Double fisherman’s vs. overhand rethread
Tying Prusik loops with a bend for your Prusik Minding Pulley
For tying Prusik loops I have always used the double fisherman’s bend. However, the double fisherman’s is bulky and as a result, never sits quite right on the body of the Prusik Minding Pulley (PMP). I decided to try the overhand rethread as an alternative. There were a few questions I had; would an overhand rethread sit better against the PMP, allow for easier tying of the Prusik hitch onto a rope and still perform well enough when slow pull tested? Check out what I found out with a bonus testing video at the end.
I could go out and buy a sewn loop for the Prusik. However, I prefer to tie my cord so I can custom build my progress capture Prusik to just the right length for the size of the minding pulley I am using. Not too long, so there is only a small delay in Prusik engagement.
As we are trying to use smaller and lighter PMPs, there is less room for the bend to sit properly against the body of the Pulley.
Building and using
The first thing I noticed when tying the overhand rethread (OR) is that it takes a lot less cord than the double fisherman’s (DF). That makes sense if you think about it. The OR is tied with a single overhand, and the DF on a double overhand. My expectation therefore was, the OR breaking strength would be less than the DF. Less rope equals less surface area to absorb the heat produced. The DF used 19cm in 7mm cord per side of the bend and the OR 11cm.
Secondly, it was easier to put the OR on the rope and create a Prusik hitch. The OR was less bulky did not catch as it was being passed through.
Thirdly the OR sat better against PMP, less offset of the pulley and as a bonus allowed for better minding and engagement of the Prusik.
Double Fishermans PMP
Slow Pull Testing
- The cord tested was 7mm Edelrid Power Cord with a 14kN breaking strength.
- Without the bend, breaking strength of a loop would be 14kN x2 = 28kN.
- The ideal result would be more than one-third of the manufacturers breaking strength, i.e., 28kN – 9.3kN = 18.7kN (66%).
Loop tied with double fisherman’s bend
- Test 1: 20.96kN (75%).
- Test 2: 22.62 (81%).
- Average: 21.79 (78%).
- Failure: Both loops broke at the fisherman’s bend.
- Tails: Were pulled into the bend and shortened around 50%.
Loop tied with overhand rethread bend
- Test 3: 17.87kN (64%).
- Test 4: 19.91 (71%).
- Average: 18.89 (67%).
- Failure: Both loops broke at the overhand bend.
- Tails: Did not move.
- The double fisherman did outperform the overhand rethread as expected in the slow pull testing. One result for the overhand rethread (17.87kN) was 0.83kN below ideal minimum breaking strength (18.7kN).
- Considering the use/loading of the Prusik Cord and the failure of the hitch by slipping – the reduction in strength by using the OR may not be significant in the safety factor of the system.
- It was interesting to see the tails on the double fisherman’s bend being shortened significantly during failure. This example is a reminder to tie bends with suitable length tails or pre-tension. The tails on the overhand rethread did not move.
- I have only done a couple of tests in each type of bend so this a small sample size. As always more testing will provide more reliable data.
Check out the video of the testing here.
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