Assuming the tower is good and not rusty junk, I think a crane will
do the job, but it will be a little tricky.
If this sounds a little more than you want to handle, then take it down
one piece at a time.
If you want to take it down with a crane, then here is how I would
I think you would be better off to grab one leg with a nylon lifting strap
about 50' up - assuming you have only tower and no antennas or rotors.
If you have anything on the tower then this won't work
Grab it right at a section joint - assuming they have grade 5 bolts not
hardware store junk. Pick the tower up off its mount by jacking the
bottom section apart. The crane can generate a lot of lift and side load
and binding if it is not exactly over the tower, so jacking it free is better.
Once you get it in the air, things get tricky. You want to lay the thing
down without damaging it.
You should have prepared a set of supports that are level, in line, and
will support the 70' of tower in at least in 4 places or more.
You want to start to get the tower horizontal by using a rope to pull
the base over as the crane slowly lowers the tower. You need to
get the base onto the end support with the tower at a 45 degree
angle or less, so you don't bend the bottom of the legs. Once the
base makes contact, then have the crane operator keep the cable
exactly vertical by booming or swinging as he lowers it the rest of
the way down.
By lifting part way down - almost 1/3 - you have limited the unsupported
span to 50' as you do with final lowering.
70' tower and 50' unsupported span is the max on Rohn 25 that I would
attempt with this technique.
If you do it gently you should be OK. If something slips and you jerk it,
it will buckle. Keep everyone clear.
I was not present, when they did it, but I was the beneficiary of a
commercial outfit attempting to take down 180' of 24" face tower this
way. They hooked onto it in two places and attempted to get it
horizontal before lowering it. It buckled very nicely in two places.
Lost two 20 ' sections, and bent the top star mount a bit, but
I got seven 20' sections and all hardware for hauling them away.
de n0yvy steve
Steven H. Sawyers PE
ARRL Volunteer Consulting Engineer
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