John E. Cleeve wrote:
> Gentlemen,
>
> I would be grateful for constructive comment on the following problem. I am
> in the market for a couple of 100ft towers or masts, the problem is that in
> the UK there are very few manufacturers or suppliers, and those that can
> supply new, usually import their wares from abroad. However, one quotation I
> received from a UK manufacturer was for approximately 12000 GBP per mast
> (guyed), at the factory gate, carriage, guy anchorages and erection of the
> m
$20K plus! clearly, you're paying a lot for the labor, since the metal
cost is a tiny fraction of that.
What you get with a conventional lattice type tower is a tradeoff of
lower mass for more labor to build it. The lower mass buys you lower
material cost (which is a tiny fraction of overall cost), but more
importantly, the ability to erect a tall tower in pieces, by relatively
few people.
However, think differently..
Are you mass constrained? Particularly for erection? Do you have room to
assemble the entire mast on the ground before erection? Can you hire a
100 ft crane for, say, GBP1000 that can lift a few tons to 60 feet?
(assuming a slightly above midpoint "pick").
What about a suitable piece of iron/steel pipe (or, more properly, a
series of pieces of pipe of decreasing diameter). Or stacked telephone
poles?
Yes, it's not what most hams use, because a 20 foot section of 6"
diameter pipe weighs a LOT (about 600 lb).. you're hardly going to bring
it home on the car top, or lift it up with a couple helpers and the "iwo
jima" approach. However, particularly if you can find a surplus source
for the pipe. Scrap steel, is, I think, around $0.25/lb these days, so a
20 foot length of 6" pipe with 1/2" wall is going to set you back around
$150-200.. Call it a couple thousand dollars for 100 ft worth, by the
time you fabricate it.
Actually, I'd be looking around for aluminum irrigation tubing in large
diameters and use many tiers of guys. Around here, there's quite a bit
of it available, but that's because there's significant agriculture (I
live near the coastal plain in Southern California.. strawberry and sod
capital of the world, I think). I don't know if temporary irrigation is
something that is common in the UK (given that water falls from the sky
directly upon the plain beneath, and doesn't need to be carried for
hundreds of miles from the source)
It's possible, although tricky, to erect something like this without a
crane, but you're going to spend a lot of time and analysis figuring out
how to lift it without it buckling, probably involving truss and cable
stiffening. Think of sailboat (or sailing ship) masts.
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