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Re: [TowerTalk] 90 ft erection

Subject: Re: [TowerTalk] 90 ft erection
From: "Richard (Rick) Karlquist" <>
Date: Fri, 07 Sep 2007 22:03:57 -0700
List-post: <> wrote:

> looks to me like a variation of the standard "falling derrick" method  I
> think it is called and yes, there are guys, 4 sets of them.   
> No, this is not a falling derrick. It is just a  tilt-up fixture pulling it 
> up. 
That is exactly right.
Having a fair amount of experience with the falling derrick, let me
point out that the advantage of the falling derrick over the raising
fixture is that you can pull on the tower in more than one place.
With the raising fixture you either have to attach low and risk the
top bending over, or attach high and lose leverage and thus
risk bending the raising fixture and/or buckling the tower.  If they had 
used the falling derrick method, they would be able to pull on all 4 
front guys at the same time and support the tower uniformly.

Another advantage of the falling derrick is that the "derrick" is
only under compression, not bending moment like the raising fixture.
And raising fixtures have been known to break (or their pulley assy).
I suspect people with only a casual understanding don't appreciate
the significant differences in the mechanics of these two methods.
OTOH, the most unpredictable hazard of the falling derrick is that
of the derrick buckling.  To prevent this, the derrick must be
stiff, not merely strong in compression.  The best thing is to use
additional tower sections as the derrick instead of a big pipe.
Nevertheless, you see a big pipe being used all the time.

As others have pointed out, you MUST have side guys in place.  I
won't venture an opinion whether they were or weren't in place
based on the low quality video.  Also, you must prevent overshoot.
If you let the tower continue past vertical, it can easily break
the hinge loose.  You need someone on the back guy to ease the
tower to vertical.

Rick N6RK

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