The prusik is an easy to tie knot that is generally used to provide
friction from a small loop of rope or cord that is attached to a longer rope
being used for climbing, rappelling, hauling etc. When the prusik knot is under
tension, it locks down on the main rope - when loose it slides easily along the
rope, providing a handy emergency brake for rappelling, a self belay line when
climbing or traversing fixed ropes, or an improvised ascending device. I use it
most often on unfamiliar alpine routes when I cant see if my rope will reach
the bottom - after I've rappelled far enough to confirm that my rope isn't
quite long enough, I tie a separate cord to create what's called a "Texas
Prusik" system to climb back up (this is easier than it sounds when you're
hanging there).
The prusik is listed as required "gear" for the Salomon WAR, and simply
consists of loop of accessory cord, that when tied, is not longer than your
arm's reach. I personally recommend a larger diameter accessory cord -
something in the 6 - 8 mm range, although cord as small as 4 mm will work. The
reason I prefer the larger diameter is the greater the difference in diameter
between your accessory cord and the rope you'll use it on, the tighter it will
grip, and with a larger cord you can more easily loosen the knot after its been
under a load, and slide and control your knot when underway.
Caution:
There is a lot of debate over the use of a prusik backup in rappelling
because although it can give some peace of mind to an inexperienced rappeller,
it can also create problems if you are inattentive. If you employ the backup -
you must always keep control of the prusik. If you let go of it, it will lock
into your rappel rope, and the only way to continue is to either unwieght the
knot so you can loosen it (tough to do if you can't reach out and touch the
wall), or cut the accessory cord loop (if you haven't got a knife you can
probably chew through it in about three days).
How to make your prusik backup...
You can purchase accessory cord at a local outfitter for about 35 cents
a foot. Ask for about 4 or 5 feet of 6 to 8 mm cord.
Start by tying your accessory cord into a loop (do this before race
day) with a double fisherman's knot (how-to by Ruckus
Society). If your loop is longer than the distance from your shoulder to
your finger tips - it's TOO LONG
For those with the bookMountaineering: Freedom of the Hills,
there is a good drawing of the system on page 172. For those without, Jeff
demonstrates step by step in photos in the following links.
Here Jeff has the routed the loop under the rappel rope keeping a small
bite of the cord in his right hand, and folded that bite back over the top of
the rope Step 1
He then pulls the free end of his accessory cord loop up through the
bite. Step 2
Next, he follows the cord loop with one more wrap and pulls the free
end once again through the bite Step 3
With the knot dressed down, he can clip the free end of his prusik into
a carabiner on his harness Step 4. If he does
this before he threads his rappel device, he can move around along the rope
freely by keeping the knot loose, yet if he slips the prusik will lock tight
(if the anchor point is a good distance from the edge - this keeps you safe
while moving to where you'll actually hook up). It is good practice to hook
your prusik into a carabiner other than the one that your rappel device will be
clipped into.
Here, Jeff is ready to go. He has his break hand (right hand) in the
slack position and uses his guide hand (left hand) to keep the knot loose
throughout his descent. Step 5 If at any time
Jeff lets go of the prusik, it will lock tight.
Here are some more views for tying the prusik knot itself from
Knot Knowledge
Variations: Add an extra wrap to thicker cords for more stopping power.
Some people choose to use a shorter cord loop and attach the knot below the
rappel device. I don't recommend setting it up that way, but if you do - ensure
that the cord isn't long enough to get sucked into your rappel device if you
lose control of it... because if it does, it will definitely slow down your
descent!
