5.2.15 Construct simple MA
5.2.17 Construct compound MA

Mechanical Advantage with Pulley Systems
There are three categories of mechanical advantages using pulleys; Simple, Compound, and complex.  A Simple MA consists of a pulley system that has a single haul connection between the load and the haul team.  A Compound MA is a simple mechanical advantage system pulling on the haul line of another simple mechanical advantage.  Multiplying the two systems will give the total advantage.
Here are five rules that can be used to determine simple and compound mechanical advantage systems.
1.  If the pulley closest to the haulers is on the anchor, the pulley is only considered a change of direction (cd). Same rule applies to ANY pulley system.
2.  If the rope used in the pulley system is tied to the anchor, the ideal mechanical advantage (IMA) will be EVEN (i.e., 2:1, 4:1. 6:1, etc.)
3.  If the rope used in the pulley system is tied to the load, the ideal mechanical advantage (IMA) will be ODD (i.e., 1:1, 3:1. 5:1, etc.)
4.  To determine the IMA of a simple pulley system, count the ropes between the anchor and the load. Do not count the ropes between two anchors.
5.  A simple MA pulling on the haul line of another simple MA is called a compound MA system.

A Complex MA system is neither simple or compound, and the above rules will not work in determining the system.  The only way in determining the mechanical advantage of a complex MA system is by calculating the "tension units". (See “Critical Thinking On Mechanical Advantage Systems” at the end of this section.)   The combinations of pulleys that can be incorporated in an MA system are infinite.  With this in mind, how many pulleys are needed, and what are the characteristics of a quality haul system?  

In general, the ideal mechanical advantage (IMA) is the ratio between the distance the load moves and distances the haul team moves. In a 2:1 system the load will move 1' to every 2' of haul.  However, this does not mean that lifting the load is twice as easy.  The practical mechanical advantage (PMA), or simply put, the efficiency of the system, is the actual physical advantage the haul team ends up with.  In short, based on the size of the haul team, try to build the MA system as small as possible.  More pulleys create more friction, resulting in efficiency loss.

Consider the hauling field; that is to say, configure the MA system in a way that maximizes that amount of ground area the haul team can operate.  This will also minimize the number of re-sets of the haul system.  Build the MA system clean.  Avoid crossed or twisted lines, as this will add unwanted friction in the system.

When the haul prusik slips this is an indication that something is not right.  Do not add an additional prusik, correct the problem.  A slipping haul prusik as like having a pressure relief device in the system, the haul prusik typically slips between 800 and 1200 pounds.  With the exception of tandem haul prusiks on a tensioning system for a "highline" operation, putting tandem haul prusiks in the MA is like replacing a 15-amp fuse with a 30-amp fuse, something could very well fail.

A "ganged on" MA system is separate from the main line.  An "integral" MA system is built with the same rope as the main line, and runs continuous from the load to the haul team.  Each way offers advantages; the "integral" system is less equipment intensive.  "Ganged on" systems can be pre-rigged, and moved into place speeding the change over from a lowering system to a raising system.  A ”piggyback” MA is a compound system that consist of two or more identical simple mechanical advantages, i.e., a 2:1 pulling on a 2:1 equals a compound “piggyback” 4:1.

Pulley Systems for Hauling, Lowering, and Holding
Rope rescue requires rigging skills to either move things or hold things in place.  As simple as this sounds, a complete working knowledge of pulley systems and mechanical advantage is a must.  Pulley systems used for lifting a load horizontally are somewhat different than a pulley system or mechanical advantage used to back-tie a tree or guy a high directional.  In addition to hauling and holding, a third type of pulley system is used for rapid changes from a hauling system to a lowering system. The difference of all these examples is the position of the ratchet (progress capture device).  

1.  Hauling pulley systems are designed to hold the load during resets of a hauling operation.  The ratchet is on the leg of rope directly connected to the load.
2.  Hauling, Lowering and Rapid Response pulley systems may be used up or down very quickly The ratchet is on the change of direction.
3.  Back-tie pulley systems are designed to maintain tension between two anchor points (May use only carabiners as pulleys).  The ratchet is on the change of direction. 

Other Considerations

• Rope and Equipment ---How much rope, pulleys, carabiners and other needed equipment is available?

• Size of the Load (output) ---What and how much weight is required to lift?  Is it a single person, or a rescue or extreme rescue load?

• Number of Haulers (input) ---What are the man power resources available for hauling?

• Work Area---What is the size of the work area for the team to safely operate?

• Throw ---What is the distance the MA system can operate before a reset?

• Incline of the Hauling Field---Is the hauling field level?Downhill hauls are much easier than uphill.

• Adaptability---Can you easily change to a larger or smaller mechanical advantage?

• Lowering ---Can the pulley system be employed as a lowering system?

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Clarification of MA Terms
Integral Versus Ganged On; Plain and simple, if its built with the one rope that is connected to the load it is a integral system, this may be a simple, compound, or a complex system.  A ganged system is an MA  which is built with a separate rope that is attached to the working rope.

Ganged On Versus Piggyback; A piggyback system is a compound MA that is made up of two or more identical simple MA’s. i.e. a compound 4:1 (2:1)(2:1).  A Ganged MA system is attached by a haul grab to a second main rope for the purpose of lifting or lowering a load. 

Change of Direction Versus Directional; A change of direction is a pulley on the anchor closest to the haulers, notated (cd).  A cd adds no mechanical advantage to the system.  A directional is a pulley or pulleys between the pulley system and the load to be raised, notated (d) or (1:1)

Throw Versus the Haul Field; The throw is the available distance between maximum pulley system extension and two-block (Note: Simple pulley systems have only one throw. Compound pulley systems have a minimum of two throws) The haul field is the available distance a hauler or haulers can run out or the space that they have to stand and pull. 

Simple Pulley Systems
Simple pulley systems must be considered one of the primary tools of rope rescue work. Some of the advantages are; they are easy to remember and perform. They have long throws and are easily modified if more advantage is needed. The disadvantages are, they typically have more friction, use more rope, and require more equipment in larger MAs.