Doubled aluminum rings

Serf Life

Well-Known Member
Thinking to splice two dmm rings together with 12 strand to make a dead eye or small ultra sling to use in lieu of x-ring. 1/2" rigging rope only. Good bend radius and strength, but curious if there would be downsides? I have a number of extra rings just sitting around and trying to think of ways to use them.
 

JeffGu

Well-Known Member
I'm not entirely sure why people think two rings doubles the bend radius... it does no such thing. If the stock the ring is made of is 1/2" diameter, the bend radius is 1/4". Stacking two such rings alongside of each other gives you two 1/4" radius bends with an effectively flat space between them. Although this provides more friction (with more than two), it doesn't change the bend radius. Increasing the diameter of the stock material used to 1" will double the bend radius.

The bend radius affects the percentage of rope fibers that are under tension and compression, limiting how many of the fibers are allowed to elongate under load... hence the importance to load capacity of the rope passing through the device.

If you're after more friction, stacking the rings will provide that (more than two). If you're after increased rope life, increase the stock material diameter of the rings, or switch to pulleys.
 
Last edited:

Serf Life

Well-Known Member
Good explanation thx. My incorrect understanding is from the increase in distance between the two radii. Instead of the outer rope fibers stretching in a half inch semi circle they are making it in one inch, albeit not a larger diameter circle. Hope that makes sense, I see my error and others may have got there for a diff reason.
This project would be to not have gear laying around unused and more practice splicing, less rope wear is nice but my main thought behind using two was added strength/safety.
 

JeffGu

Well-Known Member
Yeah... you would gain strength of the hardware, which might be nice if your cordage is lots stronger than a single ring's rating.
 

SeanRuel

Well-Known Member
@JeffGu Can you point me to any sources that explain strength/ bend radius. To me it instinctively seems like there is some benefit from the separation of 90° bends. Love learning things that contradict my assumptions.
 

JeffGu

Well-Known Member
I would expect there to be a difference... you'd have to perform break tests on a lot of ropes/rings to see how much difference... but I certainly wouldn't expect it to be as much as increasing the actual bend radius would provide. Rope OEMs recommend an 8:1 ratio sheave/bollard diameter to rope diameter, but usually say 4:1 is acceptable (because it's a lot easier to achieve, realistically).

You'll have to hit the Googlizer for mo' info, Sean. I've been operating off of a netbook since I tore down the desktop 'puters to move them to this house, but haven't actually done it, yet.
 

Brocky

Well-Known Member
I would expect there to be a difference... you'd have to perform break tests on a lot of ropes/rings to see how much difference... but I certainly wouldn't expect it to be as much as increasing the actual bend radius would provide. Rope OEMs recommend an 8:1 ratio sheave/bollard diameter to rope diameter, but usually say 4:1 is acceptable (because it's a lot easier to achieve, realistically).

You'll have to hit the Googlizer for mo' info, Sean. I've been operating off of a netbook since I tore down the desktop 'puters to move them to this house, but haven't actually done it, yet.
So the largest diameter that should be run through a 12mm diameter ring would be 3mm going by the 4:1 recommendation?
 

JeffGu

Well-Known Member
I believe the suggestions are for moving rope, but yes. I don't know what the recommendations are for a static configuration. I suspect that rope strength degradation from knots, splices and friction elsewhere in the system are greater than that induced by the termination hardware, so it becomes fairly insignificant if the rope isn't loaded above SWL with a high enough safety factor.
 
Last edited:

Brocky

Well-Known Member
I wonder if the rope were stationary and the bollard, or something similar were moving, would the same ratio be recommended?
 

JeffGu

Well-Known Member
I don't know... that's an interesting question, though... obviously, the rope would still have to be loaded. I think friction heat from the spinning bollard would be the big problem. Sheath would glaze and would give first.

I think bend radius issues are mostly about the long term weakening of the rope from most of the load being carried by a smaller percentage of the strands. This gets spread over the entire rope as it moves over the bollard/sheave/ring/whatever when the rope is moving. I think turning the bollard is a whole different animal.

I tried to break three pieces of Cherry Bomb to see if I could see any difference between a 3/8" SS shackle in a spliced tight eye, and the same shackle with the pin diameter increased with a couple of different methods (3/8" I.D. air hose, and 3/8" I.D. PEK tubing) but all of them broke at the splice, not the shackle. However, it was easy to see that the part of the rope forming the eye looked much worse on the pin by itself. The eyes of the other two showed no crushing and less elongation of the eye after being pulled to rope failure. So, I still do this... increase the bend radius of the shackle pin. It has a quite noticeable effect on the rigging lines with a shackle through a tight eye, because they get a more brutal workout. Some of those, the eye was actually big enough for me to increase the diameter of the pin to 3/4" and when I've taken the shackle off, the eye looks just like it did when I installed it. The ropes with just a steel carabiner through the eye look much worse.

This isn't a high failure point, though. But, for the long term life of the rope, it is the worth the little bit of effort, to me. It seems like the increased bend radius is important for a mostly static end termination, but not as much as moving rope on a ring/bollard/pulley/etc.

So, no... I think the recommended ratios would be different for such applications than say a friction bollard or a block in rigging.
 

Chaplain242

Well-Known Member
I would suspect that the rigging choke angles chart would apply and that with one ring 100% of the load is distorting the rope/bend and by the rigging choke angles chart the load factor is 0.49 (0deg to 30deg). The two rings would have two 90deg bends which by by the choke angle reduction chart would have a load factor of 0.87....
 

Brocky

Well-Known Member
I didn’t think to mention that the bollard didn’t rotate. My questions were a sneaky way of pointing out the illogical use of rings on rope bridges, most seem to be only about a 1:1 ratio.
 

JeffGu

Well-Known Member
I think this could be tested with break testing... if you reduced the diameters to a point where the damage would be severe enough to ensure the rope breaks at the ring(s). Using 1/4" diameter rings with 1/2" rope, for example. Then just start stacking the rings and see what happens. Does the rope break at higher, or lower, forces as you add rings?

I honestly don't know if the separation between the rings has any effect, but I'm still fairly certain that increasing the ring's stock diameter to 2x will have a more beneficial effect than using two (or more) rings of 1x stock diameter.
 

JeffGu

Well-Known Member
...rings on rope bridges...
Yeah, it's a kinda creepy thing... makes a good case for using overkill on the materials and replacing the bridge often. I'm pretty sure a carabiner or a ring wears that little piece of rope out faster than most of the things we do to ropes.
 
Yeah, it's a kinda creepy thing... makes a good case for using overkill on the materials and replacing the bridge often. I'm pretty sure a carabiner or a ring wears that little piece of rope out faster than most of the things we do to ropes.
What should I be using instead of a ring?
 

LordFarkwad

Well-Known Member
Hopefully someday there will be something with more advanced materials.
View attachment 65569
Something like the Hydra but replacing the pulley with a wide low friction ring. It could maybe also have stainless steel inserts of different inner diameters.
Since you mention this, what is the word on the CMI CA swivel? I'm running one of these on my bridge for the past half year or so, and I like it, but boy does that thing have some edges.

What will signal the need to retire the bridge? I'm running the stock TM bridge (Globe 3000 or whatever), with a secondary bridge (Teufelberger 10.5mm Platinum) knotted to the lower D's in parallel with the factory. I use them both together as a single bridge, always.
 
Top