Recovery System Design HELP and the Weak Link

[Islandnomad]

Since joining AULRO I have read with great interest this recovery section. It has made me rethink my system, which I use mainly for beach recoveries. It seems to me that for a Snatch Recovery all items used and their SWL's should be considered.




If you assume that the system consists of:
1. Recovery points on bogged vehicle, lets assume a front recovery so 2 recovery points
2. 2 x shackles
2. An Equaliser strap
3. A Snatch Strap
4. Another single shackle
5. A Tow bar recovery hitch


Shouldn't the design of this system be designed to break, so that debris doesn't fly everywhere and kill someone? I would have thought that if the equaliser was designed to break first that the safest outcome would be achieved ie. steel shrapnel would not be flying all over the place.


I have a D2 and am wondering when I buy this system what ratings I need to be specifying prior to purchase?


I think I'm on the right track with this, any help would be appreciated.


I am thinking of buying Philco's (a member on here) recovery points or similar.

[BadCo.]

Rating consistency might be an issue.

I'm not super experienced at recoveries but in my head I would use as big as you can fit (or 1.5x GVM) and if you are worried you can get those straps for the shackles to stop them flying.

Also people tend not use shackles between the equaliser and snatch, just thread the bridle through the snatch. They won't bind together because the eye is strengthened/hardened/extra stitching/what ever, from what I have experienced.

I also use a bridle/equaliser front and back if possible.

Bad

[Tank]

Don't use recovery points that orientate the shackle pins in the horizontal plane as the shackles will become the weakest point if they are not pulled on from directly ahead, shackles aren't designed to be pulled off centre.
A good recovery point will have the shackle pin hole orientated vertically, allowing the shackle to align itself with the direction of pull. if you use a bridle strap, use the longest you can buy, the angle created in the legs of the bridle strap should be kept as low as possible, a 90 degree angle will double the load on the bridle strap. With the legs of the strap together the SWL doubles the further apart the SWL decreases.
If you must snatch prepare the groundwork around the bogged wheels.
The IDEAL snatch/recovery should be mounted in a boxed and reinforced end of chassis rail with a swivel collared eye bolt going through (but not attached to) the bull bar, you can buy "RATED" shackles and eyebolts through Rigging Supply outlets, usually cheaper than 4WD stores, try Bullivants for a start.

[Islandnomad]

Tank,
With the "recovery points that orientate the shackle pins in the horizontal plane" issue if you reverse the shackle and have the bow end at the recovery point, and the pin in the equaliser loop, doesn't the "pulling off centre" issue go away? If that's the case then the 12mm plate or 20mm plate recovery points that people are selling would be ok wouldn't they?


Otherwise a swivel rigging point would be the other option or maybe a JATE ring. I think the military have been using JATE rings for a long time. See photo of a D2 with these fitted.
https://www.aulro.com/afvb/images/imported/2014/08/476.jpg


Haven't heard anyone talk about the weak link idea of mine, maybe I'm getting off the track with that.


Most standard Snatch straps are 8000kg SWL I think, not sure what rating shackles are correct to use?

[Blknight.aus]

Bow shackles can be pulled on almost any which way so get them.

The weak link in the recovery system should ALWAYS be the pulling source. (the winch, the drawbar pull or deadweight) of the vehicle or the rated effort of your recovery device. This means that every part of your system should be below its maximum limit when the winch stalls from overloading.

So if you have a winch with a bottom line pull of 4000kg the shackle and chain that you use to anchor the end of the winch rope should be rated to 4500kg (4001kg would work but they don't make a shackle that size) your snatch block should be rated to a minimum of 8000kg and the equipment that you use to attach the block to anything else should also be rated to at least 8000kg.

Bridle straps and shackles are another story, on paper each end should be rated to about 2/3 of the pull that's going to be placed on the center but for various reasons I personally recommend that each end should be able to handle the full pull of what Ever is going to be applied.

Snatch straps should be rated to a minimum of 2* the gvm of the vehicle doing the pulling and ideally less than 5* the weight of the vehicle being recovered (insert caveats for all other safety requirments and inspection regimes for snatch type recovery gear here.)

