In a message dated 7/9/01 4:04:02 PM Pacific Daylight Time, djl@andlev.com
writes:
> But back to the question at hand. Suppose that you
> had a 72' tower, and you wanted to install a 24'
> chrome-moly mast (~18 feet sticking out) and three
> antennas. How would you do it?
>
> Seems to me that there are three obvious approaches:
>
> 1) Use the crane to do it all. Upsides: fast.
Also safe.
> Downsides: the antennas have to be ready when the
> tower goes up,
Well then, that's your goal - have *everything* ready when the crane
arrives.
> someone has to ride the crane to bolt on the antennas,
What I do is to have the crane guy bring a man-basket. I use my 6' nylon
slings to sling the boom and suspend the antenna from the hook at my waist
level. When you arrive at the top of the mast, then you bolt everything in
place. You only need the man-basket for the top antenna since everything else
can be done from the top of the tower.
> the crane has to be taller (~90'
> reach instead of ~50' reach since it now has to reach
> to top of the mast, not just above the center of
> gravity of the tower),
Even "little" crane/boomtrucks commonly have 90' of boom - be sure to
tell your crane guy how much you need.
It only has to clear the top of the tower (72') and a little more than
1/2 the mast length (approximately 13') so 90' or so of boom is about right.
> expensive (additional crane time, bigger crane), not reproducible for
maintence.
That's another topic. If you need to get at the top antenna you can
either climb the mast with temporary steps or lower the mast.
>
> 2) Pre-install the mast in the tower, raise the whole thing with the
crane,
> then install steps on the mast
> and climb the mast to install the antennas using a
> rope and pulley to raise them. Upsides: cheaper,
> reproducible for maintenence, antennas go on
> whenever.
Why waste your skyhook by not installing the antennas whilst it's there?
Simple, safe, quick and you're done.
> Downsides: someone has to climb the mast
> and work while perched on it (that someone would be me :-).
>
The number of people who can actually perform this manuever is *really
small*. If you haven't done it before, my guess is that you'll prefer not to
climb the mast.
> 3) Use two thrust bearings or similar, install the
> mast in the tower with ~3' sticking out pre-raising
> of the tower. Once the tower is up, climb the tower,
> install the top antenna, winch the mast up a few
> feet, install the next antenna, winch the mast up a
> few feet, install the next antenna, etc. Upsides:
> All of those of #2 above, plus no climbing of the
> spindly 2" mast. Downsides: Mechanical issues of
> keeping the mast vertical while installing the
> antennas (before it is seated in the rotor at the
> end).
This is a tedious job and will probably take 10 times longer than using
the crane (30 minutes vs. 5 hours). Go with the skyhook and he'll be out of
there in a couple of hours and you'll be done.
Cheers, Steve K7LXC
Tower Tech
List Sponsor: Are you thinking about installing a tower this summer? Call us
for information on our fabulous Trylon Titan self-supporting towers - up to
96-feet for less than $2000! at 888-833-3104 <A
HREF="http://www.ChampionRadio.com";>
www.ChampionRadio.com</A>
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|