Ropes and knots are very important when using mechanical advantage.
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Carefulness costs you nothing. Carelessness may cost you your life.

Mechanical Advantage
Ropes and Knots
When applying mechanical advantage (MA), the rope and knots are as important as the pulleys.  

You will need more rope to make more force.  For example, a 5:1 mechanical advantage will need five feet of line for every one foot gained.

Anytime a knot is tied in a rope, the rope is weakened.  In drop tests and pull tests, a rope typically breaks at the knot. Attaching the pulleys to the pull line with midline knots reduces strength. A better option is to use a separate Prusik cord or a hitch such as the Valdotain Tresse Knot (VT).  This  retains rope strength while allowing adjustment.  Phillip Kelley will show you how to do a modified VT in the video below.

In  MA systems, there should be some form of control in case the pulleys meet and become two-blocked.   The load must to be held in place until a new pull can be made. Attaching the pulleys with a Prusik cord will hold the load while attaching the other end of the MA system using a separate rope and tying a VT allows for one pulley to be slid away from the other. The video below demonstrates this.
Valdotain Tresse Knot for Climbing and Rigging
Phillip Kelley of North American Training Solutions demonstrate a fast easy VT that you can use to tie on to the pull line. 
Mechanical Advantage: Part 2

This great little video demonstrates how the VT and Prusik knots can be used to correct two-block.

Upcoming Events

Saw Safety Team:  Ellen Bauske, Wade Hutcheson, Heather Kolich, Brian Maddy, Gary Peiffer, Rolando Orellana, and Phillip Kelley.


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Georgia Center for Urban Agriculture · 1109 Experiment St · Urban Ag · Griffin, Georgia 30223 · USA