D Shackle & Recovery Questions

typical 3/4" shakles are rated for around 20,000lbs static.. so get gear that will at least meet the weight of your rig, and all of your gear.. if your truck weighs 5000lbs.. get gear rated at 10,000lbs or more.. this gives you a safety margin, and provided your gear is well taken care of you shouldnt be breaking any of it.. if a tow strap or rope shoes wear, fraying, or otherwise add it to your list of items that either need repair, or replacement the next time you hop online for your next trip. always check your gear every month or so..

 

Check out the stuff from Gear America.

$43 GearAmerica Mega D Ring Shackles – 68000 lbs Capacity, Stronger Than 3/4" D Rings –Tow Shackle, 7/8" Pin & Washers – Securely Connect Tow Strap or Winch Rope for Off-Road Recovery – Black, 2-Pack

https://www.amazon.com/GearAmerica-...d=1572278391&sprefix=gear+amer,hpc,215&sr=8-9

 

How is tensile strength calculated? And how does it compare or factor into MBS and WWL?

 

After using a soft shackle for the last 2 years, I wouldn’t use anything else. They are safer, stronger, lighter, and simple to use. And you can wrap them around anything. You don’t get overland points for hanging them off your rig like a normal shackles, but it’s well worth the switch.

https://www.bubbarope.com/gator-jaws-synthetic-shackles/nexgen-pro-gator-jaw-synthetic-shackle-5-16

 

Tensile strength is a property of a material. It's tested using a specially prepared sample of a specific area, and pulled to destruction. The amount of force required and the area of the sample can then be used to calculate the tensile strength (in the US expressed in lb/in^2). Wikipedia has some decent info https://en.wikipedia.org/wiki/Tensile_testing.
This type of testing also determines Young's modulus (also elastic modulus or modulus of elasticity) (in the US expressed in psi), which is the relationship between stress(load in psi) and strain(deflection in inch/inch) in materials. This tells you how 'stiff' or 'elastic' materials are. For a given load, a high Young's modulus material (synthetic rope) doesn't stretch very much at all. A medium one (steel) will stretch a bit, and a very low one (rubber band) will stretch a lot.
Tensile strength is also more accurately referred to as ultimate tensile strength. This is the failure point of the material. This is to distinguish it from the yield strength of a material, which is the point at where it starts to plastically (permanently) deform. Below the yield strength, materials are elastic (like really stiff springs) and will regain their shape once a load is removed). Above the yield strength (but below the ultimate tensile strength) materials will not return to their original shape after the load is removed; they're permanently deformed. A common example for most gearheads is a torque to yield head bolt. Above the ultimate tensile strength the material will continue to elastically deform until it fails

MBS is minimum breaking strength. It's the minimum value that something (shackle, strap, etc..) should break at when in good condition and used properly. This is a very common type of rating on off road recovery gear.

WLL is working load limit. This is the allowable loading for something after the required design margins are applied (for example most overhead lifting rated gear is required to have a 5x design margin). This is how rigging and things used for overhead lifting are rated. It's only common in the off road world when looking at shackles. For most overhead lifting gear you'll encounter in the offroad world, you can convert WLL into MBS by multiplying by 5.

The tensile strength plays into both MBS and WLL in the design of a piece of equipment. The designer will select a material (which has a specific tensile strength), then size it based on the tensile strength to meet the required overall strength. They'll then likely perform destructive testing to verify they got it right.

 

Just an FYI, that soft shackle you linked to is rated for a breaking strength of 26,000 lbs. Common 3/4" shackles have a WLL of 4.75 ton, or 10,450 lbs. However, since shackles are overhead lifting gear, they're designed with a 5x (or more) margin. This means your 4.75 ton shackle has a breaking strength north of 52,000 lbs. The off road world is rife with products advertising their strength as breaking strength when most other industries that use rigging use the working load limit, which has a margin built in.

 

Soft shackles are absolutely not stronger than steel. I dont suggest wrappung them around sharp corners either.

 

That’s entirely dependent on which one you buy. Regardless, the benefits of using soft shackles absolutely outweigh the use of steel shackles. And I imagine everyone in here would realize you’d never wrap it around a sharp corner. Just like you don’t attach a tow strap to hitch ball. Cheers.

 

You are pretty much wrong on all accounts.

https://usarope.net/why-choose-dyneema-rope-vs-steel-wire-rope-for-heavy-duty-rigging/
https://blog.ronstanindustrial.com/is-synthetic-rope-really-15-times-stronger-than-steel-cable

Synth lines are FAR stronger (up to 15x) for the same weight, or you can have a similar strength, but far lighter component.

They have their disadvantages, but strength is NOT it.

Just like with the tow strap/snatch strap debate, there is a reason to carry both. If all you carry is soft shackles and all you can attach to is a sharp corner, you're kind of useless, aren't you...

But I do like to point out in these types of debates that steel isn't any less "safe" than synth, *when used properly*. Sure, if you like standing right next to your winch line while it's under tension, or put your face near a loaded shackle, yeah, synth is safer. But that's stupid. Don't do that even with synth line/soft shackles!

If I were a betting man, I could easily imagine that injuries have actually gone UP since the advent of synthetic winch rope, because instagram squids in their "overlander" rigs make stupid choices when recovering a vehicle because their synth line is "so much safer". The old timers and cheap bastards (i.e. me, lol) who run steel cables understand you should stay clear.

