[UK-CONTEST] Mastrant ropes - Caution?

[UKCONTEST]

Hi Derek

Your post was very interesting as a similar situation happend to me.

I use the Versatower spec guys, plastic covered steel.

Could you comment on Guy tension, and how to measure it, perhaps steel 
and the Mastrant stuff ?

This would be quite useful to know.

Thanks

Adrian MW1LCR

On 26/09/2012 22:16, G3RAU at aol.com wrote:
> 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?
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