Snatch blocks (1 Viewer)

[e9999]

Been thinking about this for a while and concluding that, although they don't come out and say it, a snatch block's capacity (MRC), which is commonly shown in advertisements and on the packaging, is what it will stand up to for short durations. And that's the duty cycle that most snatch blocks would see. I'm thinking that the WLL is the rating that should be used if were in continous or frequent use. So if I were running a guide business, for example, with a 12K winch on my rig, I'd be looking for a snatch block that has a WLL of at least 24K. If you'll notice, even these H.D. snatch blocks made by Warn, shown on Amazon - 33K & 36K have WLL stamps less than 24K. (24K = 12 tons) And this Warn Epic snatch block is stamped 18 tons - which is 36K, with no WLL stamp.

The way I look at it is different, to me the WLL is the load never to exceed when working, briefly or continuously, if you want to be sure that you are safe. It is unclear to me what some of those manufacturers mean by max capacity, but since the WLL should normally be something like 1/5 or 1/10 of of the ultimate breaking load for safe rigging, and those max capacity seen in ads are often only twice the stated or implied WLL, I gather that they mean something like a proof load where you run the thing and still do not see any visible damage even though you are over the theoretical safe zone. So, I suppose you could take a chance and run it briefly at those "max" loads and get away with it, but that defeats the point of having safety margins. Or maybe you could say that this is precisely the point of having safety margins since the manufacturers probably assume people will take chances or won't know what they are doing.

So, I think that in our context one should look at WLL as the maximum not to exceed to be safe "for sure". Beyond that, you take your chances but you should NOT assume you will be safe. Thinking along the way of "it's only twice the WLL, it should be safe for a quick pull" can be problematic. And remember, as I mentioned above, that the WLL is usually only for ideal conditions (new unstressed device etc) anyway. So the question at the end of the day may be "do you like -or do you have- to live dangerously and if so how much?" To each his own, of course. And sometimes you gotta do what you gotta do.

And that's not even getting into whether you can trust what the company or manufacturer says. Most of this stuff is likely made in China. Do you trust all their "specs"? If some company out there in Shenzen stamps their stuff "WLL 12 tons", do you believe them? Are you sure they have tested this properly? Not directly related, but anecdotally I bought a power bank made in China stamped and advertised "5600 mAh". When I tested it brand new, I got something like 1000 out of it... Let's hope it's not the same with WLL... Yes, apples and oranges, but symptomatic.

All this confusion is likely a result of poor or unclear (or intentionally misleading) use of terminology by companies catering to the amateur market. OTOH, professional rigging devices should have traceable specific and well-defined specs based on published standards, and would be clearly stamped, I would hope, since they will be used for life and death situations. And may also cost 10x as much as what we are talking about here.

 

[Cruzerman]

Living in the Pacific Northwest, we have lots of logging. And so we also have quite a number of rigging shops. I have always gotten most of my recovery gear from these types of shops. Often less expensive than 4x4 marketed gear and purchasing from people who know what they are talking about. And I also recommend a polyester endless (loop) sling. They are so useful in recovery and are the best tree savers.

 

[fjfar80]

I would recommend taking a look at the 7P Overland Recovery Ring, this is the best solution set I have seen. In full disclosure I work with 7P Overland as a trainer / instructor. The designer / inventor of the system is Andy Dacey who is well known in the off-road world. he is a 1990 Camel Trophy competitor and then went on to become one of the event coordinators and scouts. Having worked with Andy I can tell you he is passionate about vehicle recovery and is a damn genius when it comes to synthetic rope, knots, etc. He is the one who taught me how to make my own soft shackles. Anyway, the Recovery Ring is pure genius, simple, strong, and safer to use than a snatch block. Check it out:

The 7P Recovery Ring

- Mark

 

[Randy88FJ62]

$190 for a slightly larger soft shackle and a turned piece of aluminum that has been anodized?

Pros: Very lightweight.

Cons: No wire rope use, must watch the winch line very carefully so it doesn't slip off while tensioning line. Burrs on the ID of the shave could catastrophically cut the dyneema soft shackle whereas a pulley would not. (of course no one would use a damaged shave right?)

FFAR80,
you say small size. What is the overall outside diameter of the sheave and how wide is it?