[Islandnomad]

Dave
If the weak link in the recovery system should ALWAYS be the pulling source, then shouldn't it read "This means that every part of your system should be above its maximum limit when the winch stalls from overloading"?

I don't have a winch so following this logic it means that the Tow bar recovery hitch which is rated at 4.75 ton (its hard to find a rating on any of them see an example below) should be the weakest link in the chain, or alternatively it's single shackle.


The reason I suggested that the equaliser should break, is that I thought that it would be a safer event than a shackle breaking and flying back at the recovered vehicle???? Why does the pulling source always have to be the weak link?
https://www.aulro.com/afvb/images/imported/2014/08/473.jpg

[FeatherWeightDriver]

^^^ What they said ;)

Winch recoveries the winch will stall once you get to a certain load, so all of the other links in the chain should be at least as strong as that stall force. Note if you use a pulley that effectively doubles all of the ratings you need.

Tank's "vertical shackle attachment" is to minimise the shackle twisting across the plane of the pin - as this only decreases the breaking strengths of the shackle and attachment point. What you are trying to avoid is the scenario shown here: http://www.aulro.com/afvb/recovery/174282-recovery-101-including-acronyms-definitions.html#post1935404

As for snatch recoveries, use the strongest gear you can afford, start out slow and gradually increase the snatch forces involved.

By the time any piece of gear break in a snatch recovery the forces involved are almost certainly measured in tonnes, and there is no hope in hell of controlling the mode of failure. Even a snatch strap breaking and hitting the back of your truck (without a shackle) will break glass and/or punch a sizeable dent in the panel work.

See 10 minutes and 10 seconds in to this clip:

https://www.youtube.com/watch?v=ZSlOH7LHVxk&feature=player_detailpage#t=501

I have seen snatch straps which have secondary attachment points in case the main eye fails, but I would guess there would be 10s or 100s of mid line failures for every eye failure. They also claim to help with shackle and attachment point failure, but if you just broke a rated shackle and your strongest attachment point, your backup is probably just going to get torn apart as well.

[Islandnomad]

I do understand Tank's vertical shackle attachment attachment issue (see photo below), I question whether in that photo whether the shackle is placed correctly though, as I have said twice, if you inverted or reversed the shackle and had the shackle pin at the web loop and the bow at the recovery point, doesn't his issue go away??????
https://www.aulro.com/afvb/images/imported/2014/08/464.jpg

[FeatherWeightDriver]

I think you will find that on most recovery points, only the pin fits through not the bow.

My understanding is that on a connection where one side is metal, and the other is webbing, the pin should be on the metal side. But having said that I don't remember why I think that is the case, nor find anything to back up my theory so maybe someone else in the brains trust can help out...

[Blknight.aus]

Dave
If the weak link in the recovery system should ALWAYS be the pulling source, then shouldn't it read "[I]This means that every part of your system should be above its maximum limit when the winch stalls from overloading.

Nope.

Below.

If the winch stalls at 4000kg and you have a 4500kg shackle then the shackle has not reached its limit. If you had a three thousant kg shackle then when the winch hits 4000kg of pull the shackle broke because it was rated below the load out on it.

[slug_burner]

The idea is to have nothing break, everything should hold and the winch should stall.

Based on the above your red text conversion needs to be reverted to what it was.

[nismine01]

Why, when you have to pay for, carry then put it in place AND use your tow pin would you not just use your tow pin.

The end of the snatch strap goes in the pin goes through and wallah!

https://www.aulro.com/afvb/images/imported/2014/08/319.jpg

I have done that for years, I understand the dangers of pulling from the tow ball, perhaps this is just to give someone a feeling of 'right part to use'.

Dunno.

Mike :confused:

[DBT]

Why, when you have to pay for, carry then put it in place AND use your tow pin would you not just use your tow pin.

The end of the snatch strap goes in the pin goes through and wallah!


Different force will apply to the pin.

Strap-around-pin focuses the force on the mid point of the pin inside the receiver, creating a bending force on the pin. Even a wide strap eye will be deformable under load, thus transferring force to the centre of the eye strap, then to pin.

Recovery hitch places a shear force on the pin, which is what it was designed for.

I imagine the pin will not be the weakest link in either case, but if you ever bent a pin, causing it to jam inside the receiver, you'll know you came close. And have fun getting the pin out. :)

[FeatherWeightDriver]

Ignore post - still waking up...

