involve tensioning wires between posts (Raspberries/ runner beans etc). Previously, I have used steel wire and fasteners but I now have access to lots of 6mm polypropylene rope and I like the idea of using knots - this is where you come in! I know embarrassingly few knots (just discovered the Zeppelin today). I have 2 questions.

1. If I have say 2 scaffold posts set in the ground, 30' apart, 6' high, whats a nice knot to use when its in tension.

2. Again same as before with scaffold or 2" timber posts but not so well secured in the ground. But this time I need more tension in the wires so I have ground anchor bars 4 feet from the end of each posts. I need to be able to tension the rope between the posts and to be able to tension each rope from the anchor to the post. Ideally, I would like to use 1 piece of rope.

I have seen what I think is called the truckers hitch which makes use of mechanical advantage - is this the best one to use and how should I tie the end when I have tensioned it? It does look a bit untidy though. I think the one for guy ropes (sorry, I dont know the name) wont hold tension throughout the season but it looks a bit tidier?

Many thanks

Jeremy


DerekSmith

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Re: knot question for a market gardener
« Reply #1 on: January 27, 2010, 01:36:12 PM »
Hi Jeremy,

Welcome to the Forum and thanks for the interesting post.  If you are moving from steel wire to 6mm poly rope, then you are in for some surprises.  Poly rope is much more elastic and heavier (especially after rain / dew).

I use 10m long wire supports in my greenhouse for tomatoes - if I used 6mm poly, they would be on the floor on a hot day.  When steel wire became available to gardeners we moved to it in droves - there was a good reason as you will find if you 'make the move'.

For your option 2. if the support is going to be up all season long, then you are going to need to be able to retension as the rope 'relaxes' under load.  At one anchor, fix on with a simple bowline loop or the Myrtle loop, across the tops of your support poles (notch the tops), then use the Truckers to give you some tensioning heave. Fix the end with a slipped half hitch, because you will need to retension again as the rope relaxes.

Please keep in contact with your progress and experiences, especially any interesting discoveries.

Derek

roo

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Re: knot question for a market gardener
« Reply #2 on: January 27, 2010, 04:18:06 PM »
I'm forever making structures that involve tensioning wires between posts (Raspberries/ runner beans etc). Previously, I have used steel wire and fasteners but I now have access to lots of 6mm polypropylene rope and I like the idea of using knots - this is where you come in! I know embarrassingly few knots (just discovered the Zeppelin today). I have 2 questions.

1. If I have say 2 scaffold posts set in the ground, 30' apart, 6' high, whats a nice knot to use when its in tension.

Knot to use for... tensioning?  For a crossing knot?  A terminal hitch?  Some more info would be good.  You might look this over:

http://notableknotindex.webs.com/Versatackle.html

Quote
2. Again same as before with scaffold or 2" timber posts but not so well secured in the ground. But this time I need more tension in the wires so I have ground anchor bars 4 feet from the end of each posts. I need to be able to tension the rope between the posts and to be able to tension each rope from the anchor to the post. Ideally, I would like to use 1 piece of rope.

Wires?  What wires?  Where are they?  If you have lines going from the top of the posts to anchors in the ground for tension, I think it's a bit much to think that everything will be done by one rope.

Maybe pictures would help. 
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sharky

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Re: knot question for a market gardener
« Reply #3 on: January 28, 2010, 01:30:42 AM »
In answer to your question about how to tie off the trucker's hitch, I usually use two half hitches right at the end of the loop that is bearing the load. If you plan to make it easy to untie, put the second half hitch on a slip.

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jerf

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Re: knot question for a market gardener
« Reply #4 on: January 28, 2010, 11:25:23 AM »
Many thanks for all your replies.
Derek, you have me worried that I will be having to re tension throughout the summer which I can honestly do without. I will only try it with a few structures this year. Perhaps the temps outside rather than in a greenhouse wont be enough to soften the rope too much? And yes, the support will be up all seasons and hopefully for a number of years.

You mention only one tensioning knot. I thought I would need 3 tensioning knots as the tension in the top cross rope (sorry, I called it wires earlier) will be less than then "guy ropes" as  these 2 will be working at 45 degree angles to the post as opposed to 90 degrees. Obviously, this would mean fixing the ropes to the posts rather than running over the top in a groove.

Ideally, I dont want any side forces on the posts so the ropes do all the work.

I agree, having 3 truckers hitches would be unpractical to do from one piece of rope so I will assume I need 3 pieces of rope?



