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#101564 - 08/04/07 01:01 PM Re: Rope pully system. [Re: Alex]
Enter_Narne Offline
Stranger

Registered: 09/16/06
Posts: 12
If instead of simply putting the rope through the last loop, he made another pulley-loop and then went back around the tree, would he multiply his force yet again?

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#101565 - 08/04/07 01:07 PM Re: Rope pully system. [Re: Todd W]
Susan Offline
Geezer

Registered: 01/21/04
Posts: 5163
Loc: W. WA
That's great... as long as you've got a post or tree nearby.

Sue

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#101568 - 08/04/07 01:20 PM Re: Rope pully system. [Re: Enter_Narne]
OldBaldGuy Offline
Geezer

Registered: 09/30/01
Posts: 5695
Loc: Former AFB in CA, recouping fr...
Probably, at least in theory. Should really increase the friction too. If you are going to rely on this, I would suggest buying some real pulleys, and a short section of rope/strap to secure one to the tree with...
_________________________
OBG

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#101572 - 08/04/07 01:24 PM Re: Rope pully system. [Re: OldBaldGuy]
Enter_Narne Offline
Stranger

Registered: 09/16/06
Posts: 12
I agree with having real pulleys, but I'm trying to find out what the possibilities are with just a rope. You may find yourself in a situation with only a rope to pull a car out of the mud.

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#101573 - 08/04/07 01:26 PM Re: Rope pully system. [Re: Enter_Narne]
OldBaldGuy Offline
Geezer

Registered: 09/30/01
Posts: 5695
Loc: Former AFB in CA, recouping fr...
"...with only a rope..."

In that case, rig this thing up, and good luck...
_________________________
OBG

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#101608 - 08/04/07 09:04 PM Re: Rope pully system. [Re: OldBaldGuy]
bsmith Offline
day hiker
Addict

Registered: 02/15/07
Posts: 589
Loc: ventura county, ca
_________________________
“Everyone should have a horse. It is a great way to store meat without refrigeration. Just don’t ever get on one.”
- ponder's dad

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#101720 - 08/06/07 12:54 AM Re: Rope pully system. [Re: MichaelJ]
thseng Offline
Old Hand

Registered: 03/24/06
Posts: 900
Loc: NW NJ
WARNING-WARNING-DANGER-DANGER

Under any serious load, the moving part of a nylon rope will very quicky melt/saw right through the stationary loop it is running on. Run the rope over a metal carabiner instead.
_________________________
- Tom S.

"Never trust and engineer who doesn't carry a pocketknife."

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#101806 - 08/06/07 07:22 PM Re: Rope pully system. [Re: thseng]
paramedicpete Offline
Pooh-Bah

Registered: 04/09/02
Posts: 1920
Loc: Frederick, Maryland
He has basically created a 3:1 Z-rig without the use of pulleys. The system will work for short distances, but as already noted, there is loss of mechanical advantage due to the rope on rope friction.

Rope on rope is not ideal, but we utilize this method when creating static back-ties on questionable anchor points such as small trees, poles, etc. We tie the back-tie line (high up, as well as the main or belay line – generally you keep you anchor points low to create sheer force instead of lever force, but when back-tying high, the vector forces will be directed downward) to the tree/pole, place a butterfly knot in the line about ˝ back and then run the line around the base of a smooth, but sturdy tree/pole and take the running end back through the butterfly, thus creating a 2:1 mechanical advantage.

Pete

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