Recovery - The Fundamentals

thanks again Nic for taking this on - it is pretty impressive

thanks guys very helpful:)

Thanks, thought provoking and informative.

What about explanining basic 3 to 1 adavantages, or about spliting your load , instead of pulling 1 ton why not only pull 1/2 ton

Quote:

Originally Posted by benmatters

What about explanining basic 3 to 1 adavantages, or about spliting your load , instead of pulling 1 ton why not only pull 1/2 ton

If you go back to the first page and have another look you will find the answers are there, also the top of the second page posted by EvilTwin also addresses mechanical advantage in basic maths.

Here is a couple of exerts

Quote:

Originally Posted by MudRunnerTD

Snip.

Basic Winching and the Affect of Slope.

Winching on flat ground in a straight line is pretty well as safe as houses as long as you adopt safe work practise. The load is well within the ratings of the equipment on every 4WD. But who does that?

Standing clear, Using a Winch Blanket and connecting to a Rated Recovery Point on the vehicle is all that should be needed to extract the vehicle.

How much are you really pulling up that hill when you are swing off a winch cable on a 30Degree slope? And what about when you are bogged to the axles or sitting on your belly in the mud? Sticky Otways Mud?

What if you have to winch around a corner? How do you do that?

There are basically four different types of resistance that you will encounter while off roading that affect the load on the winch. These include:

1. Surface Resistance.
2. Slope Resistance.
3. Bog Resistance.
4. Damage Resistance.

The figures below come from extensive reading and research and a dash of commonsense. As explained earlier, there is no comprehensive list of regulations for recovery that contain this information.

To move or pull a 4WD on a firm flat bitumen surface requires a force of just 10% of the loaded weight of the vehicle. To do the same on gravel or grass increases this to about 33% of the loaded weight of the vehicle.

Throw an incline in and that maths increases significantly.The percentages need to be added to the loaded weight and can change things dramatically and quickly increase the weight being recovered to far beyond the capacity of the equipment.

For an Incline, or Up Hill, the following extra weight should be added to the loaded weight of you vehicle as a guide:

• 15degree Slope == add +25% of the loaded weight

• 30degree Slope == add +50% of the loaded weight

• 45degree Slope == add +75% of the loaded weight

On flat ground no change is required

For a Decline, or Downhill, the following weight can be deducted from the loaded weight of you vehicle as a guide:

• 15degree Slope == subtract -25% of the loaded weight

• 30degree Slope == subtract -50% of the loaded weight

• 45degree Slope == subtract -75% of the loaded weight

Basic Winching and the Affect of MUD.

But what if your bogged? If your fourby is bogged in the Mud then the depth of the bog will have a massive affect on the loaded weight of the vehicle.

Below is a guide only for calculating the dead weight of the vehicle when in mud.

Bogged to the Base of the Wheel Rim, you will require a pull of 100% of the load

Bogged to the wheel Hub, the weight doubles! You will require a pull of 200% of the load

Bogged to the Belly or the Chassis and it is x3! You will require a pull of 300% of the load

And lets face it, the later is when winches are really being asked for.

Apply these weight variants to ALL of your RECOVERY gear!

Consider these variations when you are looking at your vehicle and considering how you will extract it form its position. Consider being stuck in the mud to the chassis on a 25degree slope!!!

Pounds Vs Kilograms – the Real Story.

Why do we have winches on our vehicles that quote the mass weight strength of the line pull in Imperial Pounds when we are living in a Metric System of Measure.

It because the bench mark brands of winches originate in the USA where it is all about pounds.

And lets face it 8000lbs sounds much tougher than 3600kgs! Imagine the Warn High Mount called the 3.6.

Get to know your gear and get to know it in the Metric world. Do the conversions and document them in your vehicle if you cant remember them. Send it to yourself as a text message on your phone so you never forget. This will save your life.

For the record - 1lb equals 0.454kgs, or 1kg equals 2.2lbs.

8000lbs = 3632kgs
9000lbs = 4086kgs
10,000lbs = 4540kgs
12,000lbs = 5448kgs

Scenario

So, your average GU Patrol for example has a loaded weight of 3.3t (2.2t tare by 1.5t). Your stuck to the chassis, so you will need to pull 9.9t out of the muck (3.3t x 300%)

Throw on a camper trailer (1t) and your Nissan’s winch and recovery gear needs to deal with 12.9t!

Now look at the list above and see the problem you are in!!

Snip

Quote:

Originally Posted by MudRunnerTD

Enter the Snatch Block!

An introduction to the Power of the Multi-Line-Pull.

We’ve just worked out that, by itself, your winch is in big trouble. The electric winch has many limitations and is not the be all and end all. By itself it is very handy and will give many an inexperience four-wheel driver a false sense of security and confidence and can get you into more trouble than it can get you out of if in the wrong hands.

This is why we like to use the humble Snatch Block. You cant have too many of these. If every one has one then you may have many on a hill. This is all good.

The snatch block is a rated piece of equipment that allows the cable to run over a pulley and change direction too another tree or back to the winching vehicle.

The awesome power of the Snatch Block is that as soon as you introduce a pulley within the line you HALVE the weight on the line!! Add 2 Snatch Blocks and you reduce the weight to 33% of the line weight at the hook!

Add Three? Well, then you will reduce the load on the winch to 25% or so of the load on the hook. This is called a Triple Line Pull. It is slow but very effective.

Remember, every time you add a Snatch Block you reduce the weight significantly, but also reduce the speed of the winch but double the power so who cares.

