Another snatch strap death

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Originally Posted by tact

- in a tow recovery typically the limitations of traction available to the recovery vehicle (ground surface and tyre interface) is what will ultimately cap the level that recovery forces can reach. Typically much lower than winch or snatch. Of course a gutless towing vehicle will further lower the level of force that can be reached - but assuming the tow vehicle is powerful enough, its where the rubber meets the road/gravel that caps forces on the tow equipment.

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If a recovery vehicle is on level ground with good friction such as asphalt or bedrock, then according to the laws of dry sliding friction, when conducting a static tow it will be able to generate approximately as much force as its own weight. So if its a 3t vehicle it will be able to generate approximately 3t of pulling power. If its an unladen suzuki sierra it will be able to generate approximately 1t of pulling power.

The amount of engine power of the towing vehicle in this situation is not a significant factor, although the strength of the clutch may play a role, if say the tow vehicle is overloaded and hence can generate higher loads on the clutch.

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Originally Posted by rammypluge

All things fail in shear, but when a bolt is loaded under tension it will fail in a cone shape, so the shear area is larger than if it fails under pure shear. The larger shear area means more force is required.

However, is the bolt actually under pure shear? Can you rule out any element of bending load?

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??
The point was that a bolts strength in shear is lower than the rated tensile load.

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Originally Posted by rick130

??
The point was that a bolts strength in shear is lower than the rated tensile load.

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Sure, but how exactly is the bolt that attaches the tow point loaded?

Will side loading of the tow point change the loads on the bolt?

Apparently several here never push their vehicles into locations where simple recoveries are not the order of the day.

My recovery kit at work has things like 70t rated recovery rope. [emoji41]

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Originally Posted by Tombie

Apparently several here never push their vehicles into locations where simple recoveries are not the order of the day.

My recovery kit at work has things like 70t rated recovery rope. [emoji41]

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So what sort of recovery gear did you have on your D2 and what is on your D4?
Apparently some of us here are not stupid or drunk enough to go places where 70T recovery gear is needed because we have too much respect for our vehicles and we Know their limitations. [bigwhistle]

The vehicles limitations are actually quite different compared to many users capabilities. Many will pull out long before the vehicles ready to give up!

And obviously you can’t differentiate a comment on experience rather than vehicle specific - I haven’t driven the D2 for years for example - I just maintain it nowadays.

But as you asked:
2 snatch straps
2 winch extension straps
2 tree trunk protectors
2 Snatch blocks
6 Shackles (Green Pin)
Drag chain
50m of synthetic winch rope on winch
Spare winch rope.
500mtrs of 12mm dyneema
Ground anchor
2 bottle jacks
2 Jacking plates
Rated recovery points front and rear fitted using engineer approved mounts.
Long handled shovel
Recovery boards


On the work rigs which work in raw areas, wet areas, mud, dirt, molten environments..
I carry 70t recovery gear... and bring in equally large gear to attach it to...

Quote:

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Originally Posted by rammypluge

Sure, but how exactly is the bolt that attaches the tow point loaded?

Will side loading of the tow point change the loads on the bolt?

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I really didn't want to get into double shear with a nice straight load path vs single shear, I just wanted Martin to realise that a bolt in shear didn't have the same load rating as a bolt in tension.

Most recovery points are mounted in single shear and will have a bending component in most recoveries and so the bolts needs to be derated accordingly, although I've seen some swivel type points mounted in tension on the front of a Deefer.
This is where the Poms love of using JATE rings on Defenders work, even though they aren't rated for recovery

Of course many of us don't venture into areas that we know from experience that ordinary recoveries won't work because we choose not to and many of us travel solo as well.
I and many other also can't see any point in pushing our vehicles to their very limits and risking destroying/damaging the running gear or even loosing the truck entirely, Not to mention the safety risks to ourselves and/or our passengers.
If people have to go to these sorts of places due to work Or they simply enjoy that sort of thing then that's up to them But when they expect others to recover them then that is quite a different thing.
When myself and the Missus travel anywhere we take 2 4WD vehicles She tows the van and I tow the boat so that IF we do get into difficulties we have a far better chance of getting out of them without relying on others help.
Between us we carry
2x bottle jacks and planks for baseplates.
1x highlift jack that we hope to Never have the need to use.
4x snatch straps that we have chosen not to use yet.
2x 20m extension straps
30m of 13mm dyneema on the winch
2x spare 30m 13mm dyneema winch ropes, We have used these as extension straps on occasion.
2x trunk protectors
1x drag chain
2x snatch blocks
6x 4.7T rated bow shackles
2x long handled shovels
6x "Treads" recovery boards
If you spread these things between two vehicles they are not that much trouble to fit in.

Usually we have absolutely No need of these things But on a few occasions they have come in very handy for ourselves But usually for recovering other people that have overestimated the capability of their vehicle/themselves or have simply done something stupid like not lowering their tyre pressures enough and have got themselves well and truly stuck.
If I consider any recovery to be too dangerous or it will damage mine or someone else's vehicle I will abort it in favour of a tow truck or tractor/grader to pull them out.

I Never deliberately go into areas that I know that I will get horribly stuck anymore because I don't particularly enjoy the recovery process and the work involved doing it, I would much rather spend that time fishing and will leave the playing "Silly Buggers" to the young blokes.

I would think that most difficult recoveries are caused by inexperienced and or reckless people. Experienced, level headed people can go to extreme places and do extreme things, but mostly avoid major screw ups. If it does happen, then they should be pretty decent at sorting the dilemma without copping a missile in the head.

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Originally Posted by rammypluge

I would think that most difficult recoveries are caused by inexperienced and or reckless people. Experienced, level headed people can go to extreme places and do extreme things, but mostly avoid major screw ups. If it does happen, then they should be pretty decent at sorting the dilemma without copping a missile in the head.

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Yep. I have plenty of images that I’m unable to post of heavy recovery.