[UK-CONTEST] Pulleys and rope
G3RIR
g3rir at yahoo.com
Tue Jul 10 08:34:20 EDT 2007
I may be called a pedant for this but
the method described and used by most groups is a FALLING DERRICK not a GIN
POLE.
A gin pole is one temporarily fixed to the top of a mast or tower or other
structure to lift other sections vertically.
We (DeMontfort University ARS) use marine grade pre-stretched polyester.
Polyprop even if used once or twice a year degrades with age even if not in
direct sunlight. Jimmy Green Marine Chandlery in Beer Devon has a good
website and mail order.
As for pulleys and blocks the same source has a multitude of choice. Cost
should not be an issue when safety matters and in any case you don't need
many even for a full open or multi-multi station.
Neil, G3RIR
-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com] On Behalf Of Chris Tran ZL1CT
Sent: 09 July 2007 22:37
To: steve at m0bpq.com; uk-contest at contesting.com
Subject: Re: [UK-CONTEST] Pulleys and rope
Hi Steve
As Adrian suggests, you will probably need a 'double-run' i.e. 2 pulleys at
the top and 2 at the bottom. There are several things to watch out for
though - for example, marine pulleys are expensive and often have a 'vee' on
one side which is designed to trap the rope when required - this is an
undesirable feature for antenna raising/lowering. Also, it is sometimes
difficult to obtain a pulley block which has an eyelet or hook at both
ends, which is what you will need for one of the pulleys.
For example, 2 x 20' steel scaffold poles with a 20m 3ele monoband yagi on
top are easily raised by one person using a 20' steel scaffold pole as the
gin pole, using 2 pulleys at the top and 2 at the bottom, with 10mm rope.
However it does take quite a time setting up the side guy tension etc. and
raising/lowering several times without the antenna of course.
73
Chris
GM3WOJ / ZL1CT
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