If using a snatch block and doubling the line, doesn't it equate doubling the power of your winch?
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Yep a pulley effectively doubles the capacity but it cuts the winching speed in half.
CharlieS
GOLD Star
Sometimes, but it depends. Smarter people than me should weigh in, since there is math involved and that's never been my strong suit. As I understand it, a snatch block can be a force multiplier or just a way to redirect. I think a basic double line pull from the winching vehicle to a fixed anchor point with a snatch block and back to the winching vehicle will give you that 2:1 multiplier. Then again, if you are winching from a stuck vehicle, to a snatch block on a fixed anchor point and then running it another fixed anchor, you are doing a redirect (and not getting the 2:1 force multiplier). There's a whole other forum on mud for this if you want good info from experts - people that have done this forever or are professional riggers.
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Not quite sure that I agree. If you put a snatch block on a tree and the line goes from the truck, through the block and attaches to the truck I don’t think there is any mechanical advantage. I think that you would have to have two blocks and go from truck to tree to truck and back to tree to gain a mechanical advantage. It’s no different than a pulley on a branch lifting a pail.
This is correct.
Winch -> pulley -> back to winching vehicle = 2:1 advantage.
Winch -> pulley -> not back to winching vehicle = 1:1, no advantage.
What is a Snatch Block? how to use a pulley with a winch - Garatools.com
As an affiliate for Amazon and other retailers I earn from qualifying purchases. Learning how to use a snatch block, also know as a pulley block, is an essential vehicle recovery skill for off-roading and overlanding. A snatch block is a heavy-duty pulley inside a metal casing that is used with...
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All good food for thought. I thought I was being generous with opting for the 10k over the 8k. I'm usually pretty light in overlanding mode, probably 6600 lbs. Only way I'm at that weight is by pinching pounds everywhere I can. Which is part of the why for the steel cable VR EVO. The VR EVO 10S includes a steel fairlead and steel hook. Would like aluminum for the fairlead, partly for long term rust avoidance. And maybe even forego a hook as @CharlieS has done. Just need to bring my own synthetic line. Incrementally lighter and cheaper than the delivered 10S solution.
Not set on anything so still noodling.
Thinking out here in the arid desert, probably best to keep full length line in hopes that it can actually reach something.
Not set on anything so still noodling.
Thinking out here in the arid desert, probably best to keep full length line in hopes that it can actually reach something.
CharlieS
GOLD Star
Pulling a rope through a pulley on a branch to a pail is a 1:1 (redirect), with no mechanical advantage.
The 2:1 pull would be if the rope went back to a winch on the pail. That is the direct equivalent to the winch on winch truck to snatch block on anchor to winch truck.
winch to tree (anchor), no snatch block - roughly 1:1 ( single line pull)
winch truck to snatch block on tree (anchor) and back to truck - roughly 2:1 (double line pull)
winch truck to to snatch block on tree (anchor), back to snatch block on winch truck, and back to tree (anchor) - roughly 3:1 (triple line pull)
Roughly because there are frictional losses
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CharlieS
GOLD Star
@TeCKis300 if you grab a factor55 fast fid, some whipping twine with needle, and learn how to use them (easy enough) you can make custom winch lines, bridles, winch line extensions, and the like so much cheaper than buying them. The fast fid is great for field repairs too (line splice, re-terminate a snapped line). And in line with your build, they're light.
You don't have to agree, but the laws of physics say I'm right (for once!)
It's a 2:1 benefit if you've attached the winch hook back to your truck, or 1:1 if you've attached the hook at the end of your winch line to something else.
Double-Pull
One of the best pieces of equipment you can carry with you on a romp into the backcountry is a snatch block that accompanies your winch.
www.treadmagazine.com
"Thanks to mechanical advantage of a pulley doubling back to its origin, you can effectively double the pulling power of your winch at a cost of half the speed of recovery. You do this by placing the snatch-block at the anchor point, and looping the winch line through the pulley and back to an anchor point on the vehicle itself."
In the "normal" way we think of the benefits of a pulley you'd be correct @GordJ. If you're using a pulley to move another object (like another truck) then one pulley attached to a tree only changes the direction of the pull, not the effort required. You're only getting the benefit of one side of the pulley, effectively. However winching back to yourself means you get the benefit of the force applied to both sides of the pulley, not just one side.