[Islandnomad]

Thankyou for the replies, I'm getting more confused the more this continues, I've opened up a can of worms I think.


reply to Dave,
"If the winch stalls at 4000kg and you have a 4500kg shackle then the shackle has not reached its limit. If you had a three thousant kg shackle then when the winch hits 4000kg of pull the shackle broke because it was rated below the load out on it". Therefore if the winch is to be the weak point at 4000kg then all the recovery system should be stronger or above its breaking point! Otherwise I don't get what you're saying?


Further, I read on here somewhere (someone posted a letter From ARB about recovery point development) that the ARB R & D Manager says that the weak link in a recovery system should always be the snatch strap? Can't find the link for life of me. So now I'm a little confused should the weak link be, the pull source, the snatch strap, none of them all as strong as possible or the equaliser strap?


reply to Featherweight
"I think you will find that on most recovery points, only the pin fits through not the bow". I contacted APT Fabrications today they said that "All our recovery eye holes are cut at 25mm so there is easy access for the larger 4.7t bow shackles" so that the shackle can go the correct way around with the bow at the fitting and the pin at the loop. A lot of recovery points being sold have a slot not a hole for this reason.


Its pretty amazing the damage to that Patrol with just a snatch strap isn't it. Imagine if it was a shackle, and that's my point really they become potentially lethal missiles.


Recovery points rated?
As an aside I asked APT Fabrications whether their recovery points were rated he said with regards to their 8mm steering protector (which incorporates 2 recovery points) and 12mm dogleg/straight recovery points that "We’ve never had them officially rated, the engineer stated they are only as strong as the bolts used".






__________________

[FeatherWeightDriver]

Yeah it gets like that... :cool:

I agree that the weakest link in a snatch recovery should be the strap, but:
- you should not be charging so hard to ever break it and
- don't use snatch straps in winch recoveries

Re the APT comments; I will check tonight if I can turn my 4.5t WLL shackle round so the pin is out (didn't think I could but worth a look).
Unless you load the points at a severe angle the attachment bolts will almost certainly fail before the mounting brackets. Load at a severe angle is outside the intended use design envelope though, and are on your own...;)

[Islandnomad]

Thanks Featherweight will be interested to see if it can turned around too?


Its interesting to see what ARB are now producing for Toyota recover points see the current Hilux one, which is pretty heavy duty, they talk about putting the shackle the right way around too:
Recovery Points
http://www.arb.com.au/assets/thumbs/?img=/media/products/2814010.jpg&w=310&q=95Enlarge image (http://www.arb.com.au/media/products/2814010.jpg)
Recovery point

Part no: 2814010*
This recovery point is available to suit all vehicle models.

The ARB recovery point sets a new industry benchmark for how recovery points are designed, tested and selected. Rated for use with a 4.75t bow shackle and 8000kg snatch strap, drivers can safely perform a vehicle recovery while reducing the likelihood of vehicle damage. Constructed from high grade steel and featuring a long slot design for a side-angled pull, the recovery point has been specifically designed and tested for the Toyota HiLux.

Modification of under bar panels may be necessary on some vehicles fitted with an ARB bull bar.



FEATURES



Vehicle specific design, with load and destruction tests conducted on the chassis of the Toyota HiLux;
Eye constructed from 20mm high grade 350MPa steel for maximum strength and durability;
'Brace type' point permanently welded to the vehicle chassis replaces the front left cross member to radiator support brace;
Rated as part of ARB's 'recovery train' system using a 4.75t bow shackle and 8000kg snatch strap;
Unique, long slot design allows bow shackle to rotate for rated side angle up to the vehicle's maximum turn angle of the front wheels;
High tensile bolts;
Air bag compatible design;
Ideal for winching;
Easily accessible;
Compatible with fleet vehicle OH&S requirements;
Finished in a hard-wearing red powder coat for maximum visibility;
Fitting time: approx 1 hour;



And see the Landcruiser Recovery Point which is probably more relevant to Landrover people:


Recovery point

Part no: 2815010*
This recovery point is available to suit all vehicle models.

