I met a guy this past summer whose 70 foot crankup US Tower come down ALL AT
ONCE. Essentially nothing survived except a couple antennas with bent
elements. I asked him if he had looked at the cable at the point where it
broke and what it looked like. His description convinced me that the cable
had suffered damage from resting on the same point, the sheave, at all
times.
With a crankup tower, the cable is certainly a single point where failure
leads to a catastrophe.
Applying some of K7LXC's magic lube (or equivalent) to the cable from time
to time certainly looks like good insurance. As would figuring out just
where the point in the cable is where it sits on the sheave with the tower
extended and carefully monitoring it for signs of compression. At this
point there is only a short piece of cable that is both taking the full load
and under tension AND compression. Everywhere else the cable is only under
tension. And tension is exactly what the cable is designed to withstand.
With a 3 section tower, there is only one point to monitor. I don't know
how 4 or 5 section towers do it but suspect there is also one point. But
maybe the fixed cable(s) that lift the upper section(s) also have a similar
single point failure possibility.
I hate single point failures, hi.
Jim/N1NK
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