[TowerTalk] Tram rope

[Dick Green WC1M]

I don't want to be contrarian, but has anyone seen a tram line made of
reasonably strong rope break? Has anyone calculated the actual forces on the
tram line? For example, the breaking strength of 7/16" nylon rope is about
4,500 lbs, with a safe working load between 450 lbs and 900 lbs (some
references say no more that 1/5 breaking strength, others say no more than
1/10 breaking strength.) Would the forces exerted by a 100 lb antenna on a
tensioned tram line exceed that? Also, the haul rope supports some of the
weight of the antenna. Doesn't that figure into the equation as well?

I ask this question because yesterday I successfully trammed a 44 lb
Cushcraft 40-2CD to 110 feet using 7/16" 3-strand nylon rope. The next
antenna to be trammed is an 81 lb SteppIR. Is there really a chance that my
tram line will break?

73, Dick WC1M  

> -----Original Message-----
> From: Dennis OConnor [mailto:ad4hk2004 at yahoo.com] 
> Sent: Monday, December 18, 2006 7:27 AM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Tram rope
> 
> Let me second Dave's comment... Using rope for a tram line, 
> or small diameter cable is asking for a crash... I also use 
> only 1/4" EHS...  Because the tram line is pulled into a 
> caternary shape the total forces on it are far greater than 
> just the weight of the beam...
> The other thing I do is that the tram line is run up to the 
> top of the tower, through a pulley, and back down to a ground 
> anchor on the opposite side... This way the side thrust is 
> not transferred to the tower... Because of having to fly the 
> beam over the woods, etc., my tram line is 600 feet overall 
> and is kept on a drum and used only for that purpose.....
> 
> denny / k8do
> 
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