[TowerTalk] aluminum mast vs. tramming

[Roger (K8RI) on TT]

It depends on the tram, the mast, the tower, the tension on the tram 
line and back guy, and how much vertical load it adds to the tower.  
Tramming can cause a considerable increase in the vertical load. In this 
case calculate the total load on the 25G tower base.  Tower weight with 
all installed hardware and total down pressure from the guy lines at 
proper tension.  Then add the increased down pressure from the tram 
lines under proper tension. Then add the total weight of the new 
antenna.  Hopefully the total will be well less than the maximum 
vertical load for the tower.

It depends on the tram and how it hangs (mine is a two wheel version 
withe 4" wheels with the primary weight of the tram below the tram 
line.)  To me, the tram allows the entire antenna to be easily moved 
into position "sideways".  Just fasten the mast clamp.    Simply throw a 
light line over each end of the antenna with a man on each  to keep it 
level.  A well balanced antenna might not need this on a calm day, but a 
random light breeze makes it worth while.

If the Al mast (2" .25 Wall) is a tough alloy it should hold the tram 
well.  A back guy to the mast at the tram line would be a good idea, 
more for the tower than the mast Just try to stay within a few feet of 
the tower top albeit, high enough for the antenna to clear the tower but 
not get the elements in conflict with the higher antennas.  BTW the back 
guy reduces the side load on the mast making it less likely to bend

BTW,  that mast should be far stronger than a tower leg.  The legs by 
themselves are no where near the tower strength which gets most of its 
strength from all the parts working in concert.  Keep the tensions balanced.

I use 6061T6.  2 X 0.25.  I purchased about a dozen stock lengths (24'), 
over 10 years ago at one of the local metal supply places (Alro), mostly 
2" with the quarter inch wall along with some 1.5" and maybe 1.75".  
Wall thickness on those?  I'd have to check as I've used most of it over 
the years. There are now better alloys and tempers with some at lesser 
prices  Stock tube isn't as pretty as the polished stuff, but OTOH it's 
a whale of a lot cheaper.
NOTE Alro has a number of outlets around the country. I have no 
connection with Alro, just a satisfied customer.

73 es good luck,

Roger (K8RI)



On 3/12/2016 Saturday 8:18 PM, Steve K7AWB wrote:
>
> I have an aluminum mast  (which is 2” OD and 0.25” wall and about 11 feet) out of the flat top of the Rohn 25.  Already I have a M2 17-element 2-meter yagi at the top of the mast.  Below that antenna, and right above the flat top plate of the tower, I want to put my Force 12 5BA 5-band, 15 element yagi.
>
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> With my other tower, 90 feet of Rohn 45, we put up a 6-element Force 12 Mag 620 the first time by simply dropping each of guys and reconnecting once the antenna was above each guy point.  The second time we put it up, after balun replacement, we used a friend’s tram line and back-stay – of course the mast was 2” OD and 0.25“ wall and heavy!
>
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> I don’t think I want to chance the Rohn 25 at 102 feet with that drop-the-guy process.
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> So the question is : will a tram line work or will I bend the mast?  Even using a back-stay might cause undue pressure and bend the expensive mast.  And a bent mast does not rotate nicely.
>
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> Steve K7AWB
>
> Nine Mile Falls, WA
>
> DN17es
>
>
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>
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-- 

73

Roger (K8RI)


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