Myrtle loop is a new one for me and I can see myself using it. If possible, I would like to be able to tension the truckers hitch from the posts/end of the row, as it will be difficult to get in to the main cross rope as it will hopefully be full of growth

That versatackle looks interesting for extra tensioning.I'll see how I get on with the truckers first and move over to that one if its hard work.

I think I have all the info I need to get started. I'll post some results once I have the posts in the ground.

Here is some pics of the idea:

Side view
http://www.photobox.co.uk/my/photo/full?photo_id=650570671

top view
http://www.photobox.co.uk/my/photo/full?photo_id=650570677

general idea but I want to use extra guy ropes to support lateral movement
http://www.photobox.co.uk/my/photo/full?photo_id=650570654

thanks again

Jeremy


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Re: knot question for a market gardener
« Reply #5 on: January 28, 2010, 04:28:50 PM »
It's not only that the rope gets longer with load and over time, but also its exposure to light. Anything starting with poly- is sensitive to light, and sunlight makes it brittle.
If it is supposed to be expendable, maybe it's not an issue, but I think galvanised iron might work  better.
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jerf

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Re: knot question for a market gardener
« Reply #6 on: January 28, 2010, 05:54:20 PM »
Yes, I forgot about the sunlight. I have so much of this rope I need a use for it and it's so much easier to store once its been used then steel and join together if needs be. On the other hand, if it breaks mid season with the bushed fully laden with fruit, I could loose the lot and some of next years to boot.

I'll tread cautiously

Thanks again

Jeremy

 

Dan_Lehman

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Re: knot question for a market gardener
« Reply #7 on: January 28, 2010, 09:12:59 PM »
... exposure to light. Anything starting with poly- is sensitive to light, and sunlight makes it brittle.

YMMV:  I have some fat 1/4" polypropylene rope outside now for some many
(six?) years, and it (a) wasn't new when I salvaged it (beach-combing --
exercise for the curious; and if golf is a sport, so too BC!) and (b) looks
none the worse for the exposure.  => black, smushed-oval (vs. round)
monofilaments.  In Commercial Fishing cordage I see much PP that looks
pretty good -- black is prevalent, also yellow, and orange for some used
in a kernmantle (my def.) form.
Which, yes, is quite a contrast to bits one can find where (a) much
is missing, embrittled to splintery bits, and (b) what remains is but
a quite pale imitation of the original -- comically, some former
yellow(2strands)&black(1) laid rope 1/4" sapling guy line with now
just whitish remains of 2 strands and the lone black doing the work!

But, to the point:  there seems to be some fairly effective means of
mitigating UV's deteriorating effects on (esp.) PP, and you just have
to get the good stuff!  Of what I've seen of the CoEx PP/PE cordage,
it resists (allegedly better than PP -- of PP of SOME quality) UV, and
in demise isn't stiff so much as powdery, having been flat-fibered.
-- small consolation re use & strength, but at least less a pain in
the hands (but maybe less readily observed & retired!).
(Recall I posted here a photo of some most peculiar yellow PP of
a ladder hoist line:  ONE strand was well embrittled & splintering;
the other two very little so!?  -- that's mystery to me.)

 - - - - - - -

Re the tying & structure, I'd think that you might need a support in
the center of your 30' span.  The loser end posts could work to some
advantage if set with some incline towards center span, anticipating
then subsequent adjustment tightening at the anchor-post spans
which will tend to bring them more upright.

Yes, some variation of a Trucker's Hitch can work.  Beware that what
you get in this with cordage sheaves (as opposed to some bits of
metal for less friction, or --best-- a pulley) is more good hold of the
tightening your surge of effort hauling puts in than actual mechanical
advantage -- which you DO get some of, but well less than what is
theoretically there.  (The Truckers is theoretically 3:1, but actually
more like 1.5:1.)

And you seen the point of the aforementioned "incline to center":
tightening this from the ends will bring the posts along with the
rope (friction) and so not need to overcome that friction to pass
rope to the hauling end (so much).  -- otherwise, one will have
to overcome the friction over the tops of the posts (if one is
running the line merely over the top).

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Andy

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Re: knot question for a market gardener
« Reply #8 on: January 29, 2010, 03:56:25 AM »

Hi Jerf,

Regarding the various versions of the truckie's hitch, I thought I'd plug the "quickie truckie", a version I learned used while doing garbage collection and constantly having to tie and untie bins to the back of a truck. Easier to undo than some other versions. If you know it you love it. :)

Warm wishes,

Andy
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