Rated for use with a 4.75t bow shackle and 8000kg snatch strap, drivers can safely perform a vehicle recovery while reducing the likelihood of vehicle damage with this ARB recovery point. Constructed from high grade steel and featuring a long slot design for a side-angled pull, the recovery point has been specifically designed and tested for the 200 Series.

http://www.arb.com.au/assets/thumbs/?img=/media/products/2815010.jpg&w=310&q=95
FEATURES




Vehicle specific design, with load and destruction tests conducted on the chassis of the 200 Series;
Eye constructed from a 20mm flame cut steel plate for maximum strength and durability;
Rated as part of ARB's 'recovery train' system using a 4.75t bow shackle and 8000kg snatch strap;
Unique, long slot design allows bow shackle to rotate for rated side angle up to the vehicle's maximum turn angle of the front wheels;
High tensile bolts;
Air bag compatible design;
Ideal for winching;
Easily accessible;
Compatible with fleet vehicle OH&S requirements;
Finished in a hard-wearing red powder coat for maximum visibility

[FeatherWeightDriver]

Nope - I can get the pin of at 4.7t shackle rotated to about 10 or 15 degrees and that's it.

You need at least double the current sized opening to get the shackle in and rotated.

[TasD90]

Hi Islandnomad, a point of clarification regarding Blknight's post.
When he says "every part of the system must be below its max. limit" he means below its OWN max. limit not below the winch's max. limit.
Hence, the first thing to reach its limit is the winch.
Cheers, Peter.

[Islandnomad]

I SEE! Thanks hahah

[Islandnomad]

I'm a little surprised about that shackle issue FeatherWeightDriver?


I think that the LRA Recovery Point is good too, it is 2 x 20mm steel zinc plated with two recovery hooks bolted to it. Does away with the shackle altogether. Can't seem to paste a photo for some reason? See link this is an earlier concept (scroll bottom) : Recovery Gear (http://www.lrautomotive.com.au/contents/en-us/d170.html)

[BadCo.]

Nope - I can get the pin of at 4.7t shackle rotated to about 10 or 15 degrees and that's it.

You need at least double the current sized opening to get the shackle in and rotated.

What about a 3.2t 19mm pin Shackle?

[Tank]

Bow or "D" shackles CAN NOT be used in any other way than which they were designed for. Quote: "Bow shackles can be pulled on almost any which way so get them." as Dave wrongly points out.
If you put a sideways pull on any shackle it will become the weakest point, you can turn the shackle around as you stated, but if you have 2 eyes of a strap on the pin of the shackle one eye will be on top of the other and unevenly loaded and could cause damage to the eyes (Friction), Regards Frank.

[Tank]

Why, when you have to pay for, carry then put it in place AND use your tow pin would you not just use your tow pin.

The end of the snatch strap goes in the pin goes through and wallah!

https://www.aulro.com/afvb/images/imported/2014/08/319.jpg

I have done that for years, I understand the dangers of pulling from the tow ball, perhaps this is just to give someone a feeling of 'right part to use'.

Dunno.

Mike :confused:
If you have a tow hitch that is straight and doesn't have a drop below centre line remove the tow ball and fit a shackle in the hole, cheaper than shown, Regards Frank.

[Islandnomad]

Frank,
I totally agree with you about only using recovery points that allow shackles to be used the way were designed, and a lot of them it seems aren't designed that well, or can only cope with a straight line recovery.


I was suggesting that for a recovery that is not in line or when you use a bridle the recovery point should be designed so that a bow shackle can be used the way its designed to be used ie the bow at the fitting and the pin at the loop.


Haven't ever considered having two loops in one shackle and one damaging the other, makes sense, but when would you ever be doing that?


Having seen the new Landcruiser ARB Recovery point above it does have a slot that allows the shackle to be used the way its designed and is 20mm thick plate. I think that it is designed as a one plate system (and not two plates and a bridle as we've been discussing) but I'd have to check with ARB.


As a result of your insight and as there don't appear to be any suitable recovery points for a D2 I'm going to ditch the shackle idea altogether. I've seen a set of Recovery Points made by Les Richmond Automotive for a D1 and D2. It is a 2 point system, also made from 20mm plate and eliminates the need for shackles. It uses those recovery hooks which bolt to the steel plates see a Hilux one that will give you the idea:

[Islandnomad]

I particularly like the way that the centre of the hook lines up with the centre of the chassis rail, good design!


