[UK-CONTEST] Versatower guy rope sizes
G3RAU at aol.com
G3RAU at aol.com
Tue Sep 13 03:11:52 PDT 2011
The Versatower recommended guying layout for a 60ft mast specified a 40ft
radius,
and the plastic covered galvanised steel guy ropes were 5mm 7/19 at the
top and
5mm 6/19 lower down. The D shackles and bottle screws were all 500KG
rating.
If non metallic ropes were specified Versatower supplied 10mm pre
stretched
black polyester.
In your case Alan I would most certainly not use a rope with a potential
100mm
stretch, the mast could get into a heavy rocking mode and destroy a big
boom
antenna due to the rocking motion which stretchy guys only serve to
exacerbate.
As you say, using a stronger rope means proportionally less stretch and
hence
less rocking, so that is the way to go. Guyed Versatowers were supposed
to
be able to move "an inch or two" at the top in order to prevent over
zealous guy
tightening producing excess stress on the internal lifting cables. How much
rocking you can tolerate depends on the antenna you are using, personally
I would get two people heaving on opposite top guys and keep tightening
them until no serious boom rocking of the antenna can be detected.
One solution is perhaps to make the top part of the guy synthetic where it
will
not upset the antenna radiation pattern, and make the lower part steel
which
stretches much less and is far more immune to damage. This method reduces
the overall stretch even more and may well prove economical, (but choose
a
non resonant length for the steel).
There is a lot of good design information about ropes & guying to be found
at
_www.mastrant.com_ (http://www.mastrant.com/) where you will find a
number of calculators to evaluate stress
and loadings on masts and guys, and some general advice.
73 Derek G3RAU
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