Winch Rigging and Anchor loads

[Rob]

OK, I think I have the principle I was looking for in scenario three above from that link I sent:

Situation 3: 
Load:  8,000 lbs
# of snatch blocks:  2
Total load 8,000+1600 = 9600
Load per line:  9,600/3=3,200

Load on Winch:  3,200 lbs
Load on Anchor 1:  6,400 lbs
Load on Anchor 3:  6,400 lbs
Load on Anchor 1:  3,200 lbs

What's the additional 1600# from?

Tackle resistance. 

From that link:
18. Tackle Resistance
Due to friction created by a sheave rotating on its
pin, flexing of the rope around the sheave, and
the rope scuffing in the groove of the sheave, there
is a loss in energy as the rope passes around the
sheave. This loss is considered as resistance because it must be overcome before the resistance
of the load can be overcome. Each sheave in the
rigging will create resistance. The rule to determine tackle resistance is: 10 percent of the load
resistance times the number of sheaves (not
blocks) in the rigging. As an example, a load resistance of 30,000 pounds and a tackle with 3
sheaves is being used, 10 percent of 30,000 pounds
equals 3,000 pounds, times 3 (3 sheaves) equals
9,000 pounds tackle resistance

[Rob]

Short answer is, count the # of snatch blocks, and add 10 of load for each one.

Two snatch blocks on an 8K lb load = +20%, or 1,600 lbs.

[hunter399]

OK, I think I have the principle I was looking for in scenario three above from that link I sent:

Situation 3: 
Load:  8,000 lbs
# of snatch blocks:  2
Total load 8,000+1600 = 9600
Load per line:  9,600/3=3,200

Load on Winch:  3,200 lbs
Load on Anchor 1:  6,400 lbs
Load on Anchor 3:  6,400 lbs
Load on Anchor 1:  3,200 lbs

What's the additional 1600# from?

Tackle resistance. 

From that link:
18. Tackle Resistance
Due to friction created by a sheave rotating on its
pin, flexing of the rope around the sheave, and
the rope scuffing in the groove of the sheave, there
is a loss in energy as the rope passes around the
sheave. This loss is considered as resistance because it must be overcome before the resistance
of the load can be overcome. Each sheave in the
rigging will create resistance. The rule to determine tackle resistance is: 10 percent of the load
resistance times the number of sheaves (not
blocks) in the rigging. As an example, a load resistance of 30,000 pounds and a tackle with 3
sheaves is being used, 10 percent of 30,000 pounds
equals 3,000 pounds, times 3 (3 sheaves) equals
9,000 pounds tackle resistance

This sounds about right to me.👍

[Rob]

So circling back to my original set of questions:

Variables:
Load 4 Tons (8,000 lbs)
Tackle resistance (10% of load per snatch block sheave)
Max Winch pull (6 tons, 12,000 lbs)
Pull per line = total load with resistance / # of lines
Load per anchor = load per line * # of lines to anchor

Situation 1:  Single Line:
Mechanical Advantage = 1:1
Load on Winch:  8,000 lbs
Load on Anchor:  8,000 lbs

Situation 2:
Mechanical Advantage = 2:1
load:  8,000 lbs
# of snatch blocks:  1
Total load:  8,800 lbs
Load per line:  4,400 lbs
Load on the Anchor:  8,800 lbs
Load on the winch:  4,400
Load on the truck anchor shackle:  4,400
Total load on the truck itself across all anchor points:  8,800


Situation 3: 
Load:  8,000 lbs
# of snatch blocks:  2
Total load 8,000+1600 = 9600
Load per line:  9,600/3=3,200

Load on Winch:  3,200 lbs
Load on Anchor 1:  6,400 lbs
Load on Anchor 2:  3,200 lbs
Load on Anchor 3:  6,400 lbs
Total load on vehicle (3,200+6,400)=9,600

Consequently, if you move anchors 1 and 2 to the same tree, the tree will see 9,600 lbs of pull with 3,200 of the pull being felt by Anchor 2 and 6,400 being felt by anchor 1.

So if you have a weak link in anchor material, put it on anchor 2….

[Rob]

And if you are looking for a 3x margin for anchor materials, then in the situations above, approx. 30K would give you that.  (Still not clear if you want 30K in WLL or MBL)

however, if you are dealing with a slope or mire situation, then the load penalties add up fast...

