[TowerTalk] Strongest mast material?

[Kurt Andress]

michael watts wrote:
> 
> So which mast is stronger:  Chromally or High Carbon
> Steel?  What is the general consensus on the strongest
> mast.  Double wall, triple wall?
> 
> I need 22 feet, 20 feet of which will be above the
> tower.
> 

Mike,

It can depend on what you get and where you get it. Regardless, you
should ask for and receive cert's from the vendor that provide the
minimum yield strength of the material run in that lot. 

With that, you can go design your mast. Thicker wall is always stronger
than thinner wall. Solid is stronger than tube, but not very efficient
from a weight and cost viewpoint. Often, bigger is better than thicker
from a mast only perspective, but bigger means more wind load on the
tower so one should consider that along with all the antenna loads.

Go to     www.ConsultPR.com    and click on the Ham Radio Connection in
the lower left corner of the home page. Then select the link for masts.
You will find a couple of published article reprints. Be aware that the
wind load calculations in the old NCJ article are a bit behind the
times.

What you suggest scares me. 
If what you envision requires a really strong mast, it could make for
some spectacular loads in the top of the tower and on the rotator.

Personally, I'd not be using such a short bury in the tower for a mast
that long unless it wasn't carrying very much antenna load or had been
analyzed and found compatible with the tower section capabilities. 

Rotator mfgr's usually don't publish their rotator lateral load
capabilities (a very important missing piece of information), so that
one is a crap shoot. You can be sure that if you have big time reactions
at the base of the mast, you'll want to understand how your rotator
carries these loads and carefully make your decision about what to do
with any kind of "thrust" bearing (if any at all) at the top. 

It would be a shame for you to spend good money on a strong enough mast,
only to ensure that it folded the top of your tower over, or caused the
rotator to rapidly go in the tank. 

-- 
73, Kurt, K7NV

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