The ice season is nearing an end but for those still out and about please consider the
following:
It is well known that the ‘V-Thread’ or the ‘Abalokov’
anchor is a standard practice for rappelling ice climbs. These types of anchors
are used by most ice climbers these days.
I have seen quite a few ‘less than ideal’ methods and
materials used for this practice as of late.
Some issues:
1. Diameter of Cord- It is ideal to use a minimum of
7mm cord for these anchors. Thinner diameter cord can certainly hold body
weight but does not provide a very large safety margin. It should be known that
cord or webbing can loose a significant amount of strength once a rope or two
has been pulled through the cord. The pulling of the rappel rope through the
webbing or cord often melts into the sheath and core of the material. I have
seen many V-threads made with 5mm and even 4mm cord this year. I’m glad
these are working for whoever is using them but I surely wouldn’t recommend using V-threads with this
very thin material when you come along them on your decent. I climb
with many advocates of ‘light and fast’ climbing but the wt.
difference between 5mm cord and 7mm cord will not make or break your ability to
ascend ice climbs. I often use pieces of an old 8 or 9mm rope to leave on
climbs, which is stronger and takes longer to wear out than thinner cord and is
a good way to recycle old ropes.
2. Type of Knot- I see a lot of small diameter cord
used for V-threads tied together with a simple ‘overhand knot’.
The standard knot for connecting cord in V-threads is a ‘fisherman’s (Single or
double)’. The ‘overhand knot’ is popular for attaching (equal
diameter) rappel ropes but only with large amounts of tale (1.5 - 2 feet is
fine). Tests show that the ‘Overhand
knot’ can roll or flip
(essentially start to fail) more easily with icy or wet ropes, smaller diameter
cord, dissimilar sized cord, or with knots that aren’t properly dressed. The
cord within V-threads is often icy, thin, and large tails are not practical.
Again, this knot (the overhand) obviously works for many people in this
application but the safety margin is less and someday an accident will happen.
See http://www.needlesports.com/advice/abseilknots.htm
for some interesting ready on the ‘Overhand Knot’ for attaching
rappel ropes.
3. Spectra or Dyeenema slings- Many of us use these thinner, light
wt. sewn slings for ice and rock climbing (instead of bulkier and heavier
nylon slings). These light slings are especially nice for winter climbing as
they don’t absorb water the way that Nylon slings do. Ever notice that
you can’t buy webbing made with these materials off the spool like you
can Nylon? The reason for this is that the knot
holding strength of these materials is much less than with nylon. These materials are slippery and
the knots can easy slip and fail. I have seen several sewn Spectra slings that
have been cut and then re-tied around trees or used in V-threads. Don’t do this. If you are desperate than use your climbing rope. There is
‘cord’ (generally 5.5mm) made out of spectra as well. This too is
slippery. It is recommended to use a ‘Triple Fisherman’s’
knot when connecting this type of cord to prevent the slipping of the knot.
Remember to:
1. ALWAYS back up your V-threads or Abalokov anchors with an ice screw or
two while the first climber(s) go down. Make sure the back up is through the
rope and not simply through the anchor material in case the knot slips or cord
breaks. The last person to go can remove the back up screw knowing that the
V-thread has been tested.
2. It is good practice to go off of two V-threads, especially if you made
neither of them. I will go of one if I made it myself but will almost
always make another if there is just one old thread in place. Better safe than
sorry!
3. Try not to litter the ice climbs (especially popular ones) with V-threads
of poor quality, ie: marginal materials, they will only have to be backed up
with another.
4. When adding a V-thread to be combined with an existing thread make them
equalized so that both can be used. Having one thread a foot shorter than the
one below nearly pointless.