Recovery Ring Double Rigging

[Metcalf]

Here is a good visual for how the strength of Dyneema fibers react at elevated temps.

Remember, every fiber in that rope has to be at those temps to see even this small decrease in ultimate performance. We should not be operating the rope anywhere near MBS even in drag recovery. The rope winch rope should be sized at a minimum 2:1 FoS for the max pull ( 1st layer ) performance of the winch.

Side note: it actually gets STRONGER than advertised at very low temperatures.

 

[DaveInDenver]

Interesting point about insulating. Would point out that it's the first layer on the drum that's the one that is exposed to the most heat from the motor and brake. So the operator should be thinking of heat everywhere in the system.

https://pelicanrope.com/content/PDFs/Dyneema-Comprehensive-factsheet-UHMWPE.pdf

For comparison (all in W/m*K)

Air = 0.25
Water = 0.598
Glass = 1.05
Mild steel = 50
Aluminum = 237

 

[Metcalf]

Interesting point about insulating. Would point out that it's the first layer on the drum that's the one that is exposed to the most heat from the motor and brake. So the operator should be thinking of heat everywhere in the system.

https://pelicanrope.com/content/PDFs/Dyneema-Comprehensive-factsheet-UHMWPE.pdf

View attachment 783373

View attachment 783374

For comparison (all in W/m*K)

Air = 0.25
Water = 0.598
Glass = 1.05
Mild steel = 50
Aluminum = 237

Yes, and that is why I prefer to run winches that have the brake and motor system out of the drum.

The only true thermal rope damage I have ever seen is from a poorly setup in-drum brake system that was often time powered out instead of free spooled because the lever was stuck. That did create very high temps that damaged the synthetic winch line. With what I saw for fiber damage, I would say it was well over 400F at times.

 

[Metcalf]

Here is an excellent explanation about some of the thermal properties of the Dyneema fiber by the company that invented it . Well worth the watch.

 

[ScottPC]

I realize there has been a lot stress testing on the synthetic ropes and soft shackles but I have not seen destructive test results on the actual rings . With a bow shackle, the bow will begin to deform under excessive loads before failing. Theoretically in a 4:1 systems with a 10K winch you could see forces of ~40,000 lbf and with a 16.5 ton winch, near 70,000 lbf before the winch stalls. Granted these forces are very rare and other things in the system may fail first but what are the ring's failure characteristics. Do they split, separate, fragment? Is it a gradual degradation or an immediate catastrophic failure?

 

[Metcalf]

I realize there has been a lot stress testing on the synthetic ropes and soft shackles but I have not seen destructive test results on the actual rings . With a bow shackle, the bow will begin to deform under excessive loads before failing. Theoretically in a 4:1 systems with a 10K winch you could see forces of ~40,000 lbf and with a 16.5 ton winch, near 70,000 lbf before the winch stalls. Granted these forces are very rare and other things in the system may fail first but what are the ring's failure characteristics. Do they split, separate, fragment? Is it a gradual degradation or an immediate catastrophic failure?

The first thing you will see is some permanent deformation (elongation) of the ring. That is easy to check for with a set of calipers. The 6061-T6 material I use in my rings will show visible (plastic) deformation well before an ultimate failure above 100klbs.

It's easy to add the numbers up and get a bit concerned, but I have yet to see ANY ring failures across the industry. There is always a limit, but the practicality of being able to anchor these forces is a bigger concern to me. There are very few natural anchors or connections to a vehicle that would approach the ultimate failure of the ring.

On the technical side of things, Only with double rigging, 1 or 2 legs are going to be trying to stretch the ring from the inside. The other two legs around the outside have far less mechanical advantage on the ring.

It would be impossible to ultimately fail my recovery ring with 3/8 or even 7/16" good quality winch line. You just can't generate enough force before the winch line would fail ( and we shouldn't be rigging anywhere near to ultimate failure on the winch line in good practice). You should absolutely be thinking about the doubling up the soft shackle if you are rigging a 3+:1 mechanical advantage system however, and spreading that load out to multiple anchors and recovery points.

I wouldn't recommend double rigging my ring with a 16.5 TON winch , but I think that was a typo.

 

[ScottPC]

One scenario where this simple 4:1 MA system would think would be is when very close to the anchor point and you may still have a few wraps on your winch which reduces it's pulling force. It may also not be practical to spool out all of the winch line to get to the final wrap for the max pulling force while also using and X block to shorten the line for a 2:1. This might be a re-riggiing final pull scenario where the stuck forces are known.

On a different note, I would love to see a 2:1 MA comparison where rings are spinning around the soft shackle vs where the rings are stationary and the winch line slides around the ring and/or through the ring. In one case you'd have the concentration of friction on the soft shackle and in the other case it would be mostly on the winch line. Does this do significantly more damage to the winch line? Which technique is more likely to experience failure?

 

[Metcalf]

One scenario where this simple 4:1 MA system would think would be is when very close to the anchor point and you may still have a few wraps on your winch which reduces it's pulling force. It may also not be practical to spool out all of the winch line to get to the final wrap for the max pulling force while also using and X block to shorten the line for a 2:1. This might be a re-riggiing final pull scenario where the stuck forces are known.

On a different note, I would love to see a 2:1 MA comparison where rings are spinning around the soft shackle vs where the rings are stationary and the winch line slides around the ring and/or through the ring. In one case you'd have the concentration of friction on the soft shackle and in the other case it would be mostly on the winch line. Does this do significantly more damage to the winch line? Which technique is more likely to experience failure?

Generally, UHMWPE is a wonderfully low friction material, especially on a polished aluminum surface. I've been using these systems for many years now and have had very minimal wear on the winch line or the soft shackles. I find the wear to be similar to any other use case, but I have winch lines that have made it to the 10 year mark and now I just feel guilty about retaining them, but they are still very functional.

I don't believe there is any 'damage' done to the winch line using these systems within realistic operating conditions. I am still FAR more worried about the heat generated in most recreational market winch brakes than I am about the 'friction' in these systems.

I don't see much practical difference going around the ring or through the ring. Around the ring will typically be a slightly larger radius so I prefer using that when I can. Which part spins and which part stays stationary is a bit of a force balance equation....and doesn't always work exactly like you expect them to. For example, at lower angles ( say less than 90 degrees ) going 'around' the ring, the ring won't necessarily spin.

What these modern recovery ring systems do is provide a TON of flexibility in rigging at a very low weight and cost with very few moving parts to maintain. It gives the user more options. Being able to rig a 3-4-5:1 mechanical advantage with basically no additional components is a huge savings in complexity and stored energy in these systems.