Thread: Recovery 101 including acronyms and definitions

Just researching this myself and came across the thread that is reasonably current

I do note that no mention of Australian Standards has occurred. For your info:

Shackles AS2741-2002. The design factor for shackles is 6. Therefore a grade S 16mm shackle with a WLL of 3.2T must have minimum breaking strength of 19.2T. Shackles must also be ductile and deform before failing. The proof test for this particular shackle is 6.4T and it must be proven to pass without deformity and with continued serviceability.

Lifting Chain AS2321-2006. Using 8mm Grade T (80) (800MPa) chain with a WLL of 2 tonne as an example. The WLL is based on a factor of 4. Again there is an elongation minimum requirement before failure. This chain has a breaking load test of 8.2T and a proof test of 4.1T.

To throw a spanner in the works you can compare a similar strength chain that is used under a different standard

Transport Chain AS4344-2001. Using 8mm Grade 70 (700MPa) chain with a lashing capacity (LC) of 3.8T. Note no reference to WWL. The LC and the WLL can not be compared directly as there are different design factors. In this case the minimum breaking strength is 7.5T. The proof test is to a minimum of 50% of this (3.75T). All chain is tested to this proof test and must be free from imperfection etc. Note that the breaking strength is inline with the reduction in tensile strength of the material from 800MPa to 700MPa but there are different testing requirements and load ratings.

The physics are the same. It is just the application of quality control processes and design factors that change in accordance with the use of the equipment.

If you have read this far it's time for the pearler. there is NO recovery standard. There are NO recovery rated points. If there is please tell me the standard that the manufacturer has rated these against. The best guide for recovery has been mentioned and has been developed over numerous years - that is the recovery mechanic's handbook or its fore-bearers.

The handbook mentions that chains and shackles have a safety of factor of 2 in the recovery role. i.e. 8mm grade 70 chain is 3.8T and a 16mm grade S shackle is 9.6T but it is common to just multiply the WLL of shackles x 2. The reasons for the reduced safety factor are the gradual take up of tension and the conservative estimates of the total pull required (TPR) calculations used in the handbook.

TPR is a series of calculations that take into account the ground, slope and vehicle condition. A worst case scenario for my 110.

Bogged in mud over the axles with a 110 at GVM gives a rolling resistance of 1500kg.

A 30 degree gradient gives an additional 1500kg. (mud uphill??)

A busted wheel gives an additional 250kg.

The safety factor is an additional quarter of the running total - 812kg

The Total Pull required is the overall sum which is just under 4100kg.

A 16mm grade S shackle and 8mm grade 80 chain would suffice according to my calculations.

The handbook does not mention kinetic recovery (snatch straps). Speaking to a 20+ year very senior recovery mechanic the forces are simply unknown and there is no design factor or safety factor that can be reasonably applied.

I did pick up a snatch strap however due to their convenience and ability to smooth out shock loads when used with common sense. If I ever need to use a snatch strap in anger (driving away at full blast with plenty of slack) I will revert to a winch and shovel - its safer.

I also opted for some 8mm Grade 70 drag chain given the unlikelihood of the above scenario and the price difference for grade 80 for only 14% increase in outright strength. Interestingly enough a lot of the recovery kits on the market come to a similar conclusion.

Hope that may be of use to someone

Cheers

Glenn

I love going into stores and asking what standard their "rated" gear is tested to.

I like the TPR rating system, it seems to be a reasonable estimation of additional loading by type of additional load.

I've been looking st some Rudd rotating points to replace the fixed eye bolts I have, for size (to fit the holes I currently have) and they out rate what I currently have but are $135- each and are pink.

Conversely the specialist I buy through are of the opinion that given the size of the eye bolt and shackle which allows angular movement without loading of the shackle pin was fine. As pictured, this is the maximum deflection of the shackle when used with the equaliser strap.



Interested in Tanks opinion as to wether or they are too deflected (the pin end of the shackle does not actually make contact with the flange end of the eyebolt). The included angle of the strap is below the maximum allowed to maintain the straps rating.

Assuming the yellow webbing in that last pic is sitting at the load bearing angle then I agree that setup is not doing the recovery point and shackle any favours. Assuming the inside of the recovery point is rounded and not a tube, the shackle pin is too big.

I would not be comfortable using that setup for a recovery as pictured. Even if the numbers printed on each piece of gear are very large, that setup is not loading the hardware in the way it was designed to be used, and certainly not the way in which it was tested.

Why not rotate the recovery point 90 degrees (until the recovery point looks like an O looking from above) so the shackle rotates freely to align to the equaliser strap load?

Then again, even if you rotate the recovery point you will still have the same loading problem if you ever need to set up your recovery pull more than about 10 degrees above or below the line of the car chassis.

Originally Posted by FeatherWeightDriver

Assuming the yellow webbing in that last pic is sitting at the load bearing angle then I agree that setup is not doing the recovery point and shackle any favours. Assuming the inside of the recovery point is rounded and not a tube, the shackle pin is too big.

I would not be comfortable using that setup for a recovery as pictured. Even if the numbers printed on each piece of gear are very large, that setup is not loading the hardware in the way it was designed to be used, and certainly not the way in which it was tested.

Why not rotate the recovery point 90 degrees (until the recovery point looks like an O looking from above) so the shackle rotates freely to align to the equaliser strap load?

Then again, even if you rotate the recovery point you will still have the same loading problem if you ever need to set up your recovery pull more than about 10 degrees above or below the line of the car chassis.

A swivel eyebolt is the ideal and a vertical pin axis is the way to go, in most cases of recovery using strap/cable/rope and shackle with the shackle pin vertical the tower/towee is usually on the same plane as the towed, i.e. the same hill/gradient. a misaligned shackle being used contrary to it's design parameters can easily become the weakest link in the recovery set-up and you don't want to be standing near a flying shackle part, FWD you will find that a shackle in a vertical pin situation (depending on the size of the collared eye bolt hole) will rotate much more than 10 degrees before binding, as stated a swivel eye-bolt is the go, Regards Frank.

The strap isn't indicative of the actual angle when under load. I was trying to hold the strap & shackle at the correct angle (it's pictured at slightly more than when in use) while being rained on. When at the correct angle the shackle isn't making contact with the collar of the eye bolt nor is the outer side of the shackle sitting loaded against the eye.

Frank, in a vertical pin setup why is i that you can achieve more than 10deg rotation before binding but not in a horizontal setup? Or am I reading it wrong?

As I said it depends on the size of the hole, bigger the better, and when you think about it unless you were at the bottom of a vertical climb, why would you need to angle the shackle up, there is always the option of turning the eye to face horizontal if that was the case, but in normal winching up a hill don't see the problem, Regards Frank.

Originally Posted by clubagreenie

Frank, in a vertical pin setup why is i that you can achieve more than 10deg rotation before binding but not in a horizontal setup? Or am I reading it wrong?

Try this next time it is not raining...

Set up your shackle and sling as you did for the picture.

1) Pull the sling tight directly behind the recovery point. Now walk the sling left and right and see how far it goes before it binds. IT will get to the point in your picture and bind.

2) Pull the sling tight directly behind the recovery point. Now lift the end of the sling higher and drop it lower and see how far it goes before it binds. You will be able to get the sling directly above / below the recovery point and the shackle will still not bind.

As a picture is worth 1000 words, for the avoidance of doubt...



So even if the shackle does not bind in the previous picture, loading that way is "not recommended"