Razmere v gorah

RSS podatki
Vseh zadnjih 20 prispevkov
Iskanje po bazi podatkov

Novejši prispevki: (30)

Note 44.331 MOUNT-L 331 of 517 CUPIDO::STRITAR "Andrej Stritar,IJS,(61)-371-321" 95 lines 1-MAR-1994 08:19
CUPIDO::STRITAR "Andrej Stritar,IJS,(61)-371-321" 95 lines 1-MAR-1994 08:19
--------------------------------------------------------------------------------
From: STENAR::STENAR::MRGATE::"X400::1=de::2=d400::3=tr::5=EDU::4=METU::4=CC::4=VM::6=MOUNT-L" 2-FE
To: CUPIDO::STRITAR
CC:
Subj: Re: Rope strength

From: NAME: Mountaineering Discussion List MOUNT-L
FUNC: edu <6=MOUNT-L@4=VM@4=CC@4=METU@5=EDU@3=TR@2=D400@1=DE@X400@STENAR>
To: NAME: Multiple Recipients of
FUNC: edu <6=MOUNT-L@4=VM@4=CC@4=METU@5=EDU@3=TR@2=D400@1=DE@X400@STENAR>

RFC-822-HEADERS:
Comments: To: MOUNT-L@vm.cc.metu.edu.tr

Date: 02-Feb-1994
Posted-date: 02-Feb-1994

>
>
> A dynamic rope is not recommended for Z-drag systems. A rope such as the one
> you described is meant to hold falls for a lead climber. It has a limited
> number of "falls" for a life expectency. Since the Mammut rope you described
> is not intended for river rescue, it will perform poorly and likely with a
> short life expectency. A rope used in a z-drag should be designed to hold
> "heavy" loads for a long period of time, not a sudden heavy load for a short
> period of time asiin a "shock" situation.
>
> Another drawback that I find is that this rope will likely hold water and
> become very heavy--something I would not want in my boat!
>
> I am concerned that using a dynamic line like a Mammut 11mm for z-drags will
> over some unkown period of time result in a failure of the rope with the
> potential for injury--especially if used in a boat recovery under a heavy load
> (eg: 12 mph current creating an average total force of water on a swamped
boat
> of
> of 2688 pounds--without accounting for friction on the "pinning object").
>
> Marc Connolly
>

Sure, a dynamic rope is not designed for high static loads, but it
doesn't mean it will not work. Dynamic kernmantle climbing ropes
differ from static kernmanle ropes in that their core filiments are
twisted. This twist or spiral allows the rope to unwind some when a
heavy load is placed on it, which allows for stretch way beyond what
the filiments themselves can handle. The core filiments of a static
rope are straight so all the stretch is in the filiments. A high
quality dynamic rope will recover most of its core twist after the
load is removed. However each time the rope is loaded heavily, the
core will slowly loose its twist and the rope will loose its ability
to stretch. If a dynamic rope is repeated used for heavy loads its
core will completely untwist and it will basically be a static line.

If you really want to keep your lead climbing ropes in good shape, you
should never load them intentionally. Even rappeling and lowering
will reduce the stretching ability. I have seen many of mine and
friend's ropes lose a good bit of their stretching ability from just
rappel and TR use with no leader falls on them. A friend of mine has
a dynamic rope that now stretches less than static line. Needless to
say we don't use it for leading anymore.

Since dynamic rope's core is twisted and more loosely piled, there is
less filiment cross section in the same cross section of the rope as
compared with static rope. As such, the same outside diameter of
dynamic will have a lower tensile strength than static. For example,
11mm Bluewater static is rated at 6600lbs and 11mm dynamic 5000lbs.

Dynamic ropes can also be purchased with a dry treatment, which
greatly reduces the amount of water the rope soaks up. I haven't seen
any static rope sold with dry treatment and I don't know why (other
than cost). It would be great for caving. It's really a pain to pull
up a 600 foot rope that has doubled in weight because of the water it
has soaked up.

Anyway, for your Z-drag, I see no problem using a dynamic rope
provided that you use a sufficiently strong rope and you don't use
that rope ever again for climbing. If you really have 2688 lbs of
load on the rope (how can you come up with such an accurate number?)
and the application is not life critical you should be using at least
6000 lbs rope (IE 11mm static). If the application is life critical
with a 3000 lbs load (obviously not for your application) you had
better use double 5/8 (17mm) static. I recall the 5/8 as being 15000
lbs tensile strength.

Willie Hunt

PS

If you are really putting that kind of load on the ropes, you should
also be concerned about knot strength and any other bends. After
3000lbs is applied to a rope knot, it's almost impossible to untie.

---gora
18.222.117.109(0)
1143609 (639869,195,503545)
1105692 (619156,66,486470)
razmere.e-gora.si