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[TowerTalk] antenna location for hurricane

To: <>
Subject: [TowerTalk] antenna location for hurricane
From: "Jim Thomson" <>
Date: Thu, 25 Aug 2011 22:58:42 -0700
List-post: <">>
Date: Thu, 25 Aug 2011 20:05:56 -0400 (EDT)
Subject: Re: [TowerTalk] antenna location for hurricane
In a message dated 8/25/2011 2:49:07 P.M. Pacific Daylight Time, writes:

>  I hope for the best, but I don't believe that this  antenna will survive 
95 mph wind gusts...

Regardless of the potential  or real wind effects, I would suggest making 
sure your homeowner's/renter's  insurance is paid up. Everything else is 
mostly out of your control.
Cheers & GL,
Steve    K7LXC

## impact PRESSURE goes up to the SQUARE  of the wind velocity !   A 100 mph 
is 400%  more than a 50 mph gust.    At 111.8 mph, it's  500% more !   Forget 
average wind speed for a moment.  It's the gusts that will bust things apart.  
You only need
a gust to last a few seconds to do severe damage, and most gusts  last  from 
10-30 seconds.  

##  Hope you folks have invested in a good  quality, heat treated  4130 
chromolly mast, [104-120 ksi yield strength]
 or a  1026/1027 DOM mast  [75-90 ksi yield strength].   Trying to remove a 
bent mast, after the fact, is extremely 
dangerous at the best of times, esp if a crane can't be brought to the site.    

## Most of these commercially  made yagi's I see have poor mast torque 
compensation.  And when you see the typ  torque
numbers, like F-12 ants..... they are for a 70 mph wind.   In a 100 mph wind, 
those same  mast torque numbers  will
DOUBLE.  Reducing mast torque to almost zero is easy to do.   Either a torque 
comp plate is used at the short end of the boom,
typ the REF  end of the boom.
Or  equal portions of boom are on either side of the mast, and the light end 
has a counterweight stuffed into it, and secured. 

##  100 mph gusts are not something to trifle with.  Glass will break @ 100 
mph.   I'd suggest taping window's, secure everything in site. 
High winds like that will make mincemeat of tree's.  A buddy lost his tower 
last spring, cuz a tree [ with a poor root system]  came down
on his  3/8" polygon guy wires, slicing the top 2 x guys wires, then the bolt 
in the rohn equalizer plate sheared off.   The top 30' of the tree had
sliced through the bottom 30' of the guy wires,  just before the polygon guys  
morphed into the EHS steel cables.   Distance from base of tree to 
base of  tower was  >210'.   A paltry 52 mph gust brought down the tree. 

later....Jim  VE7RF  


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