[UK-CONTEST] High Winds...Rope ?

[Clive Whelan]

Gentlemen

I would humbly suggest you do not use polypropylene rope for
guying. Its only advantage is that it is cheap, but its UV
resistance is poor and its abrasion resistance rather  poor
also.

 I'm puzzled that Bob finds it stretches as this is not a
known property of the material.  Polypropylene is rigid and
strong and is a good material for rods, bars and insulators
( although its RF properties are debatable), but not guys,
except in non demanding applications ( e.g. tents). Nylon
( polyamide) also has poor UV resistance and high elasticity
making it quite unsuitable for guys, although possibly
beneficial for halyards; in fact I have used polester ( see
below) for everything where financially viable. You might
have to pay as much per metre as you do for RG213 :-((

The generic material ( non metallic) for guys is polyester,
and this is the most expensive commonly available rope, as
may be seen by a trip to B&Q. There are then many types of
polyester formulated specifically for various purposes, and
Phillystran is  well known in the U.S. as a very good guy
material in respect of strength, U.V resistance etc. That
reputation is based largely on guyed freestanding towers,
which is a very demanding application. I have used "garden
variety" polyester rope for guying of masts over many years
with no difficulties and no need to replace ( caveat British
levels of U.V.!), and would suggest that it is also quite
suitable for restraining guys on crank up towers.

I am not an engineer , but I believe the strength will vary
as the square of the diameter, such that 8mm dia is four
times as strong as 4mm, but if I'm wrong somebody will no
doubt correct me.


73


Clive
GW3NJW
-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com]On Behalf Of Bob
Henderson
Sent: 12 January 2007 10:20
To: Adrian Rees; uk-contest at contesting.com
Subject: Re: [UK-CONTEST] High Winds...Rope ?


Hi Adrian

You say your biggest problem will be getting your towers up
or down in high
winds.  I assume you are talking about crank-up towers in
that case?

The first part of the above problem is easy to answer.  You
never attempt to
crank a tower up in high winds!  The answer to the second
part of this, is
that when you have crank-up towers you need to take steps to
be aware when
high winds are likely.  You then crank down your towers in
advance.  If you
get caught out and your towers are up while high winds are
developing and
the sections become locked together due to wind pressure
then you will need
the assistance of a second person if you are to stand a
chance of retracting
the towers.

Now to the issue of guying.

You should understand that crank-up towers are mostly NOT
designed to be
guyed in the way a fixed tower would be.  The accumulated
tensions in the
guy system translate into a downward force on the tower
itself for which it
is not designed.  Ignorring wind, this force is a dead
weight headload, all
of which would have to be supported on your tower cables.
This is not a
great idea, as it substantially reduces the usable headload
of the tower.
That said, the attachment of low tension guys for the
purposes of
stabilisation in modest wind conditions is of benefit and
this for two
reasons.

1. These will stop your towers from leaning uncomfortably
and looking untidy
in modest winds.

2. They provide a means by which a second person can assist
you in
retracting a jammed tower before the winds get high enough
to cause serious
damage.

I have used the same P80HD for 12 years now and it has
always been heavily
(over)loaded.  Currently it supports a F12 C31XR, a
Cushcraft XM240, a 5 ele
6m yagi  and an 80m delta loop, all on a very heavy 20ft
chrome molly mast.
All the above apart from the delta loop are rotated by an M2
Orion rotator.
I use 10mm polypropelene rope to add stability to the
system, providing the
benefits detailed in 1 & 2 above.  If it looks like it's
going to be
dangerously windy I retract the tower to about 45-50ft.

Yes the poly rope stretches.  That's ok for this purpose.
It's also not UV
stable over long periods.  I have to change mine every two
years here but we
see more sun than you do.

I hope this helps you with your planning.

73

Bob, 5B4AGN


----- Original Message -----
From: "Adrian Rees" <rees.a at btconnect.com>
To: <uk-contest at contesting.com>
Sent: Friday, January 12, 2007 9:48 AM
Subject: [UK-CONTEST] High Winds...Rope ?


> Hi all
> Well with the high winds we've been experiencing (my home
WX Station tells
> me gusts up to 91MPH) I've been thinking about what type
of rope I'll need
> to use to guy my towers.
> Steel or Stainless Steel would (I guess) be the strongest,
but that has
> the problem of Resonance (unless of course you break up
the lengths with
> insulators).
>
> Anyway, what suggestions does the list have for guy rope ?
>
> I have been looking at Phillystran, but wonder if a
cheaper-just-as-good
> version exists in the UK ? If so who supplies it ?
>
> As my QTH is on an exposed hill, its been pointed out that
my biggest
> problem will not be when the Towers are up or down. The
problem will be
> getting them up or down in high winds.
>
> Adrian MW1LCR
>
> _______________________________________________
> UK-Contest mailing list
> UK-Contest at contesting.com
> http://lists.contesting.com/mailman/listinfo/uk-contest
>

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