[Towertalk] Pinning Mast to Rotator

[k4oj]

I suspect what would have "given" would have been the boom, Bruce - when 
there is enough torque to spin the beam loose independant of the rotor 
then it turns in one of two places - the boom to mast clamp or at the 
rotor.  I don't think you mentioned your boom to mast location slipping 
so since it is not pinned (I assume you would not put think of putting a 
hole in the mast above the top plate) that  was successful at holding 
the yagi in place - which the rotator's clamping did not.

IF the mast were pinned at the rotor and that force had no where to go 
then I suspect the boom would have fallen victim to the winds... pinning 
the beam kind of tempts fate.  You may wish to make the grip on the mast 
better by some of the tricks I have seen  posted here on Towertlk such 
as adding a piece of abrasive paper to the outside of the mast.  

Don't know whose rotator you are using, but I have often wondered the 
following:

The downside of Hygains approach is that the mast is held by that plate 
which makes contact with the mast along two small lines of contact area 
- seems like a saddle type arangement with surface contact over a wide 
area would give a better capture of the mast... this is the argument 
made for using saddles with u-bolts so seems it would be the same 
physics here!

IMHO the ultimate remake of the Hygain would be a cast bluck which has a 
plowed U-shaped groove down its length that is half of a 2" diameter 
masts OD (purists will note the HyGain people in all their wisdom 
designed the antenna for a 2 1/16" OD mast - guess the were counting on 
a coating of  some sort 1/32 thick being applied to a 2" OD tube). 
 Anyhow, this block with a plow running the length of it would afford 
surface contact over a very large area of the mast - it could be 
designed to have bolt holes that align with those on the rotor (5/16 for 
Tailtwister) and both U-Bolts with a very long leg or long machine bolts 
would take the place of the stock U-Bolts.  This would create a very 
large surface contact area.  

Then I wake up - and find out what it costs to produce something - even 
this simple - for amateur radio usage!

Happy trails, hopefully the storms are gone for the year!

73,

Jim, K4OJ




Bruce B. Sawyer wrote:

>I'm now in the process of repairing the damage to my antennas caused by
>Hurricane Lili a couple of weeks ago.  Little Cayman took a direct hit from
>that one, so my little antenna farm took quite a beating.  Among other
>things, the mast on one of my antennas was twisted around about 100 degrees
>in the rotator mount.  There was only one antenna on it--a Bencher Skyhawk,
>which is supposed to be wind-balanced.  I was just about to go drill a
>through-hole in the mast so I can put a bolt in and pin it to the mast when
>I started wondering about the wisdom of doing that, and wonder if others
>with more experience of taking towers through hurricane force winds have
>thoughts on the subject.  Had the mast been pinned to the rotator when Lili
>struck, the yield point likely would not have been the mast-to-rotator
>connection.  With a large enough moment, I wonder what would have yielded.
>The top section of my Rohn 45 tower?  The U-bolts on the rotator plate?  The
>rotator itself?  Whatever would have been forced to yield, I'm certain it
>would have been more time-consuming to fix, and obviously more expensive,
>than repositioning the mast in the rotator.  On the other hand, maybe it
>would be that nothing would have yielded, and now I'd have one less repair
>item on my to-do list.
>
>Thoughts?
>
>Bruce, ZF2NT
>Little Cayman Island
>
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