This is a couple of photos from Les Richards site its a little difficult to see from the photos but I think its the best recovery point for a D2 that I've found:

[Tank]

Hooks are good, no shackles even better, only downside is hooks are back from the front and if bogged some digging maybe required to get strap eye on hook. If line of pull is above height of hook, in other words if tow vehicle is higher than the towed then you may need protective packing for strap where it contacts bottom of bull bar, Regards Frank.

[Tank]

Frank,
I totally agree with you about only using recovery points that allow shackles to be used the way were designed, and a lot of them it seems aren't designed that well, or can only cope with a straight line recovery.


I was suggesting that for a recovery that is not in line or when you use a bridle the recovery point should be designed so that a bow shackle can be used the way its designed to be used ie the bow at the fitting and the pin at the loop.


Haven't ever considered having two loops in one shackle and one damaging the other, makes sense, but when would you ever be doing that?


Having seen the new Landcruiser ARB Recovery point above it does have a slot that allows the shackle to be used the way its designed and is 20mm thick plate. I think that it is designed as a one plate system (and not two plates and a bridle as we've been discussing) but I'd have to check with ARB.


As a result of your insight and as there don't appear to be any suitable recovery points for a D2 I'm going to ditch the shackle idea altogether. I've seen a set of Recovery Points made by Les Richmond Automotive for a D1 and D2. It is a 2 point system, also made from 20mm plate and eliminates the need for shackles. It uses those recovery hooks which bolt to the steel plates see a Hilux one that will give you the idea:
I am not sure I am reading you right, but a shackle whether Bow or D shaped are designed to carry the slings (eyes) in the D or Bow section, the shackle pin is designed to be on the hook or recovery point, you will notice that ALL RATED shackles have a larger diameter pin than the body of the shackle, shackles with same size or smaller pins than the body are NOT rated and should not be used for recovery or lifting, Regards Frank.

[Islandnomad]

Really, why you can't have the bow or D against the recovery point? That's how ARB have designed their new Landcruiser Recovery Point see above, a big slot so that you can put the shackle in it and turn it around. I wouldn't have thought it would be an issue?

[Tank]

Really, why you can't have the bow or D against the recovery point? That's how ARB have designed their new Landcruiser Recovery Point see above, a big slot so that you can put the shackle in it and turn it around. I wouldn't have thought it would be an issue?
Sure you can do it that way, but eventually the sharp edges of the recovery point hole are going to damage the round section of the shackles' body with nicks and gouges, which can lead to stress fractures. Bow shackles are designed to accommodate more than one strap/sling eye, D shackles are designed to carry one strap/sling eye in the body of the shackle.
If you stack strap/sling eyes on top of one another in the confined space of the shackle pin you will damage the slings/strap eyes unnecessarily, if you are going only ever use one eye on the shackle the use a D shackle, if more than one eye use a bow shackle, Regards Frank.

[Blknight.aus]

Hi Islandnomad, a point of clarification regarding Blknight's post.
When he says "every part of the system must be below its max. limit" he means below its OWN max. limit not below the winch's max. limit.
Hence, the first thing to reach its limit is the winch.
Cheers, Peter.

Thatll do.

[Tank]

Really, why you can't have the bow or D against the recovery point? That's how ARB have designed their new Landcruiser Recovery Point see above, a big slot so that you can put the shackle in it and turn it around. I wouldn't have thought it would be an issue?
If you look at the profile shape of the recovery point hole which is flat with abrupt sharp edges, then fit a shackle you will notice that there are only 2 very very small contact points on the body of the shackle with an air gap between and underneath. Your suggestion and ARB's design is placing a round, curved bar (shackle body) against a flat, narrow (20mm) plate with 90 degree sharp edge angles. These sharp edges will damage the body and could lead to future failure.
If ARB or the purchaser sat down with a die grinder and ground away those sharp edges and smoothed them to a nice curved profile, then yes you could reverse the shackle. Good luck getting to the recovery point if you're bogged to the bull bar.
You still have the problem of 2 or more eyes (strap/slings) jambed onto the pin, if you ever have to double your strap sling up to reduce length or increase load capacity you will damage those eyes, I have seen nylon slings/straps fused together (forever) at the eyes by bunching them up this way, can be dangerous and damaging.
The pin being thicker construction (and much higher tensile strength) and straight will take to poorly designed recovery points better than the body of the shackle.
I figure that the bloke that designed Shackles knew what he was doing, he also knew the limitations and knows how they must be used and that is hook/recovery point on the pin (strongest part) sling/s in the body and load straight ahead, stick with what is proven and Fact, most of these recovery points are manufactured to a price and not a standard, how many of them are "RATED" by a Govt. test authority and are they guaranteed to perform, don't think so, play it safe, stick with your hooks or swivel collared eye bolt through the bull bar and anchored to a secure fabrication at the end of the chassis rails, Regards Frank.
Example of shackle being pulled off centre, vehicle was 100 metres away and not in line with towed vehicle and was not the tow vehicle.

