Overkill? (Snatch Block)

[KevinABQ]

I like the safety factor. With no true guidelines in place for how manufacturers rate these blocks, seems logical to go with what’s worked for the past few decades.

It's also useful to absorb accidental shock loads. Don't shock load your recovery systems, it's bad. (Stealing some examples from a rigging text here) For example, a 6" drop (say off a rock) of an 8,000 pound load on 25 feet of 1/2" wire rope produces a 39,176 pound force on the wire rope. Which will almost certainly break it.

Even a tiny 1" drop produces something like 18,000 pounds of force, which you can produce by a twisted shackle untwisting under load. The worst case drop from a shackle untwisting can be about twice the length of the shackle, which will probably produce a bad day.

[TankerZak]

So first snatchblock should be 24k(ish) and 2nd snatch block should be 36k (ish).

I'm not sure I follow your logic on this. Maybe a diagram would make it a little clearer.

This is with jeep weights but you can see all the math. So where it says 9k change it to 12k and then multiply out. That 18k becomes 24k and the 27k becomes 36k.

[Low_Sky]

So first snatchblock should be 24k(ish) and 2nd snatch block should be 36k (ish).

I'm not sure I follow your logic on this. Maybe a diagram would make it a little clearer.

This is with jeep weights but you can see all the math. So where it says 9k change it to 12k and then multiply out. That 18k becomes 24k and the 27k becomes 36k.

Screenshot_20180209-165618.jpg

Yeah, that’s wrong. Both blocks in that triple line pull see 18k lbs.

[MJockey]

That's one heavy jeep.

[TankerZak]

I'm not sure I follow your logic on this. Maybe a diagram would make it a little clearer.

This is with jeep weights but you can see all the math. So where it says 9k change it to 12k and then multiply out. That 18k becomes 24k and the 27k becomes 36k.

Screenshot_20180209-165618.jpg

Yeah, that’s wrong. Both blocks in that triple line pull see 18k lbs.

Could be wrong. I didn't do the math and frankly have forgotten how since my physics and engineering class days, lol.

[TankerZak]

I'm not sure I follow your logic on this. Maybe a diagram would make it a little clearer.

This is with jeep weights but you can see all the math. So where it says 9k change it to 12k and then multiply out. That 18k becomes 24k and the 27k becomes 36k.

Screenshot_20180209-165618.jpg

Yeah, that’s wrong. Both blocks in that triple line pull see 18k lbs.

Could be wrong. I didn't do the math and frankly have forgotten how since my physics and engineering class days, lol.

[TankerZak]

I'm not sure I follow your logic on this. Maybe a diagram would make it a little clearer.

This is with jeep weights but you can see all the math. So where it says 9k change it to 12k and then multiply out. That 18k becomes 24k and the 27k becomes 36k.

Screenshot_20180209-165618.jpg

Yeah, that’s wrong. Both blocks in that triple line pull see 18k lbs.

Could be wrong. I didn't do the math and frankly have forgotten how since my physics and engineering class days, lol.

[TankerZak]

I'm not sure I follow your logic on this. Maybe a diagram would make it a little clearer.

This is with jeep weights but you can see all the math. So where it says 9k change it to 12k and then multiply out. That 18k becomes 24k and the 27k becomes 36k.

Screenshot_20180209-165618.jpg

Yeah, that’s wrong. Both blocks in that triple line pull see 18k lbs.

Could be wrong. I didn't do the math and frankly have forgotten how since my physics and engineering class days, lol.

[TankerZak]

That's one heavy jeep.

It's not the weight of the jeep. Its the pull power of the winch. If you have a 4000lb jeep its stuck factor varies and increases the force needed to pull it. Gravity, angles, hills, terrain, what your actually stock on or in (mud, sand, snow, etc.). What won't change is how hard your winch can pull at max. Beyond that you have to add mechanical advantage to increase what your winch can do. You just have to know where the forces are being applied. And rule of thumb I've seen for winches is they should be between 1.5 and 2x the weight of the vehicle they are mounted on.

[TankerZak]

That's one heavy jeep.

It's not the weight of the jeep. Its the pull power of the winch. If you have a 4000lb jeep its stuck factor varies and increases the force needed to pull it. Gravity, angles, hills, terrain, what your actually stuck on or in (mud, sand, snow, etc.). What won't change is how hard your winch can pull at max. Beyond that you have to add mechanical advantage to increase what your winch can do. You just have to know where the forces are being applied so you don't over work your weakest piece. And rule of thumb I've seen for winches is they should be between 1.5 and 2x the weight of the vehicle they are mounted on.

[Low_Sky]

This is with jeep weights but you can see all the math. So where it says 9k change it to 12k and then multiply out. That 18k becomes 24k and the 27k becomes 36k.

Screenshot_20180209-165618.jpg

Yeah, that’s wrong. Both blocks in that triple line pull see 18k lbs.

Could be wrong. I didn't do the math and frankly have forgotten how since my physics and engineering class days, lol.

Could be definitely wrong. If you neglect drag at the blocks, the winch line carries the same tension throughout during the pull. If you’re assuming the winch is at max pull (9k lbs), a block with a zero degree line angle is seeing double that (18k lbs). You’d have to rig a compound advantage to see more than double the winch rating on a single block (double line pull into another double line pull).

I’m working on a rigging calculation guide for all the nerds, with PW-specific examples. Gonna post it in a new thread and drop a link in my build thread so I don’t loose it. Should be done in a day or two.

[TankerZak]

Yeah, that’s wrong. Both blocks in that triple line pull see 18k lbs.

Could be wrong. I didn't do the math and frankly have forgotten how since my physics and engineering class days, lol.

Could be definitely wrong. If you neglect drag at the blocks, the winch line carries the same tension throughout during the pull. If you’re assuming the winch is at max pull (9k lbs), a block with a zero degree line angle is seeing double that (18k lbs). You’d have to rig a compound advantage to see more than double the winch rating on a single block (double line pull into another double line pull).

I’m working on a rigging calculation guide for all the nerds, with PW-specific examples. Gonna post it in a new thread and drop a link in my build thread so I don’t loose it. Should be done in a day or two.

That'd be awesome. I don't want to do the math i just want to track the basics so I don't go over a limit. Like I have no interest in the drag difference between steel and synthetic line across a variety of snatch blocks based on materials used. But knowing the major forces on different worst case scenarios would be nice...

[Vee]

Use the app on this:
https://www.safe-xtract.com
This is the app that our recovery trainer uses for Colorado 4x4 Rescue and recovery .

[Vee]

Use the app on this:
https://www.safe-xtract.com
This is the app that our recovery trainer uses for Colorado 4x4 Rescue and recovery .

[MJockey]

Use the app on this:
https://www.safe-xtract.com
This is the app that our recovery trainer uses for Colorado 4x4 Rescue and recovery .

Do they make a recovery kit for the PW? Their web site doesn't have a whole lot of info.