**Very Important.. The mathematics that we have set out here is only true if the pulley is set up to allow the pulley wheel to turn with the cable.

The Weakest Link

**Very Important

Remember that the main reason that we introduce Snatch Blocks is to halve the weight on the winch effectively allowing us to pull far in excess of the pulling power of the winch.

Often when Snatch Blocks are introduced the winch line is used up in the double or Triple line pull and we have to use a Winch Extension Strap. What is the rating of this strap?? The more Line pulls the more likely that you can introduce a weight beyond the breaking strain of the strap. This is very easy to do and it is disastrous.

Massive loads are placed on your recovery system when introducing Snatch Blocks; so think about all of it every time you use it, when ever you pull it out and after you pack it away!

The Final Check List

1. Is your recovery Hook rated and to what level?

2. What is the breaking strain on the Winch Extension Strap?

3. What about the Tree Truck Protector?

4. The Shackle?

5. What does my Winch cable look like?

6. What does it look like now?

7. Did I pack it away and re-spool it properly?

8. Have I lubricated it?

9. Is that winch cable that I will hang off one day just a rusty Birds nest on the front of the vehicle or re-spooled and lubricated ready for use?

10. Have I put any of my gear under extreme load before? And should it be replace?

Rule Number 1

Work Safely, Protect Life.
Determine the load,
Assess the Environment.

THINK!!

Enjoy the drive, Tread lightly

Special thanks to Australian 4WD Action for being a great Resource

Cheers MudRunnerTD
AKA Darren

Quote:

Originally Posted by the evil twin

Firstly, what a great Post Darren,

I am also a Driver Trainer and Rescue Systems Instructor with the S.E.S. which brings a heap of personal satisfaction which I am sure you get as well doing similar with your Club.

If I may be permitted to make an observation in the interests of accuracy tho. The figures for two snatch blocks IE triple line pull are incorrect. A standard triple line pull provides a 3:1 mechanical advantage not 4:1 reduces the load on the cable to 1/3rd not 1/4.

25 Degrees = Load (2,800kgs) + 45% = 4,060kgs X 300% for mud = 12,180kgs
PLUS the wieght of the Organic mass out the front (About 3m3) and we were up around the 15,000kgs!!

Put in a Snatch block and that is halved to 7,500kgs, and what is the Hi Mount rated at? 3,632kgs!
Should have done a triple line pull...Even a Triple Line pull would be 3,250kgs!,

In that example the "triple line pull" cable load will be 1/3rd or 5,000 Kg's hence the "triple" in the M.A. rig name.

Whilst on the subject... There is one other factor in M.A. rigs for everyone to keep in mind as well, the load on the snatch block is the sum of the loads on the cable so again to use the same example whilst the load on the cable is 5,000 Kg's the load on the strap or shackle securing the snatch blocks to the vehicle and tree (or whatever) is 10,000 Kg's.

Here is a cracking good article on M.A. Rigs and loads to illustrate.

Figure 7 Rig C shows a standard or "triple" line pull 3:1 M.A. rig most people are familiar with and utilise (2 Snatch blocks, 3 anchors)

Figure 8 Rig A shows how to get a 4:1 M.A from only 2 Snatch blocks and 3 anchors with the lowest load on the Shackles and Rigging using a compound rig which would indeed reduce the line load to 3,750 KG but is no longer a "triple pull". This method needs another rope or cable tho for the 2nd 2:1. In my case I carry a length of Dyneema for this and other uses.

http://www.ncstaff.net/oed/Pulley%20MA%20Systems.pdf

Again, my compliments on a top shelf amount of info. The more we get the info out there and the simpler it is then the safer it is for everyone and hopefuly the tragedies will diminish

Hey Ben i hope the posts above clarify and fill the gaps you were trying to address. All good mate and i appreciate this thread getting bumped as often as you like.

Stay safe this Easter.

Cheers MR

Wow so wot winch systems and gear would you recommend?

Ok yes so all that stuff about degreases is good, some basic load sharing should be placed in hear for example if I was to pull a load that was 100kg and used a simple 3 to 1 I would be only pulling 1/3 of the load there for the load on my gear would only be a 1/3

I do not mean to be backward, I do understand what you have posted before, but I cannot stress how important it is to fully explain your advantages in say a 3 to 1. A lot of people just don’t understand, I do not know how to post diagrams to explain this but I was hopping you could. Just remember there are a lot more than just your basic 3 to 1, these things need to be illustrated so people can fully understand how they work.

Quote:

Originally Posted by benmatters

I do not mean to be backward, I do understand what you have posted before, but I cannot stress how important it is to fully explain your advantages in say a 3 to 1. A lot of people just don’t understand, I do not know how to post diagrams to explain this but I was hopping you could. Just remember there are a lot more than just your basic 3 to 1, these things need to be illustrated so people can fully understand how they work.

I appreciate your input Ben, i have tried to address the 3:1 ratio and the use of a Snatch Block in the post above at the start of the second Snip.

I Highly Recommend that everyone clicks on the link provided by EvilTwin and scroll down to about page 6 where it starts to get really interesting. There are some great pics on page 8

Check it out here Power of the Snatch Block

Quote:

Originally Posted by Dr Gary

I noted advice on keeping winch cable lubricated. No data on that from Warn, so can you help with the type of lube recommended. I have a mudflap rubber "skirt" covering the front of the winch, hopefully to keep some of the crud out.

Mine -- WD 40 twice a month (when not in use), when in use (wash, dray - watch out the fingers for the split pieces on cable) then any kind of oil can do the job