Good heavens, 50 ft of 2" Al is a totally trivial task for the falling
derrick method.
There are NO safety issues as long as everyone stays far enough away so
that nothing can fall on them.
A couple of Field Days ago I used the method to put up 40 ft of Delhi
(steel, triangular X-section with a face a bit bigger than Rohn 25) with
a TH3 tribander and Ham-M rotator on top as well as a 2m/70cm gain
vertical on top of that. I didn't use no stinking winch - totally
unnecessary. Just a haul rope from the top of the derrick. Everybody
stood around, (well clear) looking appropriately terrified as the 70 yr
old fart (me) pulled on the haul rope until the tower was vertical.
But, you gotta rig it right. I used 4 way guying which made it very
easy to set the guy lengths so that I only had to tie off the 4th guy
when it was up. 2 of the 4 guys were perpendicular to the derrick and
haul rope to keep the tower from slewing to the left or right as it came
up. They were under tension the whole time, including when the tower
was lying on the ground. Well, there might have been a tiny bit of
slack and I probably adjusted all 4 guys once it was up.
I also guyed the top of the derrick to the same guy anchors as the 2
perpendicular guys to keep the derrick from slewing to the left or right
as I pulled on the haul rope.
I also had 2 ropes from the derrick to the tower, one to near the top of
the tower and one about half way up.
I also ran a rope from the base of the tower to the guy anchor opposite
the derrick and haul rope so the tower base wouldn't skid towards me as
I started to pull it up. This was on a grassy field in a park so once
the thing started tilting up the base dug into the dirt.
The derrick was an industrial rated wooden 20 ft extension ladder with a
home fabricated clamp made from flat Al and some U bolts to fasten the
bottom rung of the ladder to one leg of the tower. This was the only
part of the whole thing about which I had some concern (and still do),
ladder rungs not being designed for this kind of loading.
This took quite a while to rig but only a couple of minutes to bring the
tower to vertical.
For your application I would think 20 ft of the same stuff the verticals
are made of would be fine for the derrick. A typical boom to mast clamp
made from some U bolts and Al or steel plate of reasonable thickness
ought to be fine for fastening the derrick to the verticals. Heck, a lot
of people would just walk the things up.
I suggest you have the XYL watch from a window a safe distance away as
you do the first one. Once she's seen how to do it, she could do the
other 3 while you yell encouragement as you quaff a couple of beer.
Hope this helps and good luck with your project.
73 de Jim Smith VE7FO
SJ W3TX wrote:
>Tommy,
>
>Another option is to use a bucket truck (if the location is
>appropriate...ie. no nearby power lines, etc).
>
>They can be rented very cheaply, and it eliminates all the need for the
>derrick hardware. Also eliminates the winch, which can be dangerous
>(freewheeling risk and cable snapback risk)
>
>I wasn't impressed with the safety of falling derrick when I tried it.
>Bucket truck is my recommendation.
>
>73, Scott W3TX
>
>
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