B-2:1 with Ratchet
C-2:1 Pulling Second Rope
This system is nothing more than a force multiplier turned around. One end of the line is attached to an anchor. The rope passes through a pulley and back in the direction of the anchor. The load is suspended from the pulley. The load is equally supported by both sides. When you pull up on the unanchored side you only need extend one half the force, but for twice the distance. Figure A portrays this in the simplest form. Note that this form is considered unsafe for live or critical loads.
Figure B is the preferred method for hauling a live or critical load. In this system we have added a ratchet cam. The ratchet cam is used to hold the load when sufficient force is not being exerted on the unanchored end.
Figure C shows how to use a 2:1 system to pull on a separate line. In this system we use an ascender (called the haul cam) to attach the traveling pulley to the load line. We place a second ascender (called the ratchet cam) below the haul cam. By placing the ratchet and haul cam on the load line the team can pull up the load line with the hauling system, set the weight on the ratchet cam, and then reset the haul cam to take another bite and haul up more of the load line. This same sequence is used with all other systems.
3:1 The Z-Rig
The z‑rig allows you to exert only one‑third the force for three times the distance. Notice that the z shape must be maintained otherwise it turns into a simple direction change and offers no mechanical advantages. As force is applied to the unanchored pulley it will move towards the anchored pulley until they meet. Set the ratchet cam by slightly slacking the hauling system behind the ratchet cam. Then reposition the haul cam by moving it towards the load. Repeat this procedure until the load reaches the desired level.
4:1 Piggyback Rig
The piggyback is nothing more than a 2:1 system hauling another 2:1 system for a total mechanical advantage of 4:1. To set up a pig: divide the haul system line into two legs by tying a figure 8 on a bight at the mid point. Attach the knot to a suitable anchor. Use one leg to set up a 2:1 system with the haul cam attached to the load line. The free end of this 2:1 portion is terminated at the second pulley by attaching it to the carabiner hole on
the pulley. The other leg is used to set the second 2:1 system through the pulley with the terminated line. A ratchet cam is added to allow the team
to reset the hauling system.
A ratchet cam is used to hold the load while the haul cam is being repositioned. Do not consider the ratchet
cam to be a safety. Its sole purpose is to hold the load on a temporary basis. A ratchet cam may not hold
under shock or heavy loading. A potential problem is shock loading of the ratchet cam. This can occur as
the hauling team pulls the line through the system. An unanchored ratchet cam can move along with the
line, creating slack in the system (see Figures A & B). This slack can be the cause of a shock load to the
entire system. To prevent this from occurring a person, or shock cord can be used to prevent the cam from
moving as the line is hauled up as shown in Figure C.
Multi-Line Hauling System
This system is used to provide equal tension on two lines. Common uses are to pretension a dual line tyrolean traverse (highline) or to pull with equal force at several points on an object such as an overturned trailer that needs to be put back on its wheels. By adding additional anchored pulleys, traveling pulleys and ascenders this system can be adapted to pull on 3, 4 or more lines as needed.
Notice that the illustrations in this catalog show a number of different ascenders used as ratchet or haul cams. Mechanical ascenders or ascender hitches can be used to achieve the same end results. However, one must be aware that no system is 100% fail safe. Mechanical ascenders (Gibbs, Jumars, Petzls etc.) can cut the rope under high or shock loading. Ascender hitches have also been known to slip until the load comes to rest on a solid surface under the same conditions. There are no magic formulas one can give you that can tell you which type of ascender to use for any particular job. Do consider the manufacturers load ratings and recommendations when selecting mechanical ascenders. Temper this with training and practice before utilizing these techniques in the field.
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