[TowerTalk] follow-up on 4-square conversion

[corneliuspaul at gmx.net]

Good point on the stretching of ropes.
I had to learn that lesson also when developing the spiderbeam

My advise would be to use 2-3mm diameter Kevlar (Aramid) rope.
This rope will have a breaking strength of around 200kg (2mm) to
350kg (3mm), so I guess it is strong enough.

On the other hand it is very lightweight, so even for long guy lines,
the slack in the rope will be quite small.

Kevlar has one of the best stretching values, it stretches maximum 2%, 
so your 85ft guy line might become 86ft long under stress.

Kevlar (Aramid) itself is not UV-resistant, therefore Kevlar ropes are 
normally made with a Polyester jacket woven around the Kevlar fibres.
This jacket effectively protects the fibres from the sun.


Good luck,
73s Con DF4SA





At 06:41 06.10.2003 -0400, Eric Scace K3NA wrote:
>Hi Dick --
>
>   Rope:  One of the problems with rope guys is that many kinds of rope are 
>quite stretchy.  The purpose of guying is to keep the
>aluminum tubing aligned in a column; this keeps downward forces (which can 
>be substantial) from collapsing the column (column
>failure).  To do this, any guy (rope or other material) needs to be 
>well-tensioned so that a sideways movement of the guy point
>doesn't merely take up the slack in the guy.
>
>   The total amount of stretch in material increases as the material is made 
>longer; i.e., elongation under a particular load add a
>certain percent to the overall length.  Long pieces of rope (e.g., the 85 
>feet needed to guy to the 60 ft level at a 45? angle) will
>therefore stretch more when the wind loads up the antenna (or a tree limb 
>falls on the guys).
>
>   Consider investing in low-stretch rope for at least the longest guys, 
>such as those with amarid fibers.  These are available at
>marine supply stores or, e.g., from New England Rope company.  Low-stretch 
>ropes are quite strong, so you will be able to use a
>smaller diameter rope.
>
>   The thinner the aluminum, the more important it is to have an adequate 
>number of low-stretch guys.
>
>   W1KM's approach to getting enough leverage to raise the antenna is an 
>excellent one.
>