Prusik cord length

So I bought a 6mm x30ft cord to cut down to make a friction hitch/third hand for rappelling, how long should I cut off, in order to tie a double fisherman’s and have an appropriate friction hitch length? 

5 feet ought to do it. I wouldn't go any shorter.

Yoda Jedi Knight wrote:

5 feet ought to do it. I wouldn't go any shorter.

+1

Tied with a double fisherman's you end up with a single runner length that can carry over your shoulder, tripled to carry as an alpine draw, or doubled and girth hitched to the back of your harness or knotted and hung from a biner on a gear loop.

4’ if it’s coming from your leg loop, 6’ if from belay 

I generally use a 5mm autoblock (not prussik) attached to either leg loop (if the ATC is in my belay loop) or belay loop (if the ATC is extended on knotted sling, PAS or Petzl-thingy). In both cases the autoblock is below the ATC. My ideal length for either is: the finished tied loop should be as long as the distance fron the tip of my outstretched index finger to the inner bend in my elbow. Don't cut the tail off until you have it right. Try it.

I don't know where these numbers are coming from, but you want a 4' length for your third hand, says the world of climbing retail. 

Nathan wrote:

I don't know where these numbers are coming from, but you want a 4' length for your third hand, says the world of climbing retail. 

From experience. You are right. 4 feet plus 1 foot for tying the knots.

27 inches after the knot is ideal for rappelling. You can always attach a separate sling to make it longer for other scenarios. 

Cam Brown wrote:

27 inches after the knot is ideal for rappelling. You can always attach a separate sling to make it longer for other scenarios. 

Agreed. If the loop is just for rappel backup, most of the suggestions are too long. The loop I use for rappel backup is 13 inches, so 27-28 inches of cord to tie it sounds about right. If you need to use it for anything else, you can always add slings to it.

Edited to add: 6mm is pretty thick. I use 5mm for third hand. You may need a longer loop in order to wrap around the rope enough times to get a good grip. Like suggested above by another poster, you can always tie it first with longer cord, adjust the length, then cut the excess.

For a friction hitch below the belay device, I like a 1ft loop (which takes ~3.5 ft of cord).

It's not that hard to tie the loop and experiment before cutting.  

A double fisherman's with 2" tails in 6mm cord uses about 15" of length. The Sterling Hollowblock and Beal Jammy loops are about 13.5" and 19". So, if you wanted to emulate those using 6mm cord 13.5 x 2 + 15 = 42" or 19 x 2 + 15 = 53".

Personally, I carry one short loop and tie my chalkbag on with 104" of untied 6mm cord. I fold the 104" in half and thread the bight through my chalkbag loops. I tie it around my waist using the untied ends to make a sheet bend in the bight. Adjustable and secure.

Leaving my chalkbag cord untied gives me plenty of options: I can tie it into one continuous loop. I can tie an overhand loop at one end for a Prusik and use the untied end for a Munter-mule. I can tie a loop at both ends and use one for a Prusik and the other for a foot loop. I can use it for rap tat.