[UK-CONTEST] Mastrant ropes - Caution?

[David Aslin]

Derek,
I have some 6mm D-F1 being delivered this week, for top guys on a 30m
mobile Versatower.  We'll see how it does...
While living in the US, I learned that a high proportion of tower
failures are due to insufficiently tightened guys.  The rule of thumb
was to tension to 10% of the breaking strain of the guy - and use a Loos
gauge to measure it.  That's quite a bit tighter than many I see;
perhaps that tension may be sufficient to reduce the oscillation.  Any
comments?  Anyone else want to comment on non-conducting guy
alternatives?
73
David G3WGN
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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?