 

[fjfar80]

Randy -

No, I don't think anyone would use a damaged sheave, just like no one would use a snatch block with a damaged part. Further, most snatch blocks do not have an ideal radius for synthetic winch line use, which leads to compression of the winch line...leading to damage over time. Also, with a regular snatch block you have to inspect the sides, etc. to ensure there are no burs, etc. that could damage the line during winching operations. Less moving parts is always better in my humble opinion.

I've used these Recovery Rings extensively and I have yet to damage them. Could they be damaged, absolutely...just like everything else.

In regard to size it's about 7" diameter, I can measure it exactly with my calipers when I get home.

- Mark

 

[half k cruiser]

@fjfar80 have you measured actual mechanical advantage with say a simple 2:1 ? It would be nice to have some real comparison to a snatch block. Also, I don't remember what my last block was in diameter, but it was fairly decent probably 6"-8" so right in the ballpark as the radius of that ring.

 

[buck208]

Is snatch synonymous with pulley. Have we just used snatch and pulley without giving much thought into the type of recovery operation? I'm fairly new to all of the recovery stuff but was wondering.

 

[Bambusiero]

Little things that annoy me - words have meaning. (without warning, way out of left field, I know...)

Snatch Block - It's a PULLEY, just a pulley - nothing more, nothing less.
No snatching involved.
Not particularly block shaped.
Doesn't become something different just because it's being used for vehicle winching. Not even a tiny little bit different.

 

[Bambusiero]

...Further, most snatch blocks do not have an ideal radius for synthetic winch line use, which leads to compression of the winch line...leading to damage over time...

I've only just become aware of the 7P Recovery Ring, and I must say, I find it to be an elegant innovation, taking best advantage of the unique nature of UHMW polyethylene rope. Plasma / Dyneema, soft shackles, whoopie slings, etc., etc.
Fantastic stuff, but it requires an almost complete re-think of the old ways and equipment.
Like - don't mix & match old steel / cable / chain / "snatch block" usage with new synthetic stuff. Go all synthetic.

But - question about the 7P Recovery Ring design, since you allude to this.
The outer diameter winch line path seems to be way too large in valley radius profile for it's intended function - guiding a 3/8" winch line.
The ideal radius (according to Sampson Rope docs I've read) would be 3/8" + 10%, so the winch line underside keeps a rounder shape, and flattening less. Now, I know that Plasma / Dyneema is pretty OK with squashing flat, so it's not really much of an actual problem, but might just as well optimize, right? So, it looks to as if it was somewhat copied from the arborist rings, which are very similar, but with a different use case (big cushey ropes, static rigging, adapting to odd shapes trees, etc.). The arborists seem to have invented this idea, and have had it around long enough for several for several sources to have copied it. So, the 7P version seems to be a useful re-purposing into a vehicle recovery winch pulley, rather than an original invention.

Care to comment?

 

[Cromagnon]

Little things that annoy me - words have meaning. (without warning, way out of left field, I know...)

Snatch Block - It's a PULLEY, just a pulley - nothing more, nothing less.
No snatching involved.
Not particularly block shaped.
Doesn't become something different just because it's being used for vehicle winching. Not even a tiny little bit different.

Snatching has everything to do with the "name." As defined a snatch block is a block and pulley that allows the reeving of the pulley by opening one of the cheeks to allow a bight of the cable or line to be inserted instead of having to go to the end of the working line or cable. This facilitates operations where there is a permanent fixture on the end of the working line such as a eye or hook as is commonly found on the end of winch cables or lines. In the case of the 7P the block happens to be flexible. The word origin comes from the "snatching" or capturing of the line or cable by the block.

 

[e9999]

I've got several large metal shackles and snatch blocks and I have to say that every time I pick one of them up I am surprised then annoyed at the weight...

 

[phi1osopher]

I was about to buy a snatch ring, and now I am seriously rethinking it.
Thanks for sharing the video!

 

[Bambusiero]

Very interesting video. I applaud the idea of putting this to numbers, and the effort to do it.
However - the heating, or lack of heating...something doesn't seem to add up.

Stating the obvious - what ever in the system that causes inefficiency is absorbing power, by friction, and turning it into heat - so, very roughly, you would expect to be able to detect the level of inefficiency by feel - what gets hot? How hot? It should correlate with the numbers - roughly.

