[UK-CONTEST] Mastrant ropes - Caution?

[G3RAU at aol.com]

In a message dated 27/09/2012 19:00:54 GMT Daylight Time, david at aslinvc.com 
 writes:

perhaps  that tension may be sufficient to reduce the oscillation.   Any
comments?


Be very careful doing that folks.  The design philosophy of a  60/80/100 
Versatower was to get the bottom section locked  in position with  tight guys. 
 (n.b. not the 85 or 120ft versions).  The top  sections could move + /- an 
inch or two sideways by design, hence the down  load on the individual  
section supporting cables would not be  increased unnecessarily.  The tighter 
the guys, the greater the download on  those supporting cables.  It just the 
same as increasing the headload, the  load is shared between the guys and a 
downwards thrust on the mast sections and  their supporting cables. 
 One easy solution would be to increase the diam of the supporting  cables 
from  5 to 6mm or more, but that defeats one of the design  objectives which 
was to use 6mm for the hoist cable and 5mm for the upper cables  on the 
bigger towers so that they broke first if there was a jam during  winching up.  
You would just get a softer partial collapse rather than the  whole lot 
coming down together and hitting the solid base stop.   Believe me it does work 
as a safety feature !
 
You need to do some maths before deciding on the optimum guy  tension, but 
basically you are right David.  Uprate the support cables  & hoist cable as 
necessary, increase guy tension by a controlled amount,  strengthen the guy 
anchors, and it should stay still enough not to rock a long  boom HF beam to 
pieces.  That is the theory at least..... HI! 
 
73
Derek G3RAU