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

[Dave Lawley]

5B4AGN wrote:

> 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 think this is highly misleading - the purpose of guys is to stop your 
tower toppling in high winds! This is borne out by the manufacturer's 
specification for a typical '80ft' tower as used in the UK. At 85mph 
wind speed an unguyed tower is specified to support a maximum of 5.2 sq 
ft of tubular aerial, but the same tower guyed will support 26.9 sq ft.

5mm wire rope is specified for raising the sections. This will support 
any reasonable headload at any practicable value of tension in the guy 
ropes. If you are concerned you could upgrade the wire rope to 6mm. You 
must pay attention to the condition of the wire ropes and this topic has 
been discussed before on this reflector.

Turning to practical experience, I have seen a 5-section trailer tower 
supporting a 204CD half way up on a sidemount, and a second 204CD at the 
top, rotatable. The wind got up, as it always seems to do on CQWW Phone 
weekend at the end of October, such that at times, two of the legs of 
the trailer lifted off the ground! It was the guys ropes (mainly 
polyester) which stopped the tower from toppling; we were not concerned 
about the load taken by the steel cables. In that situation attempting 
to lower the tower no matter how many helpers were present would have 
been more dangerous, but we had the comfort of knowing that the area 
downwind of the tower was clear so if it had failed - most likely due to 
guy stakes pulling out - damage would have been minimal. The tower survived.

I am not a qualified engineer and if you are in any doubt you should 
seek professional advice.

Dave G4BUO