Thread: Recovery System Design HELP and the Weak Link

Originally Posted by 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?

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.

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:

^^^ 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)

Originally Posted by 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:

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.

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

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!

Originally Posted by 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.

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

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?