[UK-CONTEST] Mastrant ropes - Caution?

[G3RAU at aol.com]

Thanks Keith,
The  80ft HD Versatower max head load at 120 mph is 9.9 sq ft or 0.92  sq m 
which equates to 102.6Kg. That is for mfrs recommended guying, which is  
supposed to be at levels 1 2 & 4, rather than 2, 3 & 4.  How much  that 
difference is irrelevant I don't know.  The normal failure bend point  is the 
bottom of the 3rd section, but your guying has moved it to the top  section it 
would seem.  Either way it is still wrecked .......
 
The standard Versatower supplied upper steel guy ropes were 7/19  5 mm  
with a SWL of 350 Kg.   The Mastrant D12 product has a SWL of 2040  Kg.  Miles 
higher.  The elongation of  D10 or D12 is 1.2% ,  whereas steel has roughly 
half that stretch.
 
Don G3BJ has put his finger exactly on the problem. Dynamic load. The  
increase of static load due to acceleration.  The rope is elastic so it can  
oscillate, which in turn increases the rate of acceleration, and so on until  
something gives up.
 
 The text books have formula to calculate all this. It is  complicated. You 
might assume that a rope with a SWL of 2040 KG and a stretch of  1.2% at 
that load would only stretch a proportionate amount when only loaded to  350 
Kg. This is Don's point I believe, is it correct to assume stretch is  
linear, and when you  dig even deeper  you have to differentiate  between static 
and dynamic loading.  The practical answer, without any  mathematics but 
clear physical evidence, is that the product stretches too much  and it was not 
fit for purpose.  A rigid tower rather than a  Versatower is quite a 
different animal, but we are talking specifically about  guying telescopic 
Versatowers.
 
So it appears the answer is you were sold the wrong product. The  product 
you used,  D12, has a SWL of 2040 Kg and sounds more than strong  enough, but 
that stretch of 1.2% is fatal on a Versatower, it can just oscillate  the 
tower to death. (Slack guys of any sort can achieve the same effect  though!) 
 
The correct product is actually half the price and is Mastrant D F1/F2  
which  is designed for movement like yachts rigging, hence it comes in  bright 
colours.    The stretch is roughly  the same as  steel at 0.54% i.e. only 
45% of the stretch of D12. It is much  stronger and so a 4 mm rope will 
suffice rather than 12 mm.  Far less  visible and more neighbour friendly.    4 mm 
has a SWL of  510 KG which is stronger than the mfr's recommended steel 
guys, and actually  costs less than half the price of the wrong stuff you were 
sold.........That  appears to be the correct product - at least on paper.
 
Whoever recommended D10 or D12 would appear to have been  inexperienced, it 
may be as strong as hell, but was unsuitable  for your  purpose due to its 
high elasticity.  Big mechanical  structures are specialist and not for 
salesmen to guess at.
 
You have my sympathies Keith
 
73 Derek G3RAU
p.s. has anybody tried using Mastrant F1/F2 , and how did it  behave?