https://www.aulro.com/afvb/images/imported/2014/08/309.jpg

https://www.aulro.com/afvb/images/imported/2014/08/310.jpg

[Islandnomad]

Frank,
"If you look at the profile shape of the recovery point hole which is flat with abrupt sharp edges, then fit a shackle you will notice that there are only 2 very very small contact points on the body of the shackle with an air gap between and underneath. Your suggestion and ARB's design is placing a round, curved bar (shackle body) against a flat, narrow (20mm) plate with 90 degree sharp edge angles. These sharp edges will damage the body and could lead to future failure.
If ARB or the purchaser sat down with a die grinder and ground away those sharp edges and smoothed them to a nice curved profile, then yes you could reverse the shackle". OK I do get your point and you are right. Having looked at a lot of recovery points on the market recently your point makes nearly all of them useless and full of design flaws. Good to know too! I do wonder if we are being a little purist about this, your original shackle direct pull issue that started this, exists on nearly every boat anchor I have seen, anyway your theory sounds right.


"Good luck getting to the recovery point if you're bogged to the bull bar". Isn't this the case with every recovery point as they should attach to the ends of each chassis rail? I spoke to ARB recently they told me not to snatch recover from my bulbar or attach any recovery point to it.


"stick with your hooks or swivel collared eye bolt through the bull bar and anchored to a secure fabrication at the end of the chassis rails" I'm going to go with the LRA Hook Recovery Mount sounds like the best to me 20mm plate too and does away with two shackles has to be safer. Where have you attached your swivel collared eye bolts?


"Example of shackle being pulled off centre, vehicle was 100 metres away and not in line with towed vehicle and was not the tow vehicle". Pretty scary photos Frank, and that's my point, this recovery stuff can kill and has, better to research the issues and get it right.




Further the other thing to remember with all of this, is that LR chassis rails are only 3mm thick. People say that recovery points are only as good as the bolts that attach them, well you could take it further and say they are only as good as the strength of the chassis too, see this photo I saw yesterday:

[FeatherWeightDriver]

^^^ Yikes - what part of the chassis is that? Doesn't look to be any of the factory holes with crush tubing / packing.

Back to shackles and thin recovery points - assuming the off axis loading will be not be at a large angle (e.g. 2 front recovery points used with a suitable length sling), and WLL is de-rated accordingly, looks like it is worth packing the pin to ensure the shackle stays aligned to the axis of the recovery point.

(ignore the picture on the left)

https://www.aulro.com/afvb/images/imported/2014/08/258.jpg

[Tank]

Frank,
"If you look at the profile shape of the recovery point hole which is flat with abrupt sharp edges, then fit a shackle you will notice that there are only 2 very very small contact points on the body of the shackle with an air gap between and underneath. Your suggestion and ARB's design is placing a round, curved bar (shackle body) against a flat, narrow (20mm) plate with 90 degree sharp edge angles. These sharp edges will damage the body and could lead to future failure.
If ARB or the purchaser sat down with a die grinder and ground away those sharp edges and smoothed them to a nice curved profile, then yes you could reverse the shackle". OK I do get your point and you are right. Having looked at a lot of recovery points on the market recently your point makes nearly all of them useless and full of design flaws. Good to know too! I do wonder if we are being a little purist about this, your original shackle direct pull issue that started this, exists on nearly every boat anchor I have seen, anyway your theory sounds right.


