5/16" Viking winchline strength

[RSB]

I apologize in advance if this question has already been answered in another thread. I still haven't found the answer I'm looking for despite all my searching. I've probably just been over-thinking it. Any feedback would be appreciated...

I'm trying to understand how a 5/16" Viking winchline is strong enough to use with a snatch block connected to a winch with 8,000 lbs of pulling capacity. For example, 8,000 lbs of pulling capacity will place a 16,000 lb load on a snatch block at a factor of 2 (0 degrees). This also places a 16,000 lb load on the shackle.

If this is correct, the winchline would need to support at least 16,000 lbs. The rating however, is for only 12,300 lbs and would therefore not be sufficient to use with a snatch block going straight back to the truck (factor of 2 pulling capacity). Surely this can't be correct.

I think I might need some clarification....

thanks in advance!

 

[RU55ELL]

The force on the winchline is cut in half when you use a snatchblock at 0*.

 

[RSB]

so, 8,000 lbs BEFORE the snatch block and 8,000 lbs AFTER the snatch block (which would mean 8,000 lbs on the shackle connected to the truck after the snatch block)?

...which would also mean 16,000 lbs on the snatch block itself?

 

[RU55ELL]

Correct.

 

[RSB]

Correct.

ok, I think I've been confusing force with pulling capacity then. They're two different things? Just didn't makes sense to me how 8,000 lbs (force applied to the bow shackle connected to the truck AFTER the snatch block) could pull 16,000 pounds. But it does... right?

 

[RSB]

perhaps force and pulling capacity are the same thing? Because two parts of the rope are pulling now? 8,000 lbs (BEFORE the snatch block) + 8,000 lbs (AFTER the snatch block) = 16,000 lbs?

 

[JPK]

perhaps force and pulling capacity are the same thing? Because two parts of the rope are pulling now? 8,000 lbs (BEFORE the snatch block) + 8,000 lbs (AFTER the snatch block) = 16,000 lbs?

This one has got it.

Look again at Russell's diagram. His picture is worth any amount of written explanation.

F = Pulling force. F is divided by two when you use a snatch block (assuming 0* and no friction) So the winch sees 1/2 of F and the clevis 1/2. The snatch block connection to the tree, winched vehicle or whatever is F.

Keep in mind that the total force on the winching vehicle is F also, and so it is frequently required to anchor the winching vehicle when using a snatch block to winch out a stuck vehicle or move something heavy or creating a lot of drag...

Alternatively, if the winching vehicle is the one stuck, the anchor for the snatch block needs to be able to withstand 2x the rated capacity of the winch or F, whichever is higher. Since F is unknown, safest to do your best to ensure that the anchor is up to 2x winch rating. (A good reason for winch ropes as opposed to wire.)

BTW, I have always used winch ropes rated 2x the winch rating or more, thinking that with friction, fraying, real world situations there must be a point or section of line which sees more than 1/2 of F.

JPK

 

[timmer2008]

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rigging training at industry rates. books charts DVDs and other cool stuff.

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[RSB]

thank-you JPK! What confuses me is being told differently by someplace else. What you're saying is the same thing I was thinking!

here was the question...

...when double rigging, I think I figured it out. For example, 8,000 lbs of pulling capacity places a 16,000 lb load on the snatch block (factor of 2), but there's still only 8,000 lbs on the shackle, since the load on the line is halved at the snatch block. This essentially means two 8,000 lb lines are pulling the truck, therefore providing 16,000 lb of total pulling capacity.

Is this correct?"

answer...

Regarding your snatch block question, you would have 16000 lbs on the shackle if attached to the block. Just imagine putting an inline scale on what you are attaching to (whether it be a shackle, tree, single line, etc)……you would still measure 16000 lbs. There are not two lines pulling the truck, just one long one that gets its speed cut in half (by the snatch block) but with double the power at the attachment point of the snatch block.

contemplating this answer, I thought... ok, if there aren't two lines supporting the load, then there's only one. Doubling the power means at some point, the line can pull 16,000 pounds, which therefore places 16,000 lbs on the bow shackle—thus my concern about the strength of the winchline.

I like your answer better, it makes more sense. But which is right?!

This one has got it.

Look again at Russell's diagram. His picture is worth any amount of written explanation.

F = Pulling force. F is divided by two when you use a snatch block (assuming 0* and no friction) So the winch sees 1/2 of F and the clevis 1/2. The snatch block connection to the tree, winched vehicle or whatever is F.

Keep in mind that the total force on the winching vehicle is F also, and so it is frequently required to anchor the winching vehicle when using a snatch block to winch out a stuck vehicle or move something heavy or creating a lot of drag...

Alternatively, if the winching vehicle is the one stuck, the anchor for the snatch block needs to be able to withstand 2x the rated capacity of the winch or F, whichever is higher. Since F is unknown, safest to do your best to ensure that the anchor is up to 2x winch rating. (A good reason for winch ropes as opposed to wire.)

BTW, I have always used winch ropes rated 2x the winch rating or more, thinking that with friction, fraying, real world situations there must be a point or section of line which sees more than 1/2 of F.

