On 8/22/13 12:21 AM, Ray Benny wrote:
I'm in a dilemma.
I purchase a used TM-490 90 ft Sky Needle and recently found some of the
5/16", 7 X 19 aircraft cable lifting cable strands broken. The tower is on
the ground and not been in the vertical position for a number of years. The
problem, apparently there was some gas torch cutting done nearby and
splatter landed on the cable. This molten metal landed on the pull up cable
causing it to burn and sever 2 - 3 strands in one area, and another 3 - 4
strands 6 inches higher up the cable. The cable overall is otherwise in
very good condx with no wear marks. It might have been replaced prior and
the tower has been laying on the ground ever since?
The best and right thing to do is to replace the cable. But, I have been
going through my options:
#1 - Do the cable replacing myself. I have found the cable and cable
pulling grip for less that $200. The major problem is that this is a 3200
lbs tabular tower and not easy to move around. I would need to rent small
boom truck or forklift and some other misc working hardware to pull the
sections apart. It would not be easy, but feel I could do the job.
#2 - Hire someone to come here and do the job. This can run into a 4 - 5
thousand dollar cost.
#3 - Transport the tower to California and have it restring by the tower
company who made it long ago. I've checked commercial transport rates, r/t
shipment and cable replacement cost is more than option #2.
#4 - Do nothing and live with a few broken strands.
*At this point I am looking for thoughts, experiences and/or
semi-professional thoughts on option #4 - do nothing*. I've had a one
experienced tower person say that 6 - 8 broken strands out of 133 is
nothing.
Again, I know the proper/safe thing to do is replace the cable, but how
about doing nothing and using the tower as is?
What you really want to look at is: Am I willing to accept the cost of a
failure? if you are, then you can look to whether the chance of a
failure is low enough.
Let's compare a couple extreme scenarios.
In scenario 1, you got a really good deal(free) on the tower, you erect
it in the middle of an empty 160 acre field you own and if it were to
totally collapse in situ, your antenna and coax is a writeoff, but it's,
say, $500 worth of stuff. Your expense is that of cleaning up the mess
and the loss of $500. Heck, you can just leave it in a heap in the
middle of the field.
In scenario 2, your tower is mounted at great expense, including hiring
a crane to pick it up and lift it over your house to set it on the pad
in the middle of a crowded city lot, and you have $20,000 in microwave
antnenas, LNAs, and positioners mounted on it. You fought a long battle
with the zoning folks, the building and safety folks, and your neighbors
all said "that tower is going fail and cause the chickens in our
Williams-Sonoma coop to stop laying, our honey bees in our hive to stop
making honey, and that's after the electrosmog from your evil antennas
have caused our children to flunk out of school" A failure will strew
antenna parts in your neighbors yards, etc.
A failure in scenario 1 is sort of a non-issue. Put the tower up, don't
worry about the broken strands.
A failure in scenario 2 is a disaster. Hire an Engineer to supervise a
certified rigger, do proof testing on coupons of the cable they use, get
material certs on everything, keep all the paperwork in a safe place, etc.
I would assume you're somewhere in between. For most hams, who have
invested much time, and small money at any one time, accumulating their
equipment over many years, realistically, they're closer to scenario 1.
But the psychological trauma of seeing the destruction of that antenna
you bought with the money from your paper route in 1950s and have been
using for 60 years makes it seem more like scenario 2.
If you're carrying insurance, and looking to replace things that break
as the result of a failure, there may be a desire to be more objective
in the risk evaluation.
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