"Good luck getting to the recovery point if you're bogged to the bull bar". Isn't this the case with every recovery point as they should attach to the ends of each chassis rail? I spoke to ARB recently they told me not to snatch recover from my bulbar or attach any recovery point to it.


"stick with your hooks or swivel collared eye bolt through the bull bar and anchored to a secure fabrication at the end of the chassis rails" I'm going to go with the LRA Hook Recovery Mount sounds like the best to me 20mm plate too and does away with two shackles has to be safer. Where have you attached your swivel collared eye bolts?


"Example of shackle being pulled off centre, vehicle was 100 metres away and not in line with towed vehicle and was not the tow vehicle". Pretty scary photos Frank, and that's my point, this recovery stuff can kill and has, better to research the issues and get it right.




Further the other thing to remember with all of this, is that LR chassis rails are only 3mm thick. People say that recovery points are only as good as the bolts that attach them, well you could take it further and say they are only as good as the strength of the chassis too, see this photo I saw yesterday:
I did say to fabricate a box section that either fits inside or outside of the chassis rails, bolt or weld this fabrication to the chassis, the forward facing plate, 1/2" thick with a nut and thread (in 1/2" plate) to suit the collared eye bolt.
This plate which is secured (welded) and the boxed in fabrication in the chassis take the thread of the eye bolt, the bull bar only has a hole to allow the eye bolt to pass through to the plate on the end of the chassis rail. The collar of the eye bolt butts against the front face of the bull bar, the bar takes no load so isn't compromised.
To make the plate that the eye bolt attaches simply weld the appropriate nut to the 1/2" plate, drill the correct size hole and tap through the nut and now joined plate, you should have at least 1" of thread for the eye bolt, then you can put a hardened washer on the end and fit a Nyloc nut.
Recovery points for under the front of chassis, except for the hook type, and remember a hook will never be as strong as a full loop, are designed/thought up to be easy and cheap to manufacture, no thought has been given to the consequences of their use, here's a test using anyone of these flat plate recovery points, loop a piece of Dyneema, nylon or fibre rope through the pin hole and attach to a load and back up, I'll bet it cuts through as soon as you get some weight on it. The steel body of a shackle will not cut through, but it will have nicks/cuts where the sharp edges dig in. those nicks and cuts can lead to stress fractures which could cause failure down the track.
Getting under to connect a shackle or strap when bogged is not fun and sometimes not possible, also have seen straps cut through by the bottom of bull bar trapping underslung sling on a hard rock, BTW you don't have to mount recovery hooks under the chassis, what's stopping you from mounting on top.
I believe that no recovery point should be mounted to the front of the chassis rail UNLESS it is reinforced or boxed internally or externally, lot of work, but you won't be tearing bull bars or ends of chassis rails off, good luck, Regards Frank.

[workingonit]

Better than typing a lot...

See link, particulary 'calculating the force of a recovery' about quarter way down - don't know how valid calcs are but food for thought.

Pirate4x4.Com - Extreme Four Wheel Drive (http://www.pirate4x4.com/tech/billavista/Recovery/)

[Islandnomad]

Wow Frank, that is a lot of work! Not within my skillset. Like to see some photos though. Most of the recovery points I've seen are designed for the straps to go under the bull bar (never seen one cut off), never thought of going through it. It sounds to me like this stuff should be done by the bull bar manufacturers when they fit the bar. I certainly don't have the ability to do that, wonder who would, cost a fortune for my mechanic to do it? mmmmm interesting!

[philco]

Hooks are good, no shackles even better, only downside is hooks are back from the front and if bogged some digging maybe required to get strap eye on hook. If line of pull is above height of hook, in other words if tow vehicle is higher than the towed then you may need protective packing for strap where it contacts bottom of bull bar, Regards Frank.

Our Gold Coast Club do not recommend the use of hooks to any of our members.

[Islandnomad]

Great article workingonit! It certainly reinforces what you're saying Frank.


Philco I thought that recovery hooks were a good idea because they eliminate the need for shackles, they are rated at 4500kg each and they bend rather than break, so they are safer. Why doesn't your Club recommend them?

[FeatherWeightDriver]

Better than typing a lot...

