Understanding loads and selecting the right winching equipment

[David Dobedoe]

I am in the process of understanding and selecting winching equipment. I want to ensure that the equipment I put together is all compatible and fits in with best practice guidelines. Ultimately I can see several sets of equipment being helpful given the different sizes of challenges winches can be applied to.

 

I am considering the Tirfor with a working load limit of 1600kg. I understand that this winch is designed to fail at 50% overload via a shear pin. This should mean that the pin fails at 2400kg. Is this correct?

 

As I understand it strops, shackles and pulleys are designed to fail at 400/500% overload. For example a 2000kg strop in good condition and used 'sensibly' shouldn't fail before its loaded to approximately 8000kg. Is this correct?

 

Given the redundancy (reserve strength) in the pulleys/strops and shackles etc.) is a much bigger margin is it considered acceptable/good practice to put together 'sets' of kit together based on the redundancy or not?

 

The winch obviously gives a mechanical advantage. When a more powerful pull is needed it is possible to use pulley systems. I have some concerns about the extent these systems dramatically increase the loads on the equipment.

 

If I understand this correctly a two to one system based on the 1600kg winch, factoring the 50% overload can have parts of the system stressed to 3600kg before the shear pin fails.

 

If a similar but three to one system is used part of the system can be stressed to 7200kg before the shear pin fails.

 

I know that there are other significant factors. Including stretch, friction, wheel size in pulley etc.

 

I am new to working with pulley systems and winches in the world of tree work. I suspect that a direct or redirected pull is most commonly used. If I understand this correctly, when a pull is simply redirected, for simple figures the maximum pre failure load in the system will be less than two times the failing capability of the winch. In this case 4800kg. (two times shear pin failure load)

 

So, more questions:

I can see a case for not using pulley systems with the mechanical advantage being already generated by the winch. In reality how often (if at all) are two to one and three to one systems used?

 

How do I select kit to be inline with good practice?

 

I am also interested in ensuring the right pulley selection for the cable and know very little about this. What would you good people recommend and and where can I obtain them?

 

Any other thoughts/suggestions appreciated.

 

Thanks for any help

David

[treequip]

I am in the process of understanding and selecting winching equipment. I want to ensure that the equipment I put together is all compatible and fits in with best practice guidelines. Ultimately I can see several sets of equipment being helpful given the different sizes of challenges winches can be applied to.

 

I am considering the Tirfor with a working load limit of 1600kg. I understand that this winch is designed to fail at 50% overload via a shear pin. This should mean that the pin fails at 2400kg. Is this correct?

 

As I understand it strops, shackles and pulleys are designed to fail at 400/500% overload. For example a 2000kg strop in good condition and used 'sensibly' shouldn't fail before its loaded to approximately 8000kg. Is this correct?

 

Given the redundancy (reserve strength) in the pulleys/strops and shackles etc.) is a much bigger margin is it considered acceptable/good practice to put together 'sets' of kit together based on the redundancy or not?

 

The winch obviously gives a mechanical advantage. When a more powerful pull is needed it is possible to use pulley systems. I have some concerns about the extent these systems dramatically increase the loads on the equipment.

 

If I understand this correctly a two to one system based on the 1600kg winch, factoring the 50% overload can have parts of the system stressed to 3600kg before the shear pin fails.

 

If a similar but three to one system is used part of the system can be stressed to 7200kg before the shear pin fails.

 

I know that there are other significant factors. Including stretch, friction, wheel size in pulley etc.

 

I am new to working with pulley systems and winches in the world of tree work. I suspect that a direct or redirected pull is most commonly used. If I understand this correctly, when a pull is simply redirected, for simple figures the maximum pre failure load in the system will be less than two times the failing capability of the winch. In this case 4800kg. (two times shear pin failure load)

 

So, more questions:

I can see a case for not using pulley systems with the mechanical advantage being already generated by the winch. In reality how often (if at all) are two to one and three to one systems used?

 

How do I select kit to be inline with good practice?

 

I am also interested in ensuring the right pulley selection for the cable and know very little about this. What would you good people recommend and and where can I obtain them?

 

Any other thoughts/suggestions appreciated.

 

Thanks for any help

David

 

Before we get into all that, what is it you intend to be winching?

[LeeWill]

I've got the exact same winch as u and the way I use is this... I look at my tree, get a good guess on the weight, factor in the negative lean on the tree then pull the fooker over! I used mines for dealing with road side sycamore that was all leaning to the road side, but I was able to pull them back onto the land perfectly. Where I wasn't sure if the shear pin would hold the whole tree I dismantled some of the heavier loads to reduce the pulling weight. Remember this, if ur not sure about using the winch then don't. When things go wrong it can be devastating! Negative lean on the tree (pulling it the wrong way from it's lean) adds a good few tonne to the strain of ur winch. Dismantling some of it may be time consuming, but it's worth it when the job goes perfect.

[Treewolf]

This is a complex area, and the pitfalls are many. Your post appears to contain several popular misconceptions!

 

Firstly, no device is "designed to fail at xx overload". It is designed so that it is guaranteed not to fail below xx overload.

 

Secondly, you should never under any circumstances exceed the design SWL on a piece of equipment, so the percentage overload that won't actually break it is immaterial.

 

The shear pin on a Tirfor is there to prevent the user from being able to overload the device, since there is no other way to achieve this. It is in effect the equivalent of the SLI or Overload Indicator on a crane, and if it shears the Tirfor hasn't failed, it has worked as intended!

 

A Tirfor is rated as a lifting device, and as such will have a much higher factor of safety than a pulling device. Unfortunately I don't recall the Safety Factors required by UK standards for various classifications of device, but ISTR that a winch for lifting, such as a Tirfor, has a safety factor in the region of 5 to 8.

 

The means that a Tirfor TU16, rated at 1600kg, must not fail (ie release the load) if loaded to something like 8000 to 11200 kg. This of course has nothing to do with the shear pin, which is designed to prevent you overloading the winch in the first place and can therefore fail at 1600kg.

 

A vehicle winch is not rated/tested as a lifting device and therefore has a much lower SF, in the order of 2, and this is the reason why a 4000kg vehicle winch uses SWR of a similar size to an 800kg Tirfor.

 

In any winch system the components must be selected so that none is overloaded. If you are using a 1.6T Tirfor and need a pull of up to 3.2T, you will need to achor the Tirfor to a fixed object with a shackle rated at at least 1.6T SWL, run the cable from the Tirfor round a block or snatch block rated at at least 3.2T and with as sheave (pulley) of a suitable diameter for the cable, and then anchor the cable end with another 1.6T shackle. The snatch block must be attached to the object you're pulling with a shackle etc rated to at least 3.2T.

 

The mechanics of the winching system are not necessarily complex, but you need to be aware of the max load on any compenent and rig so that no component's SWL is exceeded. Never work on the basis that because it has a SF of 2, it can be overloaded to 1.5 times its SWL.

[David Dobedoe]

Thanks all! As stated in the original post I am in the process of developing my understanding so very happy to be corrected / informed!

 

Trequip, regarding what is being winched, given I am learning about these things it will be a variety of tree work applications. Hopefully starting gently, building experience and knowledge.

 

TreeMunky, what you say makes sense and estimating weights leans etc. is not easy. When possible I fully agree with the concept 'if you think its too big make it smaller!'

And equally it may be that if i think its to big it maybe and therefore a job for somebody else!

 

Treewolf - Good stuff in your reply. So thank you again.