Remember that nylon rope fatigues under stress, that's why climbers replace
their ropes after a hard fall. I'm not sure how much stress (dynamic load)
the first haul placed on your rope, but your breaking strength is probably
somewhere below the 4,500 pounds listed and working strength also reduced.
We also figure that a knot will reduce the breaking strength of a new rope
by 30 to 50 percent due to the stress of making all those bends.
>From: "Dick Green WC1M" <email@example.com>
>To: "'Dennis OConnor'" <firstname.lastname@example.org>,<email@example.com>
>Subject: Re: [TowerTalk] Tram rope
>Date: Mon, 18 Dec 2006 13:56:39 -0500
>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 my
>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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