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## Re: [TowerTalk] Sources for mast material

 To: , Re: [TowerTalk] Sources for mast material "Michael Fox \(K5MEF\)" Tue, 5 Aug 2008 18:04:07 -0700 mailto:towertalk@contesting.com>
 ```Hi Steve, We'll you're definitely the guy to know. To answer your question, the total wind load calculated in WinMARC is: Wind Speed Total 70 mph 6,151 in-lb 80 mph 8,197 in-lb 90 mph 10,243 in-lb 100 mph 12,290 in-lb My central question is the meaning of the "wind speed". The dialog box says "maximum wind speed expected". In my county, basic wind speed is 70 mph fastest mile, 85 mph 3-second gust. So I figured the max instantaneous is probably higher. So I figured 90 or 100 would be a good number. But it really depends on what the meaning of this number is in the MARC tool (fastest mile, 3-second gust, other). Can you define? Also, when the calculated total is 12,290 in-lb, the lightest suggested mast type shown in the list is a 40,000 in-lb yield strength. It's almost like it's looking for something that's at least 3X higher than the calculated total. Maybe you could shed some light on that too? Thanks in advance. 73, Michael - K5MEF -- We are what we repeatedly do. Excellence, then, is not a single act, but a habit. -- Aristotle _____ From: K7LXC@aol.com [mailto:K7LXC@aol.com] Sent: Tuesday, August 05, 2008 3:59 PM To: towertalk@contesting.com; k5mef@mefox.org Subject: Re: [TowerTalk] Sources for mast material In a message dated 8/5/2008 6:23:13 A.M. Pacific Daylight Time, towertalk-request@contesting.com writes: > I used Champion Radio's WinMARC tool to calculate the recommended masts for my planned VHF/UHF stack. If I enter an extra safe wind speed of 100 mph (my county is 70 mph basic speed), the tool suggests the following masts: Wall Yield Strength Description ---- -------------- ------------------------------------------ 0.120 40,000 6063-T835 Drawn aluminum tube 0.120 42,000 2024-T3 Drawn aluminum tube 0.120 46,000 A 500 Grade B Structural steel pipe 0.120 50,000 1010 Carbon steel CDBW Howdy -- What was the bending moment figure you're working with? 40,000 psi or what? This is much simpler IMO. Your 100 MPH safety factor has skewed the whole thing. That's 2-3 times the wind pressure as your REAL windspeed rating. I'll never discourage anyone from over-engineering something but you should back up a step or two. Your vhf/uhf stack is pretty small. If you lower the windspeed to 90 or even 80 - it'll change what's required - resulting in you saving a bunch of money and hassle. (I don't discourage anyone from spending money either.) All you really need is - dare I say it - some galvanized pipe; e.g. Schedule 40 water pipe, conduit, EMT, etc. It's rated around 35,000 psi yield strength which should be fine for your proposed installation. And you can drive down to your big box hardware store and get what you need. Cheap. Maybe you have some in your boneyard. While the galvanized pipe is 1.9" OD, your yagis won't know the difference. That's what I'd do. Cheers, Steve K7LXC TOWER TECH _____ Looking for a car that's sporty, fun and fits in your budget? Read reviews on AOL Autos. _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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