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> From: "dave@egh.com" <dave@egh.com>
> To: TOWERTALK@contesting.com
> Subject: re: Mast Strength
> (yadda, yadda, yadda deleted for brevity)
> Tower #1: 2 element Cushcraft 40 meter yagi at top of tower
> 4 element Cushcraft 20 meter yagi 7 feet above it
> mast is 2" schedule 80 water pipe
> tower height (without antennas) is 99 feet
>
> Tower #2: 5 element HyGain 10 meter yagi at top of tower
> 5 element HyGain 15 meter yagi 7 feet above it
> mast is 2" schedule 80 water pipe
> tower height (without antennas) is 83 feet
> (more brevity)
> There has never been any damage to any of my masts during these and
> numerous lesser storms of 40 or 50 MPH. Any ideas as to why not?
> 73, Dave Clemons K1VUT
Dave, the answer is:
You are very lucky.
Just because all the engineering numbers say something won't work, it
doesn't necessarily mean it will fail on the first occurence.
However, the long term expectation is for it to fail.
Water pipe, whatever schedule, is not a structural device; it is
designed as a transportation medium. You will not find structural
data (i.e. tensile strength) anywhere for it.
In the folly of my youth, I, too, installed water pipe masts in a
number of local installations (there wasn't much tower stuff
available then, and I was the local "expert"). Some were not
particularly stressed with hardware, but some were.
One bent about 30 degrees and had to be removed with a crane.
Fortunately, the owner is still a friend of mine. Mine developed a
slight bend before I replaced it with real mast. I consider myself
very lucky, as are you.
There are only two kinds of water pipe masts: those that have failed,
and those that are going to.
Do yourself a favor and start budgeting and designing for replacement
masts.
73, Rod N4SI
The DXer formerly known as N9AKE
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