The Autoblock is a friction knot used as a backup when abseiling.
The best part?
It grips the rope when loaded, and unlike other friction hitches, it can be released while still under load.
Let’s break it down.
Autoblock Knot Details
Type: Slide and Grip Knot
Other Names: French Prusik Knot
ABoK Reference: #505
How to Tie the Autoblock Knot
- Place the Prusik cord below the main line. Make sure you have a large loop on one side and a small loop on the other. Also, the Double Fisherman’s knot lies on the small loop and is slightly offset.
- Wrap the cord around the rope moving from bottom to top.
- Repeat it 3-4 times.
- Clip both loops into the carabiner.
Note: Always use most of the cord on the wraps. More wraps mean more friction. But if you use too many wraps, it may be difficult to slide the knot.
Autblock Knot Step by Step
To tie the Autoblock Knot, wrap the Prusik cord around the rope 4-5 times. Then, clip both the loops using the locking carabiner.
Finally, make sure all the wraps are neat and not crossed.
Rope Size
- Ideally, the diameter of the prusik cord should be no more than 70% of the main rope’s diameter.
- Example: for a 9mm main rope, a 6mm Prusik cord is enough.
- If both ropes are similar in size, the knot won’t grip well.
Pros & Cons
- Easy to tie and untie.
- Can be released under load.
- Can be loaded in both directions.
- Tends to slip when ascending.
Application and Uses
The Autoblock Knot is used as a backup knot when rappelling. It’s tied below the rappel device and clipped into the climber’s harness with a locking carabiner.
It slides down as the climbers rappel down. But in the event of a sudden drop, for example, from a rock fall, the knot jams and stops the descent.
It’s not recommended as a primary safety measure when ascending a rope.
Other Similar Friction Knots
Prusik Knot
The Prusik Knot is a classic friction hitch that is used to attach a cord around the main line, commonly used for ascending or descending the rope.
It can be used in both an upward and downward direction.
Klemheist Knot
The Klemheist Knot is similar to the Autoblock knot, except that in the last step, you feed one loop into the other rather than clipping both tails together.
Bachmann Knot
The Bachmann Knot uses a carabiner, which acts as a handle to shift the knot up and down the rope.
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