I’ve got some new info on the big rings available for the U-SAVER ……..
The U-S is an AFS with two special elements: the retrieval tail (Wichard shackle) and the extra large ring (2.5” ID).
The shackle allows remote installation directly from the climbing line, soft and double-ended retrievals, and eliminates the need for a separate retrieval ball. Since it isn’t load-bearing, it’s a no brainer addition.
The big ring is more problematic. Currently, no industry vendor offers a marked ring big enough to pass the pinto and the arborist rings. But it’s that big ring that allows the best of best worlds: reliable choking configurations on the stem plus hanging configurations that install remotely, like any R/r FS.
With no marked ring available, I’ve sourced two rings from vendors of quality marine rigging hardware. They are shown on these links:
West Marine WM 534206 retail $13.49
link to West Marine
Titan Marine TR223 retail $57.93
link to Titan Marine
(Thanks again, AJ, for the tip on Titan).
(I’ve disqualified the custom ring from Allied Titanium, posted earlier, due to cost. The engineering drawings are
HERE. In full production quantities, I would expect the cost to be comparable with the Titan ring. In unit quantities, the cost too high, approx. $100 ea.)
This post compares these rings and discusses testing I’ve done to convince myself that the rings are an appropriate choice for my climbing.
Happily, I can say that both rings have earned the coveted IMOA Certification.
(Like so many ideas in this wonderful forum, each individual will need to make a choice for himself. IMOA stands for “It’s My Own As*).
SURFACE
The WM ring is a polished mirror finish; the T ring is a smooth, matte finish with the look of (sorry) titanium. The Titan finish seems smoother than a sand-blasted finish, hence the term matte. Both are very friendly to running rope and I can discern no difference in the sliding friction.
Both rings exhibit a great feeling of quality, very much better than rings that are welded and then ground/polished. The titanium ring has a more “precise” surface than the steel ring. This is discernable only with a micrometer, not by eye or by touch. The WM ring is forged and you can measure “waves” or “ripples” in the section diameter. The T ring is investment cast and the section diameter is more consistent. This property has no impact on daily use, but the WM section irregularities contributed to experimental error in the Strain/Strain tests, discussed later.
SIZE and WEIGHT
Both rings are nominally 2.5” ID. Nominal section diameter: WM ring 7/16”, T ring 25/64”.
Weights as follows, compared with common items:
Small Al arbor ring 1.3 oz
T Ring 2.6 oz
Large SS arbor ring 5.6 oz
WM ring 7.4 oz
When you first pick up the T ring, there’s a definite “wow” factor.
BEND RADIUS
The T ring looks distinctly “skinny-er” than the WM ring. It is actually 3/32” thinner. This has implications for bend radius as follows:
In choking configurations, only the Tech Cord, not the climbing line, passes over the large ring. In these configurations, there is no issue.
In hanging configurations, the large ring carries the climbing line along with either two (2) arborist rings or with the pinto. The following photo shows the bend radius with Arbormaster and it seems just fine.
I would not, however, suggest the T ring for a “normal” AFS where the climbing line passes through the T ring and only one (1) small ring. Bend radius seems too tight.
Here are the rings bend diameters compared to some common items so you can make you own judgment:
T ring .371" 9.4mm
DMM Oval Crab .395" 10.0mm
DMM Revolver sheave .432" 11.0mm
Petzl William Crab .457" 11.6mm
WM ring .462" 11.7mm
DMM arborist ring .473" 12.0mm
ISC large arborist ring .479" 12.2mm
STRENGTH
The ring vendors publish these specs for the big rings:
WM steel: 1350 LBS Max Working Load
Titan titanium: 3528 LBS Rec. Safe Working Load, 7056 LBS Max Safe Load
Special Note: I have made written inquiry of these vendors to define the precise meanings of their strength specs. About a month ago, I was told by West Marine that there was an “error” on their web site. Just days ago, the site was changed. The number shown now is the “working load” listed above. Previously,, this ring was listed as “25,028 LBS MBS.” Now they show the “working load” not the “breaking load” for this family of products. I don’t know if the 25K was truly in error or they made a policy decision to show only working load. It is, however, consistent with what I would expect from a steel ring of this dimension. Similarly, I don’t know the safety factors that these engineers are applying to these figures.
I don’t have facility to test at the 25000 LBS level. I did set up a strain proofing test for both rings at ten (10) times my working load or 2000 LBS. Both rings came through the test with flying colors, indicating that they were “loafing” to handle that level of stress. The specifics of this strength testing are shown below. Fair warning: if you thought this post was boring so far, this will make your eyes bleed. Geeky! I’m posting it only in the hope that someone might want to run these tests into higher stress levels.
Proof Testing Rig (video)
here
Data and Calculations
here
Comparative section strengths
here
Anyway, that’s it. Here’s my bottom line ----------
I’m OK with both these rings for me, personally. However, I’m going to keep the WM ring on my primary U-SAVER, just because I’m completely happy with how that rig is working for me. With the 10mm/33kN OP, the 50 kN pinto and the steel big ring, I get the feeling I could pull a Volkswagen into the tree. As a primary TIP, it feels bomb proof.
However, for a secondary crotch or a re-direct, the original U-S seems too much. So I’m going to use the titanium ring to build a “sports car” version, something that feels more like a Revolver on a runner: smaller, lighter. But I still want to set it remotely and retrieve it remotely. You’ve heard of “Mini-Me”? This will be the “Mini-U”, with titanium. I’ll post pix when I get it built.
OF
Ps.
This work is the best I can do with limited tools. It’s no substitute for an industry vendor getting interested and doing this right … !