The classical physics comparison is that the pulley is attached to a movable object and winch line is fixed and thus as you pull the pulley (and attached object) gets closer. That's not actually what's happening here, but the resulting physics force is the same.
Heh. You with eight pulleys and enough rope you could winch an empty 737, assuming you're willing to wait that long...
One day I’ll be a big boy and do stuff like this. A multi vehicle pulley rescue would be cool as f to see.
When I get a new bumper, I have been warned so many times about dismemberment and grave injuries that I have no idea which route to go on cables, hooks or anything else. Better to always get higher rated stuff I guess?
No. Well, really it depends.
If $ is no object it's better to get a winch with more pulling power. There's more to a winch than just the weight rating - you have to consider duty cycle, pulling speed, etc. Realistically you're trading off $ for winch capacity though, and you might be better off investing some of those $ into other gear or mods.
For other gear you want stuff that is properly rated for the working load and that has a sufficient breaking strength. That said if you're trying to pull a 737 (or just get yourself out of a really sticky mud hole) you need to consider where you want your failure point to be. Consider:
- If your shackles or snatch blocks are the weak point and they break you could have hunks of steel flying around
- If your winch line, kinetic recovery straps, tree saver, etc are the weak link they could go flying as well. Having something to dampen and absorb the energy (like a blanket tied to the winch line) helps here, but even still things can go sideways quickly
- As discussed in a recent thread some equipment like kinetic ropes are designed to stretch and then release their energy to help in the recovery. Too little rating and they will break; too much rating and they won't stretch
- If everything you buy has a 1,000,000# load rating and will never break, when you try to pull that 737 (or your buddy stuck on a rock) the weak point is going to be your vehicle frame (or the bumper mounts).
Disclaimer: I'm not a winching expert. I've watched a bunch of videos and I've done a couple recoveries. There's a subsection of the forum with people far more experienced than I am.
We were taught that each wheel reduces mechanical advantage by 10% because of friction. Obviously a general rule of thumb but there is still loss of efficiency.
CharlieS
GOLD Star
That'd be some pain in the neck math for someone like me - you can't say 10 pulleys each reduces by 10% so it reduces by 100%. It must be "of the load applied to that pullley", so some goofy math I forgot or never learned how to do. I don't think it probably matters all that much in the kind of vehicle winching we do, at least for practical purposes. Stuff like number of stuck wheels, angle of incline, whether it is assisted or non-assisted, probably matter a lot more, and most also have some good rules of thumb for use in the field.
I really like @linuxgod s reminders about keeping in mind the forces involved and weak links. If you are winching from a vehicle and hooking back to that vehicle for a multi-line pull, you are potentially adding a huge force multiplier and the winching vehicle is feeling all of that force. I try to keep this in mind - flying winch lines, bumper parts and tackle are bad bad bad.
I really like @linuxgod s reminders about keeping in mind the forces involved and weak links. If you are winching from a vehicle and hooking back to that vehicle for a multi-line pull, you are potentially adding a huge force multiplier and the winching vehicle is feeling all of that force. I try to keep this in mind - flying winch lines, bumper parts and tackle are bad bad bad.
The math is easy, I just googled "pulley force calculator". First link:
At 100% efficiency:
At 90% efficiency:
I'm not sure the impact on winching speed with 8 or 9 pulleys but I presume patience isn't just a virtue in that case, it would be a necessity.
Thanks for that breakdown. This is exactly why I'm in serious analysis paralysis with some mods.
I haven't gotten as far as recovery planning yet, im still looking at under the skin options for "fixing" my truck from factory or mod induced shortcomings but each and every decision has so much nuance and know how involved that its some serious research to satisfy my level of satisfaction to pull a trigger.
It seems like the truck will finally be done in 20 years when i will finally be able to justify tossing it around and scratching it all up LOL.
But for someone like me, the journey is most of the fun anyway
. Ill surely be sad when its all done.Lol.. It was a ”rule of thumb” because size of wheel, quality of bearings etc. come into play and we never used more than 6 part blocks before we moved to come alongs and chain hoists.9 pulleys then? Or 8 pulleys and a massive tube of graphite?
