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drift anchors

Purpose: To install a drift anchor that uses the force of the current to tension a guide line.

Application:
Used to avoid dangerous hydraulics at the base of cascades, or to provide safe horizontal exit from a hydraulic.

Make sure you have a lot of practice with guided rappels first. Drift anchors function on the same principle of guided rappels, but the tension of the guide is caused by the pull of the current on the bags as they hang over the edge of a cascade.

Rappeler using drift anchor as guide line


Step 1 - Determine rope allotments:
From the top of the waterfall, estimate the amount of rope neccessary to install the guide and leave the rope bag floating in the target area of the water, while allowing enough remaining rope to complete the rappel.

Rope enough to rap & reach current



Step 2 - Throwing the drift anchor:
Tie off the rope bag to the rope at the length determined to allow the rope bag to set in the current. Toss the rope bag into the current at the foot of the cascade or past it, whichever seems appropriate. Allow the the bag to drift into the place where it will create the strongest tension. This will frequently be just under the threshold of the following waterfall, but not to far over the edge. Bear in mind that you want to be able to easily retrieve the rope bag after the descent.
Throw drift anchor, add bags with zip



Step 3 - Adding ballast
If the tension on the guide line is insufficient, try ziplining additional bags down the guide line. Pot Shots work well for this but any open backpack or sack will do.

To ensure against your rope pulling through the anchor prematurely, consider tying off a bight of rope as shown.
  Descending on the guided rappel



Step 4 - Descending:
Fix the guide to the anchor. The leader threads the rappel strand into his descender, clips a tether from his belay loop to the guide line with a carabiner, and begins to rappel.

To ensure against either the guide or rappel strand pulling prematurely, leave the tie-off shown in step #3 in place.

The last canyoneer can reblock the rappel strand as shown (hopefully the guide line will be tensioned by the rest of the team, rather than the drift anchor, for the last descender).
Descending on the guided rappel



Step 4 - Arriving safely and rerigging:
The leader will attempt to weight the guide line delicately to steer himself away from the hazard and land safely clear of the hydraulic.

In instances where the hydraulic cannot be avoided, or where the drift anchor slips and drops the descender into the hazard, the guide line can still frequently be used by the leader as he swims to escape the hydraulic.

This is similar to instances where you expect to have to enter the hydraulic; the drift anchors are installed to provide an escape line by which you can swim & pull on the guide line to exit the hydraulic.

After safely arriving, the leader should rerig the system as a traditional guided rappel.

  Horizontal exit from pool, rerigging


 
 
 
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