[TowerTalk] Guy Rope Termination
n1lo at hotmail.com
Mon Feb 6 09:13:18 EST 2006
Manufacturers commonly use 20% of the breaking strength of rope as its SWL
(safe working load), but this isn't always the case. The manufacturer should
have no problem telling you what the actual breaking strength is, if it is
not marked on the spool or packaging. From there, you will have to estimate
what the strength of your application is, depending on knotting,
termination, shock loading, etc.
For the smaller ropes and cords, 1/4" dia and smaller, I cut them with
scissors and melt the ends with a lighter, as Steve mentioned. I typically
wait a few seconds for the fused portion to cool, and then I roll the ends
between my fingers.
For larger ropes, I first wrap the intended cut point with 2-3 wraps of
electrical tape. Then, I heat an old table knife (blunt edge, stainless
steel flatware knife) with a torch until it glows red-orange, and pass it
through the center of the tape wrap. This technique leaves you with
beautifully fused ends that aren't swollen into lumps.
For portable masts, I frequently use braided 3/16" or 1/4" polyester rope
and terminate it with properly dressed and tightened knots. As Jim
mentioned, you can pre-tie the knots and use carabiners. I like to use
'quick links', which are inexpensive single links of chain having screw
gates. These are commonly available in the hardware or boating section of
For a 45' temporary mast, supporting a modest antenna, and using the common
1/4" braided polyester from the department stores, you probably will never
see enough loading to break your rope.
At the mast end, I use a double-turn bowline, either tied to the mast guy
ring or attached using quicklinks. At the anchor end, I use the taut line
hitch knot, which gives you adjustable tension control. Tied properly, these
are very reliable knots!
The weak link, in my mind, is anwhere the rope passes around a sharp edge,
such as the holes in the typical sheet metal guy rings. That's where the
value of using a carabiner or quicklink comes in.
Some texts (check out the book 'On Rope', by Padgett and Smith) indicate
that the figure-eight knot is among the strongest and easiest to tie/untie.
However, is does use more rope. If you REALLY need to know the actual
breaking strength of a rope and knots, research similar books on the
subject, or perform your own tests.
I like to use pre-tied knots with quicklink terminations. I identify each
guy rope using a wrap of light colored tape, and a sharpie marker to
identify the guy and it's length. I connect the guys end-to-end and
stuff/flake then into plastic buckets for storage (not coiled!). I use a
marker to draw a simple diagram of the mast and guying scheme on the outside
of the container.
Prepared this way, even those unfamiliar with knots can be directed to erect
the masts without worry, such as at a field day event or portable special
event station setup.
For my 'bucket o ropes', in general use, I mark the rope's length and safe
working load in pounds at each free end. That way I can be confidently
evaluate the safety of using a particular rope for a job on a case-by-case
basis. On the outside of the bucket, I list what lengths are available
Hope this answers your concerns.
<<I'm putting together a 45 ' temporary mast package. I'm using the 4'
military surplus sections that it seems you see at every hamfest.
I've got 3/16" double braid Dacron rope for low stretch guys. Most of
the double layer rope I've used in the past was pretty finicky about
treating the cut end, both in terms of how the cut is made and
processed, and also the way it is looped and knotted on the D ring. The
big problem I've seen is unequal tension on the inner and outer weaves
leading to failure of one and the the other.
I emailed the manufacturer and they were surprisingly unhelpful, saying
in essence "use a hot knife, we only make it, we know nothing about
I'd like to engineer a solution rather than hack one. Starting with the
guys I want to be able to calculate the real guys strength. I'm
concerned that the terminations will end up being the weak points.
Can anybody out there point me in the right direction? I've googled
every way I can think of and don't seem to know the right terms.
Rich Osman, N1OZ mailto:n1oz at arrl.net >>
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