See link, particulary 'calculating the force of a recovery' about quarter way down - don't know how valid calcs are but food for thought.

Pirate4x4.Com - Extreme Four Wheel Drive (http://www.pirate4x4.com/tech/billavista/Recovery/)

Definitely food for thought!

Another good link, especially talking about Defender recoveries is: Vehicle Recovery Points And some technical aspects*********************Â  ******** by Mike Lauterbach (http://www.landroverclub.za.org/vehicle_recovery_points.htm)

Again I'm not in a position to validate the numbers, but worth thinking about...

[Islandnomad]

Another interesting article Featherweight! He mentioned Jate Rings which utilise the existing reinforced chassis points on D2's and are attached with 8.8mm rated zinc bolts? He indicates that "A jate ring, or similar attachment can be attached to the horizontal bolt in the lower section. Again, the applied force should be limited to 4 tons per side". This is probably going to be the answer, its simple, and you can pull on them on an angle with a shackle! The towbar recovery point at the other end only rates to 4.75 ton as does its shackle. There are 2 types, 3.25 inches wide and 3.75 inches wide. They only cost $44 US each plus freight see link http://www.landroverstuff.com/prodjate.htm. I believe the Military have been using them for years too. Any opinions on these?


Also see photos:

[Tank]

Our Gold Coast Club do not recommend the use of hooks to any of our members.
First time you have ever replied to me, I have posted PM's to you asking why your recovery points don't allow the shackle to orientate itself to the line of pull, which could be made possible if your recovery points had the shackle pin hole in the vertical plane rather than the horizontal.
I know it is easier to stamp or profile cut your recovery points, but a bit of heat and some twisting or forging could align the pin hole correctly.
I would prefer to use a hook, esp. on top of the chassis rail than a bit of plate bolted to the side of the chassis rail, some distance back from the bull bar.
If a hook straightens out it will not have a recovery point and shackle attached travelling at supersonic speeds towards another vehicle or person, Regards Frank.

[Tank]

Better than typing a lot...

See link, particulary 'calculating the force of a recovery' about quarter way down - don't know how valid calcs are but food for thought.

Pirate4x4.Com - Extreme Four Wheel Drive (http://www.pirate4x4.com/tech/billavista/Recovery/)
Workingonit, good article, in Australia the use of "Bulldog Clamps" on working cables are totally banned, they may be used on Standing Rigging, such as Guy Wires as used to hold up tall masts that don't move. I have seen bulldog clamps used on tow trucks and 4WD winches, they are prone to slip under load and they decrease the SWL/WLL of any cable they are applied to. Will get you out of trouble if you break a cable, but make sure if you use them to have the "U" bolt loop on the tail of the cable. Good clamps have the profile of the cable in the body of the clamp, which always goes on the lead part of the cable, to give better grip.
The only other thing I noted was that the article didn't mention that 6 strand rope core wire cable should not be used on a winch or run over a sheave (snatch block) as it will crush flat and damage the cable, only 7 strand wire with a wire core should be used on a winch/sheave/tirfor, would have liked to have seen formulas for determining SWL of wire cables, I use the Dia. squared (in mm) x 10 and add 12% for wire core cable, Regards Frank.

[Meken]

So how do we work out the load when a snatching vehicle accelerates off and takes up the slack? Are there different loads at play between a slow winch increasing the load on the rope until say 3 x LW to get a vehicle moving off its belly compared to the snatch recovery - my old maths II school brain says Force (F) = Mass(M) x acceleration (A). So in each recovery the mass remains same (say 3t for loaded disco) but the acceleration in a winch recovery is much lower - so in old mates theory of 1x, 2x, 3x LW depending on the degree of stuck, then if you say the acceleration in a snatch recovery is 2x that of a winch recovery the force could be 6x LW (18t) ?

[Meken]

Here we go I found an answer for my question, interesting tables of test results of snatch straps about middle to bottom of page ... Super cheap straps by name....

http://www.landroverclub.za.org/snatch_straps.htm

[FeatherWeightDriver]

^^^ Yep - charge in to a snatch recovery like a wounded bull and the forces get REALLY big REALLY fast.

Interesting point in that article about how long a snatch strap takes to get is springiness (or stretch) back...