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winch rope or cable capacity using a snatch block
Might be dumb question but while using a snatch block to make a double line pull, it doubles your pull capacity of your winch right. So wouldn't I need to have double the capacity strength in my rope or cable? I would think so however never heard that plus I think I would have found out recently with die consequences. Running with a smittybilt xrc8 (8000 pounds) and thinking of adding synthetic line since my cable is fryed.
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No. Because each leg of the line is carrying half the pull.
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Originally Posted by grandjunktion
(Post 4080075)
Might be dumb question but while using a snatch block to make a double line pull, it doubles your pull capacity of your winch right. So wouldn't I need to have double the capacity strength in my rope or cable? I would think so however never heard that plus I think I would have found out recently with die consequences. Running with a smittybilt xrc8 (8000 pounds) and thinking of adding synthetic line since my cable is fryed.
NO - The only dumb question is the one that was never asked. NO - Don't ever use a frayed cable because sure as sh.t someone or something will get whacked really hard when it does (and it will) let go! NO - You don't have a 2:1 (double capacity) Mechanical Advantage with a single snatch block. A single sheave (wheel) block is more commonly referred to as a TURNING block used to allow pulls from different angles and is a 1:1 MA. To accomplish 2:1 MA you would need a single block attached to the load (Jeep) and a second block attached to...well...a tree or other similar anchor. Twice the amount of line is required for the hoist/pull and that is what eliminates the need for larger load capable line. also requires a larger winch drum. When you see a crane with a whole whack of lines going through multiple sheaves count the number of lines you see going between top and bottom blocks and that will tell you the Mechanical Advantage of that cranes line |
Originally Posted by Mark Doiron
(Post 4080077)
No. Because each leg of the line is carrying half the pull.
I could be wrong though...I'm just a qualified hoisting rigger. Certified by the nuclear industry. We don't allow for "oops what was that noise" |
Straight off the Warn Winch site:
"Doubling your pulling power Another type of winch rigging that uses a snatch block is the double-line pull. There are two common situations in which the double-line pull is useful. The first is if you think your winch doesn’t have enough muscle to pull out your vehicle. The second is if you want to recover a vehicle that’s bigger than yours. A double-line pull involves using the snatch block to redirect the winch cable back towards the winch. In a self-recovery situation, you’d run the cable through the snatch block and then back to your own vehicle. The snatch block is attached to an anchor point and positioned directly in front of the vehicle. If you are moving another vehicle, the stuck vehicle is attached to the snatch block. The winch cable goes through the snatch block and back to an anchor point that’s next to your vehicle. This anchor point takes some of the strain off your vehicle, which is important when you are recovering a heavier rig. This double-line setup with the snatch block doubles the pulling power of your winch. Note that when you double the power, you also cut the line speed in half." So you can use a single snatchblock to either change the angle of the pull OR double your pulling power, you don't need 2 snatchblocks for that. |
Originally Posted by rsbmg
(Post 4080097)
Straight off the Warn Winch site:
"Doubling your pulling power Another type of winch rigging that uses a snatch block is the double-line pull. There are two common situations in which the double-line pull is useful. The first is if you think your winch doesn’t have enough muscle to pull out your vehicle. The second is if you want to recover a vehicle that’s bigger than yours. A double-line pull involves using the snatch block to redirect the winch cable back towards the winch. In a self-recovery situation, you’d run the cable through the snatch block and then back to your own vehicle. The snatch block is attached to an anchor point and positioned directly in front of the vehicle. If you are moving another vehicle, the stuck vehicle is attached to the snatch block. The winch cable goes through the snatch block and back to an anchor point that’s next to your vehicle. This anchor point takes some of the strain off your vehicle, which is important when you are recovering a heavier rig. This double-line setup with the snatch block doubles the pulling power of your winch. Note that when you double the power, you also cut the line speed in half." So you can use a single snatchblock to either change the angle of the pull OR double your pulling power, you don't need 2 snatchblocks for that. Simple test on who's right here....Hyuk..Hyuk Take the biggest fish scale you can find. weigh something on it. Now hang the scale attached to the snatch block on a tree and see how much the same item weighs. |
So what size rope would be recommended for my 8000 lb capacity smittybilt winch?
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Originally Posted by 101gargoyles
(Post 4080079)
On a single sheave (wheel) both sides have equal load. I could be wrong though...I'm just a qualified hoisting rigger. Certified by the nuclear industry. We don't allow for "oops what was that noise" So we agree, right? When something is divided by two (halved), you have equal parts. His question was does he need a rope off twice the strength. |
1 Attachment(s)
Originally Posted by 101gargoyles
(Post 4080078)
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NO - You don't have a 2:1 (double capacity) Mechanical Advantage with a single snatch block. A single sheave (wheel) block is more commonly referred to as a TURNING block used to allow pulls from different angles and is a 1:1 MA. To accomplish 2:1 MA you would need a single block attached to the load (Jeep) and a second block attached to...well...a tree or other similar anchor. Twice the amount of line is required for the hoist/pull and that is what eliminates the need for larger load capable line. also requires a larger winch drum. When you see a crane with a whole whack of lines going through multiple sheaves count the number of lines you see going between top and bottom blocks and that will tell you the Mechanical Advantage of that cranes line http://4.bp.blogspot.com/-aTKiX5ED5K...EA/s1600/1.JPG https://www.jk-forum.com/forums/atta...p;d=1428068098 And OP should note that the total force (Vp) was only present on the line being pulled. Since that line is now wrapped around the winch drum, it doesn't need twice the strength. Right? Attachment 604617 My daughter is in her third year as a PhD candidate at Rice University in applied physics (she's an engineering physicist). Maybe I should just ask her? ;-) |
The last time I was winched out it took 3 winches, six snatch blocks and 3 thirty foot straps to get me back on a trail. I'd like to get a rope capable to withstand whatever force is possible for my winch with multiple snatch blocks
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