Terranosaurus
Well-known member
- Joined
- Aug 16, 2006
- Messages
- 3,991
Thought a quick guide to recovery equipment might be useful.
So how strong should stuff be.
Theres no set safety factor ratio for recovery work but personally I like to work on 2:1. But first we need to know the forces involved.
On dry tarmac rubber has a friction coefficient of 0.7-0.8 this means that a 1 tonne vehicle can exert 0.7-0.8T force through its tyres. So if we take a fully loaded defender 110 at 3.5T it can exert 2.8T max (using 0.8 as worst case).
How about winching. Well if you can anchor yourself to a big tree or rock then you an exert the full force of the winch so say 12000lb or about 5.5T.
On this basis I work on a minimum of about 11T (2 x 5.5T) breaking strain.
Weak link.
There will always be a weak link the trick is to choose what it is. If a shackle breaks it splinters and shrapnels flies around. If a wire winch rope snaps it recoils dramatically and can cut through flesh and bone. f a strap snap it has next to no recoil and will act as a sail to any wire rope it is attached to and this slow te recoil.
So always make a strap the weakest link.
Other Stuff
Waffle boards can be useful as can a high lift jack etc.
Last point
You don't need all this gear to enjoy yourself. A simple strap and a shackle or 2 means you can get out of most trouble you'll ever get into and there will always be someone else around to help, especially if you come along to a N&FM4x4OC green laning trip. So don't rush out and buy loads of gear, come along a few times and see whats, what first.
*more on Kinetics
There will be people reading this that think rubbish they are safe etc.
Kinetic recovery was developed for recovering tanks - they are amoured 4x4s are not.
As you will see above it is possible to quantify the maximum pssible forces involved in conventional and winch recovery. Unless you know the precise elastic qualities of a knietic strap/rope, the weight of the free vehicle and its precise speed and are very good with maths you cannot even begine to estimate the forces involved. The reason people think they are so good is the very reason they are dangerous - ie the high forces involved. OK off my soapbox now.
First strap a 4.5m is a good idea. Thats the max legal legth for towing - breaking strain wants to be minimum 10T - thats roughly twice what a 12000lb winch can pull if you ever use it in conjunction with a winch.
Shackles should be rated - 3.25T is a good start, 5:1 factor means over 17T breaking strain, and also the go through the rear recovery points.
A shovel - obvious uses really and very usefull.
After that it really is horses for courses, you'll learn wat you need as you go along. Shackles should be rated - 3.25T is a good start, 5:1 factor means over 17T breaking strain, and also the go through the rear recovery points.
A shovel - obvious uses really and very usefull.
Bridle - 3m long with reinforced centre is usefull to spread the load down both chassis legs, prevents twisting the chassis.
A Long strap 8 or 10m is usefull to get you onto solid gound to pull from.
Short ones can be handy too but can always double up a longer one (or even triple)
Tree savers should be wide - obviously - 2-3m - only need these if you have a winch though.
Ratchet straps should be used for securing loads only.
Rope - good for towing but IMHO shouldn't be used for recovery unless you truely know the breaking strain of it.
Kinetic Recovery Ropes/Straps - personally I wouldn't touch em. Its impossible to quatify the loads involved and if somethig breaks they can be quite literally lethal. If you're that stuck you should't be on a green lane cos you shouldn't be driving tem in that condition, so that means you're at a ay and play site or simialr. There'll be someone there with a winch ask them for asistance. * see below for more....
Breaking Strain, WLL, SWL and all that.A Long strap 8 or 10m is usefull to get you onto solid gound to pull from.
Short ones can be handy too but can always double up a longer one (or even triple)
Tree savers should be wide - obviously - 2-3m - only need these if you have a winch though.
Ratchet straps should be used for securing loads only.
Rope - good for towing but IMHO shouldn't be used for recovery unless you truely know the breaking strain of it.
Kinetic Recovery Ropes/Straps - personally I wouldn't touch em. Its impossible to quatify the loads involved and if somethig breaks they can be quite literally lethal. If you're that stuck you should't be on a green lane cos you shouldn't be driving tem in that condition, so that means you're at a ay and play site or simialr. There'll be someone there with a winch ask them for asistance. * see below for more....
Breaking strain is pretty obvious its the force needed to break something.
WLL - Working Load Limit, SWL - Safe WOrking Load. Essentially these ae the same thing and come from lifting. In lifting straps have a 7:1 safety factor built in and shackles have a 5:1 safety factor.
WLL - Working Load Limit, SWL - Safe WOrking Load. Essentially these ae the same thing and come from lifting. In lifting straps have a 7:1 safety factor built in and shackles have a 5:1 safety factor.
So how strong should stuff be.
Theres no set safety factor ratio for recovery work but personally I like to work on 2:1. But first we need to know the forces involved.
On dry tarmac rubber has a friction coefficient of 0.7-0.8 this means that a 1 tonne vehicle can exert 0.7-0.8T force through its tyres. So if we take a fully loaded defender 110 at 3.5T it can exert 2.8T max (using 0.8 as worst case).
How about winching. Well if you can anchor yourself to a big tree or rock then you an exert the full force of the winch so say 12000lb or about 5.5T.
On this basis I work on a minimum of about 11T (2 x 5.5T) breaking strain.
Weak link.
There will always be a weak link the trick is to choose what it is. If a shackle breaks it splinters and shrapnels flies around. If a wire winch rope snaps it recoils dramatically and can cut through flesh and bone. f a strap snap it has next to no recoil and will act as a sail to any wire rope it is attached to and this slow te recoil.
So always make a strap the weakest link.
Other Stuff
Waffle boards can be useful as can a high lift jack etc.
Last point
You don't need all this gear to enjoy yourself. A simple strap and a shackle or 2 means you can get out of most trouble you'll ever get into and there will always be someone else around to help, especially if you come along to a N&FM4x4OC green laning trip. So don't rush out and buy loads of gear, come along a few times and see whats, what first.
*more on Kinetics
There will be people reading this that think rubbish they are safe etc.
Kinetic recovery was developed for recovering tanks - they are amoured 4x4s are not.
As you will see above it is possible to quantify the maximum pssible forces involved in conventional and winch recovery. Unless you know the precise elastic qualities of a knietic strap/rope, the weight of the free vehicle and its precise speed and are very good with maths you cannot even begine to estimate the forces involved. The reason people think they are so good is the very reason they are dangerous - ie the high forces involved. OK off my soapbox now.
