Prussik knots

Swiftwater Rope Testing - Prussic Loop Strength

We wanted to find out how much those thin little prussic loops really hold, and which knots are best to use to keep them together.

We used brand new Powerloc Expert accessory cord from Edelrid with Diameters from 5mm to 8mm, knotted into a sling which was then tested to destruction on a rope testing machine. Both the Double fisherman's knot and the Overhand knot were used to make the sling as these are the two most common knots used to make prussic slings. The overhand knots were placed differently in the karabiner to see if this would make a difference to the strength of the sling.

Results: All slings were tested dry. Tiblock result is from Petzl.

Prussic Slings & Tiblock Strength

Prussic Loop Wet/Dry Knot Strength - kN
5mm Edelrid Powerloc Expert Sling
Dry
Double Fisherman
11.03
5mm Edelrid Powerloc Expert Sling
Dry
Overhand
6.70
5mm Edelrid Powerloc Expert Sling
Dry
Overhand
8.00
6mm Edelrid Powerloc Expert Sling
Dry
Double Fisherman
14.46
6mm Edelrid Powerloc Expert Sling
Dry
Overhand
9.34
6mm Edelrid Powerloc Expert Sling
Dry
Overhand
10.00
7mm Edelrid Powerloc Expert Sling
Dry
Double Fisherman
21.12
7mm Edelrid Powerloc Expert Sling
Dry
Overhand
11.61
7mm Edelrid Powerloc Expert Sling
Dry
Overhand
15.48
8mm Edelrid Powerloc Expert Sling
Dry
Double Fisherman
24.14
8mm Edelrid Powerloc Expert Sling
Dry
Overhand
14.91
8mm Edelrid Powerloc Expert Sling
Dry
Overhand
15.24
Petzl Tiblock
-
-
12

 

Conclusion: The best knot to use to make the strongest Prussic loop is the double fisherman's. All loops were a lot stronger than you would think.

Edelrid makes some of the strongest Asessory cord on the market. If you are using cord of a lower quality then results could well be much lower! For older / used / wet prussic slings the results could be much lower.

These tests were performed in cooperation with Axel Manz. Many thanks to Bonack for allowing us the use of their excellent testing facilities.