Grade resistance:  max resistance is the weight of the load
Overturning resistance:  should be estimated as = to 1/2 of the vehicle weight
Mire resistance:
   • Wheel depth = 1x load
   • Fender depth 2x load
   • Cab depth 3X load


Taking into consideration that pulling an 8K lb vehicle across flat, smooth ground will only require about 800 lbs of pull.  So honestly, if a truck weighs in at 8K, and is mired in mud to the wheels, then the numbers of my 3 scenarios above would work out.  otherwise, I would be way over winched (which is good news). 

If mired to the fenders, then 8K becomes 16K plus tackle resistance, so I would have to use a 2:1 or 3:1 system and consider the loads being put on anchors and anchor gear very carefully.

[Rob]

Situation 3 with max winch pull of 12,000 lbs (load would need to be 10K lbs with tackle resistance of 20% (10,000*1.2 = 12,000)
Each line would be pulling 12K (6 Tons)
This would put:
   • 24K on anchor 1
   • 12K on anchor 2
   • 24K on anchor 3
   • Total pull on the truck would be 36K!  That could very easily pull a bumper off, or destroy a winch mount.
A suppose a way to throttle the power of the winch is to leave layers of line on the spool. 
Layer 1:  12,000 (100%)
Layer 2:  9,517 (79%) (approx. full weight of truck is 8,500)
Layer 3:  7,885 (66%)
Layer 4:  6,732 (56%)

Leaving 3 full layers on the spool and starting your winching on the 4th layer would reduce the 36,000 pull down to around 20,200 lbs.  If that is spread with the winch mount taking 6732 lbs and a frame mounted tow hook taking 13,464 lbs that would help reduce risk if you are worried a deeply mired extraction might exceed working capacities of your rigging.

[ghosthunter]

Careful out there


https://www.bing.com/videos/search?&q=removing+stumps+with+block+and+tackle&view=detail&mid=16D367DA5FA1404476DD16D367DA5FA1404476DD&form=VDMCNR&ajaxhist=0&rvsmid=614AA48F75A260B37A12614AA48F75A260B37A12

[ghosthunter]

https://www.bing.com/videos/search?&q=pulling+stumps+with+snatch+blocks&docid=608050245879618448&mid=C4729FA4A65E46B2432BC4729FA4A65E46B2432B&view=detail&form=VDMCNR&rvsmid=529A6A72DA0D50D429C5529A6A72DA0D50D429C5&ajaxhist=0

[KFhunter]

So circling back to my original set of questions:

Variables:
Load 4 Tons (8,000 lbs)
Tackle resistance (10% of load per snatch block sheave)
Max Winch pull (6 tons, 12,000 lbs)
Pull per line = total load with resistance / # of lines
Load per anchor = load per line * # of lines to anchor

Situation 1:  Single Line:
Mechanical Advantage = 1:1
Load on Winch:  8,000 lbs
Load on Anchor:  8,000 lbs

Situation 2:
Mechanical Advantage = 2:1
load:  8,000 lbs
# of snatch blocks:  1
Total load:  8,800 lbs
Load per line:  4,400 lbs
Load on the Anchor:  8,800 lbs
Load on the winch:  4,400
Load on the truck anchor shackle:  4,400
Total load on the truck itself across all anchor points:  8,800


Situation 3: 
Load:  8,000 lbs
# of snatch blocks:  2
Total load 8,000+1600 = 9600
Load per line:  9,600/3=3,200

Load on Winch:  3,200 lbs
Load on Anchor 1:  6,400 lbs
Load on Anchor 2:  3,200 lbs
Load on Anchor 3:  6,400 lbs
Total load on vehicle (3,200+6,400)=9,600

Consequently, if you move anchors 1 and 2 to the same tree, the tree will see 9,600 lbs of pull with 3,200 of the pull being felt by Anchor 2 and 6,400 being felt by anchor 1.

So if you have a weak link in anchor material, put it on anchor 2….

There's only 1 line though, and its still 8000lbs,  -10% after each block. 

Don't go by what you think the load is, but total rated capacity.  The load will be highly variable.  I wouldn't even include the load in your equations, it'll either pull, or it won't.   


When winching you only add blocks if the last method failed.

Direct pull = fail
Add block, did it pull?

Dig     

I don't really see a whole lot of situations going more than one block, you'll run out of line and gear quickly.

