what blocks/pulleys are you using for mechinal advantage ?

Joseph Hodgin

Joseph Hodgin

New member
What pulleys are you all using for a mechinal advantage (manufacture) ? Also, what rope with it? Just want to know and why. Thank you!
 
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Most times it's just to get a tree over the centre of gravity we will sweat the line. Hard tension by hand to an anchor then another line onto that line to create more than double the force. Dyneema core for the best progress and low stretch. Thanks Spyder where did you go?
 
mt43sj.jpg


I use this on the ground. It's easy enough to set a 3:1 to pull on the 5:1. You can get some serious tension on a pull tree. Usually pull a bunch of the stretch out of 5/8" Arborplex and let her rip.

14mm Sirus
Steel biners (ISC)
ISC double aluminum blocks.
Stainless shackle
Two prussiks for progress capture and adjustable link to the host line.
1/2" Pinto Rig loopie for setting the 3:1
Pinto Rig prussik for setting the 3:1. (not pictured)

Cheers
 
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My MA is rigged with 3/8" KMIII using rescue pulleys with stainless steel cheek plates.

Along these lines:

http://thumbs.ebaystatic.com/d/l225/m/mryKsTO8una4BH3KV9RstjA.jpg

I use a friction hitch to capture progress so one double sheave is a PMP with a becket.

When you're assembling your MA be sure to study the expected loads so that you size everything correctly. Most of the MA setups I've seen are WAYYYY overbuilt. One person can generate roughly 60% of their body weight in pull on a horizontal line. So...in rough terms...a 200# person will generate 120# pull. Then go through a 4:1 the person is only generating around 500# of pull. Configure that correctly with your chosen safety factor...some use 5:1 SF...so, 2,500# breaking strength in your system. That's end to end on the biners/connectors. No need to use large sheaves and rope if you calculate correctly.

These numbers are rough...do your own research and choose carefully.
 
Very good Tom. Also, watch out for the rope in the MA system when releasing tension, it can move deceptively fast through the pulleys and will burn/cut through clothing and skin easily.
 
Jack Pine said:
...watch out for the rope in the MA system when releasing tension, it can move deceptively fast through the pulleys and will burn/cut through clothing and skin easily.
Click to expand...

YES! Another reason I never use Tenex or the like for friction hitches in this application. Find cordage with a much higher melting point.

Keep fingers away from the friction hitch too. Way too likely to get between the hitch and the cheekplates...or get sucked into the sheaves...ouch!
 
Good point on the prussik cord. In line with that, we did a little destructive testing of 10mm AP with an old 5/8 line locked off and a vehicle pulling. The cover was fuzed to the host line, but the core was undamaged .

2nrlnoo.jpg
 
Jack Pine said:
mt43sj.jpg


I use this on the ground. It's easy enough to set a 3:1 to pull on the 5:1. You can get some serious tension on a pull tree. Usually pull a bunch of the stretch out of 5/8" Arborplex and let her rip.

14mm Sirus
Steel biners (ISC)
ISC double aluminum blocks.
Stainless shackle
Two prussiks for progress capture and adjustable link to the host line.
1/2" Pinto Rig loopie for setting the 3:1
Pinto Rig prussik for setting the 3:1. (not pictured)

Cheers
Click to expand...
Thats what I'm talking about! NICE!
 
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Tom Dunlap said:
My MA is rigged with 3/8" KMIII using rescue pulleys with stainless steel cheek plates.

Along these lines:

http://thumbs.ebaystatic.com/d/l225/m/mryKsTO8una4BH3KV9RstjA.jpg

I use a friction hitch to capture progress so one double sheave is a PMP with a becket.

When you're assembling your MA be sure to study the expected loads so that you size everything correctly. Most of the MA setups I've seen are WAYYYY overbuilt. One person can generate roughly 60% of their body weight in pull on a horizontal line. So...in rough terms...a 200# person will generate 120# pull. Then go through a 4:1 the person is only generating around 500# of pull. Configure that correctly with your chosen safety factor...some use 5:1 SF...so, 2,500# breaking strength in your system. That's end to end on the biners/connectors. No need to use large sheaves and rope if you calculate correctly.

These numbers are rough...do your own research and choose carefully.
Click to expand...
Thank you
 
Jack Pine said:
mt43sj.jpg


I use this on the ground. It's easy enough to set a 3:1 to pull on the 5:1. You can get some serious tension on a pull tree. Usually pull a bunch of the stretch out of 5/8" Arborplex and let her rip.

14mm Sirus
Steel biners (ISC)
ISC double aluminum blocks.
Stainless shackle
Two prussiks for progress capture and adjustable link to the host line.
1/2" Pinto Rig loopie for setting the 3:1
Pinto Rig prussik for setting the 3:1. (not pictured)

Cheers
Click to expand...
 
