Introduction: Tying a Prussic Knot.

Picture of Tying a Prussic Knot.
A prussic knot is one that it tied with a loop of rope around a rope that is thicker than itself. typically is this means accessory cord (tied into a loop either using a double or single overhand knot or a fisherman's bend) commonly carried by climbers on their harnesses as part of a "rack".

It is tied around a climbing rope and allows the climber to ascend the rope, either by using another prussic loop, or by using a single prussic loop and a mechanical ascender, sometimes a belay devices is used in place of the mechanical ascender, if a belay device is used it will an "auto locking*" device.

  • auto locking belay devices may in some circumstances fail, for this reason it is important to have a fail safe, so that in the event the device fails, the climber does not hit the floor.

It is often used in the event where one climber is not able to complete a section of a climb, so the other climber proceeds to the top, and lowers the rope down so the second climber can ascend the rope and the two can carry on.

Step 1: The Way It Works.

Once complete and correctly tied the knot allows you to move it up and down the rope if you hold the knot itself to do this, but if you put load on the rest of the loop (the part that hangs down from the rope, it will lock solid, allowing you to put a foot in and stand in the loop, allowing you to move up. alternately it could be attached to your harness.

Step 2: Larks Foot.

Picture of Larks Foot.

The first part of the prussic is to tie a larks foot (also called a girth hitch). This is a very simple knot to tie indeed, and I'd be surprised if you haven't tied one before with or with out knowing it.

Because you are already tying this with a loop, all that you need to do is take part of the rope, and pass both strands between the loop, then pull down, and you have created a Larks foot.

As well as doing this with climbing rope, I have (as per request, always like to get feedback) re-shot some photos, with a carabiner and access cord. Whilst they are exactly the same thing, there is no point what so ever using this knot with a carabiner. It does give a better colour contrast which I think is the main issue.

Step 3: Turning a Larks Foot Into a Two Wrap Prussic.

Picture of Turning a Larks Foot Into a Two Wrap Prussic.

In this step widen the gap in the middle of the lark's foot. (refer to the first picture). This is a lot like retying the original larks foot except you are tying it through the middle.

Create a gap in the middle of the larks foot.

Pass the end through though the gap that you have created.

Tighten down and tidy it up if needs be.

I have reshot this sequence too, using the carabiner for clarity. Remember you want to be doing this with A rope rather than a biner, becuase well, this biner, even though one of the largest on the market is only 120MM high.

Step 4: Finish.

Picture of Finish.

Finally repeat step three, except with your two wrap prussic.

You can now move this knot up and down the rope by moving it up and down, but if you put force on the tail of it, the knot will clamp to the rope and will be stuck fast.


dchall8 (author)2008-08-25

Is there any way you could reshoot the pictures with contrasting colored rope? I lost you in step 2 and never recovered.

graeme.t.cooper (author)dchall82010-02-22

 this is also known in the rigging world as a triple sliding hitch.  It is the only knot allowed to secure a worker above a 3m (10 ft) hight. 

F1X0R (author)dchall82008-08-26

Sorry about that. but I don't think I have anything that would really contrast with it, like bright yellow! Climbing rope being rather expensive! Colour wise with the access cord it was a matter of "colours vary, get what your given." I will how ever endeavour to find or make an illustration of what it should look like to make it easier to understand. I will also try and reword it to see if that makes any difference. I think once you have the basic Larks foot the rest is pretty self evident though because you actually repeat what you just did. In effect you tie a larks foot with in a larks foot.

shrimps (author)2009-08-13

It's worth noting for future users that prussiks are a complicated business. And more importantly, that they can and do slip. Avoid ever only being attached to a single prussik. There are many different prussiks knots which all work slightly differently and are better for different roles. Also the ratio of the diameter of the prussik cord and the rope it is being used on greatly affects the amount of friction generated. Thinner cord will bite more, fatter cord will slide more. Choosing the number of turns in a prussik requires experience to judge correctly. Getting it wrong can create a prussik which grips so hard that it is impossible to move, or one which is so loose that it fails to grip at all. Finally make sure the used to tie the two ends to create the loop for your prussik is sound. The author didn't cover that, and a well tied prussik won't help you if your loop opens.

floydfan1 (author)2009-03-05

So glad I found this site. I am a hunter and needed a way safetly up and down the trees that I hunt from, this is perfect than you.

CaseyCase (author)2008-08-26

Learned this knot after seeing Roger Moore ascend a rope with his shoelaces in a James Bond movie. Wondered, "how did he do that." Curosity can be powerful!

F1X0R (author)CaseyCase2008-08-27

Could be done, if the laces were strong enough! Though they may be a bit short.

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