Line Breaking Strength

[Jeremy Cobb]

I have a 12k Winch with 3/8 x 80' synthetic line that has a breaking strength of 17,200 pounds. I have some of the bigger soft shackles also from Bubba Rope that are 7/16 and have a 52,000 pound breaking strength. My tree hugger is 58,000 pound strength.

It's my understanding that if setup a double pull with my winch that roughly doubles the strength of my winch to 24k pulling power. That will mean that my pulley, or snatch block needs to have a breaking strength of at least 24k to handle a double pull. But what about the winch line, would that mean it also has to have 24k, or does it stay at 12k? I would assume it doesn't double like the pulley, because I don't know of any winch line that has breaking strength capable of handling 24k+ pounds.

 

[Road]

The line strength doubles by the fact that there will be two lengths and no longer a single line.

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[Jeremy Cobb]

The line strength doubles by the fact that there will be two lengths and no longer a single line.

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By that do you mean that a 17k line is suddenly capable of 34k?

 

[Road]

By that do you mean that a 17k line is suddenly capable of 34k?

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No.
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[Jeremy Cobb]

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No.
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Then how do people do a double pull with a snatch block and their line not break? Because most lines have between a 14-17k strength. And most people are running at least a 10k winch (doubling that makes 20k).

 

[slomatt]

In a double line pull each section of rope carries 1/2 of the load applied to the snatch block. So, if your winch is pulling 10k then the force on each "side" of the rope is 10k and the force on the snatchblock is 20k.

There's a picture on this site.

Snatch blocks

I have an 8000lb winch and am looking at snatch blocks. Is a 1200# strong enough or should I go bigger? If I am doing the math right then when adding a snatch block I double my max load right? So should I double what my winch can pull so I don't make an impromptu rocket? Sent from my...

risingsun4x4club.org

If you have a 12k winch then in theory the most force it could exert on a snatchblock (and shackle and tree saver) would be 2x12k = 24k. You could use this as your WLL (working load limit) for the hardware, and if you then apply a 3:1 safety factor you would want hardware with a 3x24k = 72k MBS (minimum breaking strength). You'll notice that the MBS for most common snatch blocks is nowhere near this high.

- Matt

 

[Charles M]

The following is a good example of basic loads. Each pulley you put in the system will increas your pulling power without putting more load on the winch.

 

[Road]

Then how do people do a double pull with a snatch block and their line not break? Because most lines have between a 14-17k strength. And most people are running at least a 10k winch (doubling that makes 20k).

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Look at and try to understand the other answers here, too.

The material itself does not "suddenly" become twice as strong. The pulling power becomes twice as strong because you are doubling the line with a pulley or snatch block. The load is spread across two lines, not one. The breaking point is still the same at any point in the line, but because you are doubling the line, the total pull weight is half on each part of the line.

If you set up two pulleys with the same load you decrease the load on each run of line further.

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