Fig. 1

The Theory

Tube or plate based belay devices create a braking force by making the rope kink round belay karabiner. Other things being equal, the more pronounced the kink, the greater the breaking force. Figures taken from an old Salewa information brochure quotes, Stitch Plate with one karabiner - 490lbs. Stitch Plate with two karabiners ( creating a more pronounced kink) - 880lbs.

Fig. 1 shows a Black Diamond ATC used normally. Note how the funnel shape of the ATC causes the rope to flare towards the belay karabiner, thus reducing the kink when locked.

Fig. 2 shows the same ATC used upside down,  narrow-end towards the belay karabiner. This constricts the rope towards the belay karabiner and causes a more pronounced kink, i.e. greater breaking force.

However, the problems with using the ATC in this way are:

• The keeper loop gets in the way.
• More important, there is NO keeper loop to stop the ATC from sliding up the rope.

Note: Click on the pictures for an enlargement ( 500kb)

Fig. 2

Fig. 3

Constructing a new keeper loop

1. You will need:

1. An old Black Diamond ATC
2. A length of 3mm cord
3. Some plastic tubing
4. Needle and thread ( not shown)

2. Carefully drill it out, lightly finish with a needle file and use the cord to tie a bowline loop.

Fig. 4

Fig. 5

3. Tie another bowline loop at the other end, with a length of about 10 cm. Make sure this loop is big enough to slip round your belay karabiner.

4. Trim and tidy up the ends with needle and thread.

Fig. 6

Fig. 7

5. Cut an appropriate length of plastic tubing and use the rest of the cord to pull the new keeper through.

Fig. 7 shows the modified ATC used in normal mode, suitable for 9 - 11 mm ropes. In Fig. 8, it is set up for higher friction, i.e. thinner ropes.

Fig. 8