 

Neither of your links are relevant as they are comparing synthetic to braided steel wire rope, not steel shackles. I never addressed wire rope.
Then you state that synth is stronger, qualifying that with "for the same weight". Again, an issue I never addressed.
So no, I'm not "pretty much wrong on all accounts".

Is that your thing, you come in and spout some things that may be accurate, but have no bearing on the discussion, attempting to refute points that were never made?

 

Obviously the links I provided weren't directly about shackles, but thanks for pointing that out, I got confused there for a second.

However they do go in to pretty good detail about the general differences between the two materials. The point of my post was to demonstrate that as a material, synth is stronger than steel by weight which directly refute your blanket statement about synth (shackles) being "absolutely not stronger" than steel. Comparing by weight or at least diameter is really the only way you can legitimately compare the strength of two materials. A 4" thick rubber band will hold more weight than a 1/8" steel cable, but rubber is hardly "stronger".


But here, since you asked nicely, here are some SHACKLES:

Bubbarope Mega Gator Jaw 76,000# breaking strength
https://www.bubbarope.com/gator-jaws-synthetic-shackles

There's even one with a 125,000 breaking strength.

It took a bit to find a shackle that shows the breaking strength, since most only show the rating (4.75 ton usually)

Ryno 3/4" steel shackles 20+ ton (46,000#) break strength.
https://www.rhinousainc.com/products/d-ring-shackles

Hell, even the $44 Bubbarope NexGen Pro (3/8") has a higher break strength than the steel at 47,000#.
https://www.bubbarope.com/gator-jaws-synthetic-shackles/nexgen-pro-gator-jaw-synthetic-shackle

 

I stayed at a Holiday Inn once.

 

What seems to be missing in all these discussions is some theoretical or empirical number on how much strength you need. Most of us are not hanging our trucks overhead, which is where the rigging ratings come in. Pulling a 5000# truck against a coefficient of friction of 1.0 between tires and ground theoretically is a 5000# load on the tow strap or shackle (oversimplifying hugely about things like weight distribution, static vs sliding friction etc). Add in the effect of “locking in” the towed vehicle with obstacles under the frame or in front of the tires, and you could need far more than strength than that (plus factor of safety). But the pulling force may be limited by the traction of the recovery vehicle, though that may be strapped in, or you may be using a winch. Given that it’s not uncommon to have 8-12K pound winches, should straps and shackles be rated to 8-12k working load?

I have no practical experience here, though I will say that the one time I blindly connected a tow strap to an air conditioning line, that had a loop right next to the tow hook (on a car, not my Taco, learned never to hook up a tow strap just by feel) it was strong enough for a 4Runner to easily yank the car out of a snow bank and tow it 1/2 mile up the rest of the hill ... before it broke.

 

There are actual formulas done by the smart people. recovery gear is rated higher than the vehicle weight because while that 5,000 lb truck is easy to move on flat sooth ground, how about if mired in mud to the axles? to the frame?

an old Army manual FM 20-22 is still a great reference to answer these questions.

oh, to the frame in mud, your 5k truck now "weighs" 10k

 

Thanks for the link to the 1962 Army field manual. That will be fascinating reading!

 

It's not missing, it's here:

https://www.tacomaworld.com/threads/recovery-formula.44153/

It's a lot to read, along with all the other various posts and writings on the subject.

Suffice to say the *minimum* winch rating you should have is 1.5x your vehicle's GVWR. Not how much it weighs now, but the MAX if should ever weigh. *minimum*.

Any time I hear about minimums I think of this guy:


As far as the weakest link, IMO the weakest link should be the thing that is least likely to kill you if/when it fails. To me, that's the winch. If your winch fails or gives up, you simply stop pulling, and you wait for your winch to cool down.

But if you've got a 10k winch and a shackle that'll fail at 9k, your winch will keep right on pulling until the shackle fails. Now you have a heavy projectile. That's no bueno.

 

Not sure if this has been covered but in some of the posts I notice some people use (T) and (t). If we are discussing load limits we should all understand there is a difference between the two T/t's. Upper case is for imperial/US Ton = 2000lbs and lower case is metric ton = 2200lbs. May not seem like much but when discussing 4-5 ton WLL and design factors of 5x it adds up. Another detail difference that is found on Crosby gear is load angle and the lettering is also an indicator of wear. When the letters are worn away the shackle is to be disposed of per Crosby. I will again advise every body to read all that they can from https://www.thecrosbygroup.com better to know then assume.

 

Actually, perhaps what I meant was “how much force is needed”. The Army field manual does address this, sort of, and pretty much says that for a vehicle stuck in mud, the extraction force could be many times the weight of the vehicle. So 1.5x is just a target, but not really based on recovery physics. However ... you stated that your winch should be the weak point and made it clear that if it shuts down due to overheating (and drawing too much current, I assume) before anything else breaks, that’s the safest weak link and effectively a fuse. I never thought of it that way - thanks. Though if one uses tackle to increase the pull ratio, one should probably have shackles etc which are 3x the winch rating, no?

 

That's certainly part of the equation, but motor HP is a big part of that, too.

But I guess that's more about how easily it pulls that weight.