Bow Shackle
The video presenter said the bow shackle, used as a non-moving pulley, got very hot, which does make sense.
After all, that's the very worst sort of pulley that exists, right? (well, after a sharp corner)
But - it was only 3% inefficient, which does not make sense to me.
The bow shackle should be the worst of the lot, by a long way, not even close.

Soft Shackle / Ring
If it really was 69% inefficient, that thing should have gotten really, really hot. Hot enough to damage the soft shackle.
But it didn't, and they don't - so what's going on here?
- 69% of say, 3 to 5 horsepower = 1500 to 2600 Watts - that's a lot of heat.
- The surface between the soft shackle (an insulator) and ring (a conductor) is the sliding surface - where the friction takes place here.
- The soft shackle is made of Dyneema or Spectra UHMWPE . It has a very low coefficient of friction, comparable to PTFE, conducts heat very poorly across the fibers, moderately along the fibers. It's not conducting heat away or absorbing it.
- Aluminum is a much better heat conductor than steel - so what? It's got nowhere to go, but into the metal of the ring.
I don't think the ring has enough mass to absorb that heat without significant temperature rise.
I don't think there's enough surface area or air movement to be an efficient heat exchanger / dissipator.
- The winch line is not carrying away significant heat. Its not the source of the friction, and doesn't conduct or absorb heat well anyway.

So, very skeptical of the particular result presented, and very interested in independent confirmation.
Have been wondering, and would really would like to know the pulley efficiency of the soft shackle / ring system.
It might depend a lot on the exact aluminum machine finish and anodization process.
Maybe room for product differentiation there.

 

[Bambusiero]

Snatching has everything to do with the "name." As defined a snatch block is a block and pulley that allows the reeving of the pulley by opening one of the cheeks to allow a bight of the cable or line to be inserted instead of having to go to the end of the working line or cable. This facilitates operations where there is a permanent fixture on the end of the working line such as a eye or hook as is commonly found on the end of winch cables or lines. In the case of the 7P the block happens to be flexible. The word origin comes from the "snatching" or capturing of the line or cable by the block.

Thanks for the etymology / word origin - I'll buy that.
So - the term "snatch block" has ancient mariner / sailor origins?
I became aware - that profession used a very specialized dialect of the English language.
A few years ago I read "Two Years Before the Mast" by Dana, about his time on a merchant marine ship sailing up and down the coast of California in the 1830s. All in modern American English, but hard to read anyway. About 1/3 regular English meaning, about 1/3 regular English words with specialized sailor meaning, and about 1/3 unfamiliar specialized sailor words. So it seemed.

 

[phi1osopher]

Very interesting video. I applaud the idea of putting this to numbers, and the effort to do it.
However - the heating, or lack of heating...something doesn't seem to add up.

Stating the obvious - what ever in the system that causes inefficiency is absorbing power, by friction, and turning it into heat - so, very roughly, you would expect to be able to detect the level of inefficiency by feel - what gets hot? How hot? It should correlate with the numbers - roughly.

...

I agree 100%, and I am surprised it didn't occur to me as well. I did find it HIGHLY SKEPTICAL that the simple Bow Shackle would be almost the same as the Snatch Block (with a roller bearing), while the aluminum ring would be so much worse. It seems more likely to me that either the videos got mixed up during editing, or the bit of trail was not consistently the same.

I admittedly do not often take my landcruiser places which require winching (much of my off-roading is done in remote parts of Mexico...) , but I truly want to believe that the simple "Snatch Ring" performs as a pulley on par with anything else..

 

[woodsman 44]

Very interesting video. I applaud the idea of putting this to numbers, and the effort to do it.
However - the heating, or lack of heating...something doesn't seem to add up.

Stating the obvious - what ever in the system that causes inefficiency is absorbing power, by friction, and turning it into heat - so, very roughly, you would expect to be able to detect the level of inefficiency by feel - what gets hot? How hot? It should correlate with the numbers - roughly.

Bow Shackle
The video presenter said the bow shackle, used as a non-moving pulley, got very hot, which does make sense.
After all, that's the very worst sort of pulley that exists, right? (well, after a sharp corner)
But - it was only 3% inefficient, which does not make sense to me.
The bow shackle should be the worst of the lot, by a long way, not even close.