I'll get pics but I use bail out line I had at the fire station that was never used. 75'. 10mm. 2 small aluminum pulleys(eBay blue water ropes special $20 each) with a small Prussic as a lock off. Based on the Aztec system or the "set of fours". Basically all I would use it would be to pretension a load line. If I had to truly haul weight I'd just build a z drag with some x rings or blocks. Simple 3:1 will do most of what I need since he average adult male pulls 250lbs
 
Tom Dunlap said:
My MA is rigged with 3/8" KMIII using rescue pulleys with stainless steel cheek plates.

Along these lines:

http://thumbs.ebaystatic.com/d/l225/m/mryKsTO8una4BH3KV9RstjA.jpg

I use a friction hitch to capture progress so one double sheave is a PMP with a becket.

When you're assembling your MA be sure to study the expected loads so that you size everything correctly. Most of the MA setups I've seen are WAYYYY overbuilt. One person can generate roughly 60% of their body weight in pull on a horizontal line. So...in rough terms...a 200# person will generate 120# pull. Then go through a 4:1 the person is only generating around 500# of pull. Configure that correctly with your chosen safety factor...some use 5:1 SF...so, 2,500# breaking strength in your system. That's end to end on the biners/connectors. No need to use large sheaves and rope if you calculate correctly.

These numbers are rough...do your own research and choose carefully.
Click to expand...
Mr. Dunlap, thank you for you reply on this matter. Did you post 3/8th KMlll?
 
We have 5:1 block & tackle in each truck with a length of our rigging line through it. 150' 0f 1/2" samson db
 
Tom Dunlap said:
Most of the MA setups I've seen are WAYYYY overbuilt. One person can generate roughly 60% of their body weight in pull on a horizontal line
Click to expand...
Overbuilt, yes, but we often times don't pull out the MA because I need a little tug on something. 1 or 2 guys and a simple tag line can accomplish that. Many times we bust out the MA because we need to put some serious oomph on something (40" oak with a horrible back lean; wheel loader buried in mud up to the axles, etc.) I was taught roughly 2/3 of body weight on flat ground (whats a few percentage points among friends?) so my numbers match up well with yours. However, when we have 4 guys, pulling in unison (1, 2, HEAVE! 1, 2, HEAVE!) on a 5:1, we're talking 4*(2/3*200)*5 = 2600 pounds. In several cases we've had a 5:1 system pulling against a simple 2:1 system, and for the biggest baddest back-leaning silver maple I've ever tackled, we had two of the above mentioned 10:1 piggy-backed systems on it. Since each of the systems has a progress capture, the 4 guys would get as much tension on 1 setup as they could muster, lock it off, then switch to the other system and get another several feet rope out of it along with the corresponding inch or two of trunk movement. Lock off, drive the wedges in a little more and repeat the entire procedure.

As such, my MA system is Schaefer 7 series fiddle blocks (SWL 2250 lbs) threaded with Samson True Blue (fat and soft, so nice grip and easy on the hands) pulling against 50 kN steel carabiners. Doesn't seem quite so overbuilt in this light. Maybe I need to go shopping and beef it up a little...
 
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Jeff said:
Overbuilt, yes, but we often times don't pull out the MA because I need a little tug on something. 1 or 2 guys and a simple tag line can accomplish that. Many times we bust out the MA because we need to put some serious oomph on something (40" oak with a horrible back lean; wheel loader buried in mud up to the axles, etc.) I was taught roughly 2/3 of body weight on flat ground (whats a few percentage points among friends?) so my numbers match up well with yours. However, when we have 4 guys, pulling in unison (1, 2, HEAVE! 1, 2, HEAVE!) on a 5:1, we're talking 4*(2/3*200)*5 = 2600 pounds. In several cases we've had a 5:1 system pulling against a simple 2:1 system, and for the biggest baddest back-leaning silver maple I've ever tackled, we had two of the above mentioned 10:1 systems on it. Since each of the systems has a progress capture, the 4 guys would get as much tension on 1 setup as they could muster, lock it off, then switch to the other system and get another several feet rope out of it along with the corresponding inch or two of trunk movement. Lock off, drive the wedges in a little more and repeat the entire procedure.

As such, my MA system is Schaefer 7 series fiddle blocks (SWL 2250 lbs) threaded with Samson True Blue (fat and soft, so nice grip and easy on the hands) pulling against 50 kN steel carabiners. Doesn't seem quite so overbuilt in this light. Maybe I need to go shopping and beef it up a little...
Click to expand...
We run 2 or 3 man crews so 1 guy pulling any back lean I go for the 5:1 because if a 3:1 comes up a little weak half way through the pull that super sucks.

We keep our 5:1 ma together in the truck so it's not that hard to pull it out and set it up. Better to strong than to weak.
 
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