[TowerTalk] Installing a mast..same thread, different name
K1TTT at ARRL.NET
Sat Apr 20 09:21:41 EDT 2013
The problem most people have is that the pole is just barely tall enough,
especially on a tube top rohn top where you can't clamp the gin pole at the
very top. This means that if you can just get the pole lifted high enough
to get the bottom into the hole the mid point is pulled to the side so you
can't get the mast vertical to go into the hole... this requires someone to
get up high enough to grip the mast and push it sideways away from the gin
pole to get it vertical. If the pole doesn't flex enough you have to let
out some slack on the rope which means as soon as you push it over enough to
line up it takes a quick drop... this can be scary if you aren't ready for
it... you have to continue to let out rope to lower it causing more drops.
On flat tops this can also damage thrust bearings since every time it drops
down it get pulled sideways trying to cock the thrust bearing. This can be
helped by mounting the thrust bearing on the mast instead of the tower top,
this gives you a bigger hole to aim for and no problem lining it up... then
when the thrust bearing seats on the top you just lock it down.
David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
From: K8RI [mailto:K8RI-on-TowerTalk at tm.net]
Sent: Saturday, April 20, 2013 15:21
To: towertalk at contesting.com
Subject: [TowerTalk] Installing a mast..same thread, different name
I keep seeing references to not being able to install 20 ft mast with a gin
My question becomes...Why not. With a long enough gin pole and care it
should be easily accomplished.
First, the balance point is 10 feet from the end of the mast. It's not too
difficult to raise the mast from the balance point if two tag lines are
used. I prefer to attach just a foot above.
Second: Where are you mounting the pole?
It's typically on one leg of the tower, or on the face. If it's a clamp on
don't mount it above the last cross brace. That tower leg has very little
strength by itself and can easily be broken off.
So, let's say we have the top of the mount about 8" below the top of the
tower. It does have to clear the flat top plate which most of them do and
I'd add another 4" for the thrust bearing.
Lets say the pole extends 2 feet into the mount. It's 3 feet for some using
a double mount.
that means we have 2 feet + 8" +4"
+10 feet. or a 13' pole to raise a 20' mast at the balance point.
OR 14' for the one requiring 3' into the mount.
To raise a foot above the balance point would make it either 14 or 15 feet.
Measure your mounts for exact distances.
Trying to place the mount higher, or extend the mast higher *MAY* get you a
few more inches, but at the cost of safety.
If you have the mount(s) and the pole is not long enough, purchase a pole
that is. It may be a few bucks, but will save a lot of effort, grief, and
frustration. Of course get a good, strong alloy.
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