JPK

 

[RSB]

thank-you. I'm definitely interested in purchasing some of this material. I also plan on taking some classes on these techniques through Overland Journal. I'm just having difficulty understanding some of the basics and getting them straightened out in my head!

all you every wanted to know about rigging and then some

http://www.thecrosbygroup.com/default.aspx?tabid=54

rigging training at industry rates. books charts DVDs and other cool stuff.

http://www.thecrosbygroup.com/default.aspx?tabid=71

 

[JPK]

I believe both are correct regarding F applied to the clevis, but because each answer contemplates the clevis/shackle at different locations.

Look again at Ru55ell's diagram.

My answer contemplates having "the" clevis at the winching vehicle, connecting the end of line hook to the winching vehicle. The other end of the winch line is also on the winching vehicle, at the winch drum. If you were to place a scale at the clevis and drum, each would pull the scale to 1/2 of the force being applied to the snatch block.

(And this is why we carry snatch blocks, they multiply the rating of the winch. The winch doesn't change, it can still only pull X pounds. And the line speed at rated winch capacity doesn't change. Overall advance is halved - at 0* - because of the snatch block - the force multiplier.)

I believe the answer you quoted contemplates "the" clevis at the snatch block, as one would be if used to attach the snatch block to a stuck vehicle or to a strap around a tree, etc. There, the scale would be pulled down the full F, or up to twice the winch rating.

One reason that I use a winchline rated at least 2x the winch rating is that I recall somewhere some time ago I reading an article or something and reviewing a table that showed the F applied to the line around the snatchblock, and iirc, the pull the line has to endure around the snatch block is much greater than 1/2 F.

Interestingly, more recently I saw a table that gave a multipleir of F for different angles off of a pivot for static weight - it was used for picture hanging of all things. Suffice to say that the force applied to the winch drum and the clevis used to attach the end of line hook grow as the distance/angle between them grows if F at the snatch block were to remain constant. But the F applied to the snatch block drops as the angle between drum and ancor increases since total F is no longer 2 x winch capacity.

Hope this helps,

JPK

 

[Stumpalump]

5/16 is thin for a vehicle winch line because syntheic abraids and cuts easy. The first small nick in it leaves it scary thin and it's not if you nick it's when and how bad you let it get before you replace it. Go thick and carry an extra strap for an extension.

 

[RSB]

JPK, this clarifies everything entirely. Thank-you so, so much your thorough response. I think this is exactly what happened. The answer I quoted was referring to the clevis on the block, not the truck itself (in that situation)—which COMPLETELY threw me off.

so, from what I'm understanding then—because I have a winch capable of 8,000 lbs pulling capacity (at its peak), the force on the line shouldn't exceed 8,000 lbs, with exception to around the snatchblock—which is why you recommend a winchline rated at at least 2x the winch pulling capacity.

a 5/16 line isn't the most ideal then, but still well below the minimum 16,000 lbs I initially thought it would need to be rated for using a snatch block at a factor of 2 with a winch rated of 8,000 lbs of pulling capacity.

again, much appreciated. Now that I have a much better understanding I can start practicing using the equipment!

I believe both are correct regarding F applied to the clevis, but because each answer contemplates the clevis/shackle at different locations.

Look again at Ru55ell's diagram.

My answer contemplates having "the" clevis at the winching vehicle, connecting the end of line hook to the winching vehicle. The other end of the winch line is also on the winching vehicle, at the winch drum. If you were to place a scale at the clevis and drum, each would pull the scale to 1/2 of the force being applied to the snatch block.

(And this is why we carry snatch blocks, they multiply the rating of the winch. The winch doesn't change, it can still only pull X pounds. And the line speed at rated winch capacity doesn't change. Overall advance is halved - at 0* - because of the snatch block - the force multiplier.)

I believe the answer you quoted contemplates "the" clevis at the snatch block, as one would be if used to attach the snatch block to a stuck vehicle or to a strap around a tree, etc. There, the scale would be pulled down the full F, or up to twice the winch rating.

One reason that I use a winchline rated at least 2x the winch rating is that I recall somewhere some time ago I reading an article or something and reviewing a table that showed the F applied to the line around the snatchblock, and iirc, the pull the line has to endure around the snatch block is much greater than 1/2 F.

Interestingly, more recently I saw a table that gave a multipleir of F for different angles off of a pivot for static weight - it was used for picture hanging of all things. Suffice to say that the force applied to the winch drum and the clevis used to attach the end of line hook grow as the distance/angle between them grows if F at the snatch block were to remain constant. But the F applied to the snatch block drops as the angle between drum and ancor increases since total F is no longer 2 x winch capacity.

Hope this helps,

JPK

 

[RSB]

agreed. In addition to the 2x safety margin I'd get to account for the line around the block, the additional braids would be nice to have for more protection. My next line will be a 3/8!

my primary concern about the load, however, has been answered and for now—at least I know the line I already have is capable of doing the job. :sombrero:

5/16 is thin for a vehicle winch line because syntheic abraids and cuts easy. The first small nick in it leaves it scary thin and it's not if you nick it's when and how bad you let it get before you replace it. Go thick and carry an extra strap for an extension.