[Ridgeratt]

So circling back to my original set of questions:

Variables:
Load 4 Tons (8,000 lbs)
Tackle resistance (10% of load per snatch block sheave)
Max Winch pull (6 tons, 12,000 lbs)
Pull per line = total load with resistance / # of lines
Load per anchor = load per line * # of lines to anchor

Situation 1:  Single Line:
Mechanical Advantage = 1:1
Load on Winch:  8,000 lbs
Load on Anchor:  8,000 lbs

Situation 2:
Mechanical Advantage = 2:1
load:  8,000 lbs
# of snatch blocks:  1
Total load:  8,800 lbs
Load per line:  4,400 lbs
Load on the Anchor:  8,800 lbs
Load on the winch:  4,400
Load on the truck anchor shackle:  4,400
Total load on the truck itself across all anchor points:  8,800


Situation 3: 
Load:  8,000 lbs
# of snatch blocks:  2
Total load 8,000+1600 = 9600
Load per line:  9,600/3=3,200

Load on Winch:  3,200 lbs
Load on Anchor 1:  6,400 lbs
Load on Anchor 2:  3,200 lbs
Load on Anchor 3:  6,400 lbs
Total load on vehicle (3,200+6,400)=9,600

Consequently, if you move anchors 1 and 2 to the same tree, the tree will see 9,600 lbs of pull with 3,200 of the pull being felt by Anchor 2 and 6,400 being felt by anchor 1.

So if you have a weak link in anchor material, put it on anchor 2….

There's only 1 line though, and its still 8000lbs,  -10% after each block. 

Don't go by what you think the load is, but total rated capacity.  The load will be highly variable.  I wouldn't even include the load in your equations, it'll either pull, or it won't.   


When winching you only add blocks if the last method failed.

Direct pull = fail
Add block, did it pull?

Dig     

I don't really see a whole lot of situations going more than one block, you'll run out of line and gear quickly.

There is 4 pages of "white board cyphering". If I saw you in the ditch, it's a simple let's see what we can do. I would try and get you out. instead of burning daylite.

[Rob]

Thanks for the links Ghost, good stuff.

My main interest is trying to understand the principles behind all this, gear selection, and I have been wondering how to determine impact of pull on anchors. 

Real life would be more along the lines of try direct pull and see if that works, then add a block, etc as mentioned.  If I need to winch, I won't be breaking out the pen, paper and calculator.   But being aware of potential danger points associated with excessive load on inadequate anchors seems like a wise bit of education to have. 

Ihave built a lot of climbing anchors and trusted them with my life - but I was sure to understand the principles first!

[ghosthunter]

Thanks for the links Ghost, good stuff.

My main interest is trying to understand the principles behind all this, gear selection, and I have been wondering how to determine impact of pull on anchors. 

Real life would be more along the lines of try direct pull and see if that works, then add a block, etc as mentioned.  If I need to winch, I won't be breaking out the pen, paper and calculator.   But being aware of potential danger points associated with excessive load on inadequate anchors seems like a wise bit of education to have. 

Ihave built a lot of climbing anchors and trusted them with my life - but I was sure to understand the principles first!

I am in the process of real life trail right now. I decided to take on a large Mt. Ash stump in my front yard. I could have it ground down but figured since I am retired I would see what a 71 year old guy could do with it.

I dug two feet deep around it today.
The stump is 3 ft across and the root ball is 10 ft across.

I hooked my truck to it straight pull and just tugged on it some while a buddy watched . No joy.
He said it rocked a little but not much. We figure it has about 800 lbs of dirt on it. So tomorrow I am going to try to get the dirt off the back side and lighten it up.

Than I am going to position my drop gate trailer next to it and try to winch up into the trailer with one block. Add blocks as needed.

I will be using my portable winch rated 2K straight pull.

I will post how it goes. Might take me a few days.

[MountainWalk]

Sounds like you need some giant powder. Or a hoe

[Magnum_Willys]

You are going to need a lot more blocks and rope !    I've done some big stumps and pulled out with a truck and snatch strap after a lot of digging - figure 30,000 lbs.
Problem is wood has a tensile strength of about 4000 psi - that means a 2" root can resist 12000 lbs before breaking. 

[ghosthunter]

You are going to need a lot more blocks and rope !    I've done some big stumps and pulled out with a truck and snatch strap after a lot of digging - figure 30,000 lbs.
Problem is wood has a tensile strength of about 4000 psi - that means a 2" root can resist 12000 lbs before breaking.

Yeah I knew it would be a chore. But I am stubborn. My plan is to dig as much dirt as I can from under it tomorrow than give it a try. If that doesn’t work I will Witt let it down with my chain saw. Stand by.

MT. Ash does not appear to have a tap root. I am fairly confident that I got all the roots cut today. The tree was dying and we had it cut down two years ago. It did sprout some shoots.But the large roots 6 inch or more were all rotted.