What size snatchblocks for front winch?

[rmgill]

Doesn't it depend on the way you lay the cable. In some cases, the rigging shows the final cable attached to the block which will double it's load. Shouldn't each connecting point be one equivalent part of the rig?

This load calculator has me thinking about this.
The load is divided by the number of lines pulling back and forth.

A simple redirect is double the weight on the redirecting block at a close angle.

A block moving with the load back to the winch is equal to the load, line load is now 1/2 (weight lines divided by 2)

Blocks will have their load based on how many lines run to them. If the block is used as an attachment point, for the line at the load AND as a redirect, then the load of the lines will be the load on the blocks, three lines on that block and you've got 3 parts of the load (3 lines and a 10,000 lb load and that's 10,000lbs on that block). Only two lines through a block and it's now 2/3s of the load.

So this set up, should have 5,000 lbs on the pulleys, (2 lines through @ 2500 lbs per line).

 

[rmgill]

oh, that calculator. throw in 10,000lbs as your load and see what I'm talking about with the rules of thumb.

 

[rizzo]

the math is still right no matter what the load is. all the lines add up to 10 k and all the anchor points(including the winch) on each side add up to 10 k.

 

[rizzo]

I like the rating on the warn block, but I wonder if the rating on the 5ton one that mangus and cranetruck showed us is really 5ton.

Does anyone think that the deuce winch is really a 10k winch? I think it is closer to 20k.

 

[rmgill]

I wonder if the sheave on the warn block could be swapped out.

 

[Elwenil]

Also you need to remember that while the drum is only carrying half the load, the cable gets it all as well as any mounting point that the snatch block is hooked to. There are several good books on recovery as well as a few military manuals that can help you out and keep you out of trouble.

are you talking about the winch drum? the cable and the winch only get half or whatever the winch pull is. On a 10k winch each cable leg(one going too the block and one coming from the block) get 10k. When you hook the cable coming back from the block to your truck or another anchor point that has to withstand the 10k that is on the cable.
on the other side of the snatch block you have 20k of pressure. whatever you hook the block too has to withstand 20k. on another MV I would hook two straps to each shackle and then to the block. each one of the straps have to withstand 10k each. They share the 20k load from the block. each shackle will have 10k on it instead of 20k(if you just used one shackle). Keep in mind that using a sling setup your load ratings on the straps would be reduced depending on what angle the sling is at. Since most MV's have the shackles reletily close together I don't think that this is a big factor (I use 2 11ft straps with a rating of 45k each).

I read that since the winch was the pulling part of the setup and with the varying load because of cable wraps that it carries more of the load. There was also something about the load of the rigging on the winch since it's the only "powered" part. I'm sure that would vary, but it's how I understood it. Might not be quite right, lol.

 

[Recovry4x4]

For a pretty thorough explanation on blocks and recovery DL FM 20-22 from the manual section of get the TM 5-725 (I think) on rigging. Also one needs to factor in the percentage of loss when using a block.

 

[rizzo]

[

I read that since the winch was the pulling part of the setup and with the varying load because of cable wraps that it carries more of the load. There was also something about the load of the rigging on the winch since it's the only "powered" part. I'm sure that would vary, but it's how I understood it. Might not be quite right, lol.

the winch ratings change with the number of wraps on the drum. the load on the cable is the same, but the capabilitys of the winch change with the number of wraps on the drum.

 

[cranetruck]

The big question is, how are these devices rated? How much of a safety margin is built in?
I have seen commercial snatch blocks rated over 20,000 lb that looks like toys and not to mention the commercial 4x4 electric winches with ratings similar or greater than the deuce winch rating.

 

[rmgill]

I really think it's a matter of the military gear being very conservatively rated. Look at the size of the trucks for that matter. Frames and everything else. When I was first looking at my 5 ton I showed the pictures to a co-worker that did truck repair on the side and he was oohing and ahing over the size of the frame. "that's a 5 ton?"

Bearing friction is a factor. Plain bearings vs roller bearings. The other issue is that we'll be using this gear VERY intermittently (bjorn excepted). Wear rates are going to be exceedingly low.

Wear is also an issue. That's why I said to inspect the sheaves. There's a gauge one can get for cable sizes to check the wear rate of a sheave. Take the blocks to a rigging supply company, they should be able to check and match sheaves that are out of spec I think. Any cracks or damage on the blocks and you should discard it or have it inspected by someone that knows their stuff.

But, from what I could see, you could safely get ~20,000 lbs of pull with 3 basic 5 ton blocks. Need a big re-direct because of a bad angle, then you want to get a heavier grade block.

 

[rizzo]

But, from what I could see, you could safely get ~20,000 lbs of pull with 3 basic 5 ton blocks. Need a big re-direct because of a bad angle, then you want to get a heavier grade block.

I think more smaller blocks(hopefully cheaper) would work out good. The only downfall would be that it would shorten your cable. On the other hand it would use extra cable so you can get down to the first wrap and have full pulling power. All you would need is some exstension cables or straps

 

[rizzo]

I really think it's a matter of the military gear being very conservatively rated. Look at the size of the trucks for that matter. Frames and everything else. When I was first looking at my 5 ton I showed the pictures to a co-worker that did truck repair on the side and he was oohing and ahing over the size of the frame. "that's a 5 ton?"

I was asking a guy how much they loaded on the trucks. He said they didn't payattention to weight they just loaded them till they couldn't get anymore on.

 

[rizzo]

The big question is, how are these devices rated? How much of a safety margin is built in?

yes, so how do we find out? Call the manufacturer? I have a couple blocks with data plates on them. I will check.

 

[red devils dude]

I think the military winch's are rated with only 1 wrap on the drum so there that would explain the low ratings.

 

[Elwenil]

I think all winches are rated wih one wrap. I know Warn and Ramsey are.

 

[red devils dude]

hmm that's not what there web site's said.

 

[Elwenil]

Warn example 9.5xp 9500lbs:

http://www.warn.com/truck/winches/95xp_winch.shtml

Ramsey Patriot 9500 example:

http://www.ramsey.com/winches/patriot9500.html

 

[rizzo]

I think the military winch's are rated with only 1 wrap on the drum so there that would explain the low ratings.

one wrap is the highest rating. The more wraps you get the lower the pulling power.
I clicked on the link and that is what it said for warn

Pull by layer
layer/Lbs(Kgs.)
1/9500(4313)
2/8650(4927)
3/7920 (3595)
4/7400(3359)
5/6940(3150)

 

[rizzo]

here is one of the blocks, I will try to call Johnson Wednesday.

 

[Squirt-Truck]

All winches are rated at single lay, 4 turns minimum. Limiting factor is USUALLY rope termination. The limit is generally the winch mounting method. Did not someone post a test here from Mile Marker on the winches. I believe that Ramsey was in that same test, just not published. Safety factors vary with use from 2 to one on pull winches to 6 to one for manlifting, most overhead is 4 to one. Smaller diameter blocks de-rate the rope more, almost as much as poor rope end terminations.