Mechanical Advantage Systems

 

www.youtube.com/watch?v=T1G3XmoaxSo

 

All of the knots used for these anchors can be found on the Rescue Knots page.

 

When We Use Mechanical Advantage

Rope and pulley systems are rarely needed in everyday paddling, let alone river rescues. However, when you do need mechanical advantage, you want to be able to set it up quickly, safely, and with the equipment that you have on hand.

In the whitewater setting, the most likely application for mechanical advantage (MA) systems is to haul on boats that are wrapped or pinned. They are also used to tension lines for transportations systems or for raising a subject or rescuer up a cliff face or steep embankment. 

Types of Systems

MA systems can be grouped into three categories: simple, compound, and complex. This article outlines 2 simple and 1 compound system. They are the ones practiced most often on our whitewater rescue courses because they are useful and easy for our students to learn and become confident setting up. 

That being said, there is no limit to the types of systems that can be used and an understanding of how the systems work will allow rescuers to improvise, make adjustments, and 'pull out' different systems depending on what the situation calls for and the resources available. The underlying concepts are the same in swiftwater rescue as the are for mountain, high angle, confined space, and any rescue discipline where technical rope systems are used.

New Best Practice

You'll see on these videos and diagrams that we always add a final change of direction to these systems so that pullers can stand outside of the 'impact zone' while hauling and limit the chance of being hit by flying hardware if something breaks. In the past, different strategies were employed, such as using dampers (like a PFD hanging from a pulley) or limiting the amount of pullers. By using the final change of direction, rescuers can keep their PFDs on, pull with as much force as is needed, and have no fear of flying pulleys.

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This is a simple 5:1 system with a final 'change of direction' pulley added so that pullers can stand outside of the impact zone when hauling.

Simple 5:1 Mechanical Advantage Pulley System

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Compound 9:1 mechanical advantage system with rope and pulleys

The compound 9:1 is a useful system because it requires just one more prussik than the simple 5:1 and the systems can be changed back and forth very quickly if a rescue team needs to 'shift gears'.

Simply add the additonal prussik to 'line #3" (the line that you would pull to have a 3:1 advantage) and then unclip the last 'traveling pulley' from the 5:1 and reclip to this new prussik.

 

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100% Waterproof and Tear-proof, the Whitewater Rescue Field Guide folds up like a small map to fit easily into your PFD pocket.

Whitewater & Swiftwater Rescue : Waterproof Field Guide

 

More on the Field Guide here.

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