On 6/8/2014 9:48 PM, Richard (Rick) Karlquist wrote:
On 6/8/2014 6:12 PM, Jim Lux wrote:
If you don't have heavy lifting gear, then the next thing is a falling
derrick rig and a suitable winch/come along/tow vehicle, etc. The
falling derrick helps insure that as your tower comes down past the 45
degree point, the load is still reasonable.
If you have 15-20 feet of suitable tower sections, you could probably
also rig up some sort of guyed vertical pole with a block and tackle
anchored at the top to help lay the other tower over.
The point on water pipe is well made, but pipe should never be used
where strength is involved. Yah, I know there's a lot of it in use, but
pipe is soft and bends far, far easier than structural steel tube of the
same size. It's also heavy for the strength. Tower sections are by far
the strongest for the weight, but you want the load on all legs, not
just two..
It shouldn't be used for masting either, but probably over half the
installations out there use it.
If pipe is used for a mast to give a big tribander a few more feet and
it bends, how do you get the antenna down?
We let one down yesterday (40' steel, not terribly heavy) from the W end
of my shop, with a novel approach, (N8ERFs idea. Thanks Dennis) at
least to me. There was a pulley at the top of the tower. We ran a rope
through a snatch block at the base, up through the pulley at the top and
back about a 100' to the SE to an anchor. There were also two guys held
by two hams. The rope ran NW from the pulley at the base of the tower
to three wraps snubbed around a 10" diameter Spruce tree. The guys at
the tree just slowly let the rope out while those to the SE helped keep
the load light.Other than a bit of a communications problem (the shop
was between the two groups so they could not see each other.)
73
Roger (K8RI)
A word of caution on the falling derrick method.
If you build a falling derrick to put a tower UP, the
first 6 inches are the most difficult. So it is
risk free to test the set up by raising the tower
6 inches and seeing if anything goes wrong. I
did this with my 50 ft Glen Martin tower and found
out that the derrick was well on the way to buckling.
Fortunately, I had the luxury of backing down and reinforcing the
derrick before trying again.
If you build a falling derrick to put a tower DOWN,
and didn't use it to put the tower up in the first
place, you have no way to test it. You might have
the tower within 10 feet of setting down and then
the derrick buckles or something. In your case,
it might be a one time use derrick, where you don't
want to waste money over designing it. Cut corners
at your own peril. Be sure to side guy the falling derrick.
Be careful. Borrowed tower sections are greatly preferred
over water pipe.
Very hard to predict when a pipe is
going to buckle.
Rick N6RK
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