Soft Shackle / Ring
If it really was 69% inefficient, that thing should have gotten really, really hot. Hot enough to damage the soft shackle.
But it didn't, and they don't - so what's going on here?
- 69% of say, 3 to 5 horsepower = 1500 to 2600 Watts - that's a lot of heat.
- The surface between the soft shackle (an insulator) and ring (a conductor) is the sliding surface - where the friction takes place here.
- The soft shackle is made of Dyneema or Spectra UHMWPE . It has a very low coefficient of friction, comparable to PTFE, conducts heat very poorly across the fibers, moderately along the fibers. It's not conducting heat away or absorbing it.
- Aluminum is a much better heat conductor than steel - so what? It's got nowhere to go, but into the metal of the ring.
I don't think the ring has enough mass to absorb that heat without significant temperature rise.
I don't think there's enough surface area or air movement to be an efficient heat exchanger / dissipator.
- The winch line is not carrying away significant heat. Its not the source of the friction, and doesn't conduct or absorb heat well anyway.

So, very skeptical of the particular result presented, and very interested in independent confirmation.
Have been wondering, and would really would like to know the pulley efficiency of the soft shackle / ring system.
It might depend a lot on the exact aluminum machine finish and anodization process.
Maybe room for product differentiation there.

the soft shackle ring would be fine for Very limited use because of WLL and cycles of failure

If you winch a lot you would totally get it

 

[Bambusiero]

the soft shackle ring would be fine for Very limited use because of WLL and cycles of failure

If you winch a lot you would totally get it

WLL = Working Load Limit, I assume?
I have noticed that no-one really talks about that with soft shackles the way they always emphasize it with traditional steel bow shackles.
But - maybe that's justified because the failure modes are completely different?
Failure with steel, under load, is likely to be sudden, catastrophic, and dangerous.
Failure in the soft shackle is probably wear & tear, abrasion, fraying. Gradual, one fiber at a time, and visible. And much less kinetic.
There's a bunch of YouTube videos by highline rigging folks where they test various soft shackles and other stuff to failure - slo-mo video & load cell numbers. Interesting.

Cycles of failure - I can see dirt really accelerating the wear-out of these things. They can be washed though.

After that - no experience to have an opinion.
But - Very Limited Use would be my personal goal, for sure.

Have you had a chance to try out (& wear out) the soft shackle / ring system?

 

[phi1osopher]

WLL = Working Load Limit, I assume?
I have noticed that no-one really talks about that with soft shackles the way they always emphasize it with traditional steel bow shackles.
But - maybe that's justified because the failure modes are completely different?
...

Cycles of failure - I can see dirt really accelerating the wear-out of these things. They can be washed though.

After that - no experience to have an opinion.
But - Very Limited Use would be my personal goal, for sure.
...

Cycles of failure - I can see dirt really accelerating the wear-out of these things. They can be washed though.
I can speak to this briefly from my personal experience from another industry: I used to be a rock climbing guide and instructor, and as a climber we treat our ropes as sacred things. One of the strict rules is to try to keep them clean and NEVER NEVER NEVER step on them.
The reasoning is that stepping on the ropes can force dirt, sand, debris to the inside of the rope, where that unseen stuff can work like little baby knifes cutting away and damaging it in ways that sometimes cannot be observed until catastrophic failure...
In a similar way, I would assume that sand, dirt and crap that has worked it's way in our synthetic ropes would likely have a similar effect. Some of this probably is survival mythology, since when climbing the ropes truly are your lifeline... but the whole "keep your ropes clean and NEVER step on them thing" it is strongly supported by the rope making industry and in it's technical documentation.
For me, I choose to respond to the possibility of equipment failure with (1) redundancy, and (2) always treating the scene safety as though I am assuming something will fail in a potentially catastrophic manner. I rarely am in a winching or recovery situation that is actually life threatening; the vast majority of the time if my equipment fails I can simply swap it out, splice a repair, or use some other method to achieve the same basic recovery. In potentially life threatening, property damaging, solo, or extremely isolated situations I fall back on my old climbing training by using a lot of redundancy with my equipment.

Anyway, I expect that dirty synthetic tropes and soft shackles will fail more quickly when dirty than clean, especially after repeated dirty duty cycles. I also expect that "protective sheathing" potentially make it so dirt can be held in there even worse.

my $0.02