Thread: Rotating recovery points. Comparison and pricing.

Dare I ask, what magnitude of load would be put on those points? It seems to me these points are rated for lifting purposes. Should one apply a factor to the SWL and WLL when used in a recovery situation?

Also, I assume the ratings displayed are for predominately vertical lifting. What would be the effect with angular lifting be? I have seen a few recoveries where it was not possible to pull the vehicle straight out.

The 24mm are rated for WLL 4tonne, lifting, so thats a 5:1 safety factor and MBS is still greater than WLL. So 20t design essentially downgraded for wear, tear & numpty factor.

Excellent question Mick...

With the 5:1 safety factor - I have run the 24mm VLBG versions which gives me 4t WLL = 20t failure. With a 3.2t shackle = 16t and using 2 mounts and a bridle (12t breaking strain) and an 8t snatch strap - this means the strap will let go long before any metal will start flying about.

I use the VLBG version because they dont rattle when not in use..
You can see the working angles in the image (and they self align)



Whilst we are at it... Some data on using a shackle side loaded... (knew I had it in a manual somewhere)

Using a shackle with the commonly available recovery points that have been the topic of much debate in recent times....

IF a shackle is used at a side loaded angle the following is to be taken into account:





So, what does it all translate to?

With a 3.2t shackle you have 16t before yield.
With a 4.7t shackle you have 23.5t before yield.

At 45 degrees you have a reduction of 30% SWL
a 3.2t shackle becomes a 2.24t shackle with yield at 11.2t
a 4.7t shackle becomes a 3.29t shackle with yield at 16.45t

Lets put it into practice:
Using an appropriate sling (bridle) of sufficient length to maintain angles under 45 degrees, you would be wise to consider using 4.7t shackles to attach to your recovery points (for the additional rating) - although 3.7t shackles are still rating higher than the 8,000kg (fail load) snatch strap they are inline with...


Now for an example of where horizontal / vertical alignment goes out the door...

Guess which way the shackle would be loading!!!

Originally Posted by Mick_Marsh

Dare I ask, what magnitude of load would be put on those points? It seems to me these points are rated for lifting purposes. Should one apply a factor to the SWL and WLL when used in a recovery situation?

Also, I assume the ratings displayed are for predominately vertical lifting. What would be the effect with angular lifting be? I have seen a few recoveries where it was not possible to pull the vehicle straight out.

in the lifting world ideally you use chains of the same rate as thelifting point, as you work down SWL by means of the angle on the chain you're automatically taking the degrade on the point into account.

the last time I was selecting lifting fittings for fitment to a container the available lifting points had a chart that indicbated the angles you could use them at as a simple black and whie go/no go diagram, if you were in the white you could putt your max rate on them, if you were in the black you werent to use that fitting.

a good example of this is in disco muppets post here the ones on the white disco i remember as having a full 180 degree loading arc within a full 360 degree rotation. the ones as fitted to the front of lara had about a 60 degree arc (30 degrees either side of perpendicular) and a full 360 degree rotation.

edit

but for the want of a little patients on my behalf..
tombies previous post has a colour diagram of what I was talking about for the white disco points...

and the diagram of the shackle highlights what I was saying about the lifting point derating with the chain angle. Imagine 2 shackles used to hold a bridle strap to the front of the vehicle. IF the chain and the shackles had the same SWL as the angle used in the formula went up the calculated WLL for the chain would go down. The derate has already taken the angle on the liting point (in this case the shackle) into account. This is one o the diferences between the lifting orld and the recovery world.
in the recovery world its easy to side load a single shackle. Thats harder to do in the lifting world as gravity tends to make everything hang in a nice line when you only have a single lifting point

Thanks, Tombie, just the information I was after.

Last few questions.
Do all snatch straps snap at 8t or can you get them at different ratings?
Assuming the vehicles are about 4t, what sort of force would typically be on a snatch strap? 1.5 times? 2 times?

Snatch straps are available in a range of sizes with 8000 and 11000 being common but some brands go up to 16000.

I just looked at the Just Straps website and they also give a Recovery Load Limit.

Originally Posted by Mick_Marsh

Thanks, Tombie, just the information I was after.

Last few questions.
Do all snatch straps snap at 8t or can you get them at different ratings?
Assuming the vehicles are about 4t, what sort of force would typically be on a snatch strap? 1.5 times? 2 times?

Snatch straps come in all different sizes, I have 11000kg straps in the Disco/RR/Cruiser, and on the farm I have a 40t strap for pulling out the header with the New Holland.

I have read that a general rule is 3x the mass of the vehicle, but it varies with each strap and it's elasticity.

I think the thing with a snatch strap, as opposed to a tow or winch extension strap, is to not go over the top with rating or you loose the benefit of the elasticity. And probably induce all sorts of shock loads to other fittings in the recovery set up.