Thread: Recovery System Design HELP and the Weak Link

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!



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

Originally Posted by 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!

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.

Ignore post - still waking up...

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".






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Yeah it gets like that...

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...

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
Enlarge image
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.


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

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.

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.