Fun with Numbers

[VA6489]

Many folks on the trail with me wonder why I do double line pulls for short distance recoveries. It all has to do with the rated pulling power based on how many layers or line are wrapped on the drum. Rule of thumb is for each additional layer you loose about 15% of the rated pulling power. Why? you have effectively changed the gear ratio of the winch by adding diameter to the drum. Layer 1, full rated power, second layer wraps and you now have a bigger drum due to the cable already wrapped on it. Some fun with math below.

10,000lb line pull rated winch.
Layer 1 wrapping on the bare drum yields a full rated pull of 10,000lbs. ( remember you need at least 5-7 wraps on the drum.... with this you have about 20-30 ft of line available before the next layer)
Layer 2 wrapping over layer 1 yields a 15% reduction equaling roughly 8500lbs line pull
Layer 3 wrapping back over layers 1&2 another 15% reduction equaling roughly 7225lbs line pull
Layer 4 Wrapping over all the previous layers and adding another 15% reduction in pulling power equals 6141lbs
And if the line starts to bunch up and you get a layer 5 you rated pulling power is now about 1/2 the rated line pull of the winch at 5100lbs.

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[Lost1wing]

Many folks on the trail with me wonder why I do double line pulls for short distance recoveries. It all has to do with the rated pulling power based on how many layers or line are wrapped on the drum. Rule of thumb is for each additional layer you loose about 15% of the rated pulling power. Why? you have effectively changed the gear ratio of the winch by adding diameter to the drum. Layer 1, full rated power, second layer wraps and you now have a bigger drum due to the cable already wrapped on it. Some fun with math below.

10,000lb line pull rated winch.
Layer 1 wrapping on the bare drum yields a full rated pull of 10,000lbs. ( remember you need at least 5-7 wraps on the drum.... with this you have about 20-30 ft of line available before the next layer)
Layer 2 wrapping over layer 1 yields a 15% reduction equaling roughly 8500lbs line pull
Layer 3 wrapping back over layers 1&2 another 15% reduction equaling roughly 7225lbs line pull
Layer 4 Wrapping over all the previous layers and adding another 15% reduction in pulling power equals 6141lbs
And if the line starts to bunch up and you get a layer 5 you rated pulling power is now about 1/2 the rated line pull of the winch at 5100lbs.

5100lbs is still a lot of pull. I would start with a single line pull just to save time. It would be a different story if knew I was pancaked in mud. Once you do a few recoveries, you will have a better idea of what to do.

These number are useful, but my point of starting with a 12k winch is so I don't have to get all of my gear out for a simple pull.

If someone wanted to mount a lower rated winch such as a 5k, you might have to double your line.

Good info!

 

[VA6489]

I have done more than a few recoveries over the past 45 years. A snatch block and tree saver is not a lot of gear to get out. I assume you are going to use a tree saver and at least one shackle adding a snatch block is just one more item and a double line pull is faster than a single line.
Time, unless someone is in danger (life) you have all the time in the world to develop a recover plan and execute.
Yes many times a simple lost of traction just needs a bit of pull to overcome and recover, where it get dangerous is when people are in a hurry. Flat ground is an easy pull, add a rock and a dead wheel energy needed to over come increases dramatically. Add an incline and again force increases dramatically. Yes it is easy to just rig a single line, most cases you do not pull 95 ft of line to recover, you are in many cases using half the spool thus the rated pull is much less than the 12K rated winch.

Food for thought.

 

[Blade1668]

Double line pull puts less stress on equipment and less electrical load also. Yeah my JT has a 12K but it's definitely not 12K on top wrap of line. A second on rushing in recovery leads to mistakes, possibly injuries /death and more damage.

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