[TowerTalk] Do tall crank-up towers really work?

[K7LXC@aol.com]

In a message dated 12/14/00 5:00:21 AM Pacific Standard Time, wz7i@arrl.net 
writes:

> My quite helpful local volunteer ARRL counsel has advised me not to attempt 
>  to get a variance for the 50' limit on towers on my 9 acre lot.  He 
>  strongly encourages the installation of a crank-up.
>  
>  I have always had serious reservations about these towers at the 70' to 
90' 
>  heights I would like to install.  I am concerned about the obvious issues:
>      * maintenance

    There isn't much maintenance required. The obvious ones are a good 
inspection a couple of times a year along with lubricating the cables. 

    While US Tower wants you to replace the cable and pulleys every three 
years (factory liability weasel clause), from a practical standpoint if there 
is no 'serious' rust (some surface rust is pretty common and not dangerous) 
and no broken strands then you're pretty much good to go. 

    The pulleys are less troublesome but a good idea is to paint a spot on 
each pulley so you can observe its operation as the tower and cables are 
moving. Also, when you replace the cables you should replace the pulleys.

    Cable manufacturer approved cable lubricant is available from <A 
HREF="www.championradio.com">www.championradio.com</A>. While cable failure 
is not unheard of, some of it can be attributed to improper operation 
(overloading, not watching it as it's being extended, etc.).

    Here are some tips to extend cable life: 1) exercise the cable at least 
once a month (that is, run it up and down a couple of times), 2) don't always 
have it stop at the same places - vary where it stops; that way the cables 
will be less likely to "take a set" which is a potential failure spot and 3) 
lubricate the cables twice a year. 

>      * safety

    The safety issues are climbing and working on the tower; i.e. you have to 
have the tower extended to work on the rotator. I always put some good-sized 
pipes under the bottom of each section and then gently lower the tower until 
they are resting on the pipes. That way in case of failure, they're only 
going to fall an inch or two at most. Note: most modern towers have 'positive 
pulldown'. If yours is an older tower that lacks this feature - BE REAL 
CAREFUL about climbing it. Read an old column of mine ("Up The Tower" in CQ 
Contest magazine) for two really sobering personal experiences of serious 
crank-up tower accidents.

>      * limited loading capacity

    Well, any tower has a 'limited loading capacity' - you get the right 
tower for your load and wind conditions. US Towers can provide PE stamped 
plans for many states and many windspeeds (albeit with reduced capacities or 
height).

>      * future availability of parts

    Since US Tower is the 800 pound gorilla, they've been around for years 
and I don't see any reason why they won't be around for years to come. But 
they are subject to business conditions like everyone else so there are no 
guarantees. Even if they go out of business, you can still get replacement 
cables and pulleys from industrial suppliers. 

>  I would think that if you stick a beam 89' up in the air in 70 mph wind 
>  with the play that has to be present in all of the moving parts, you are 
>  asking for problems.  

    Well, if the tower is rated for it, it's not that different than 90' of 
Rohn 25G in the same conditions. Granted, crank-ups are more complex 
mechanical devices but there are thousands in use every day and they have 
proven their ability to perform within their specs. A little PM and careful 
use will prevent just about any problems. 

>  Is my view naive?  Should I do something much more modest?

    If you've got the budget, don't want guy wires and your legal counsel 
recommends it, it's what you need. 

Cheers & GL,    Steve    K7LXC
Champion Radio Products
Tower Tech

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