It depends on the angle of the dangle, so to speak. The the copy of the
YCCC Scuttlebutt article at the top of the page at:
http://www.k1ttt.net/technote/tram.html for calculating forces. In the
examples I show that a 100# antenna can easily get over 500# tension on the
rope if you try to pull it too far out from the tower.
David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: email@example.com [mailto:towertalk-
> firstname.lastname@example.org] On Behalf Of Dick Green WC1M
> Sent: Monday, December 18, 2006 18:57
> To: 'Dennis OConnor'; email@example.com
> Subject: Re: [TowerTalk] Tram rope
> 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
> 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
> tram line will break?
> 73, Dick WC1M
> > -----Original Message-----
> > From: Dennis OConnor [mailto:firstname.lastname@example.org]
> > Sent: Monday, December 18, 2006 7:27 AM
> > To: email@example.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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