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Haul Systems

Haul Systems and Mechanical Advantage
                                                                                                  - Jim Simmons

In related articles you can find information on knots and on setting suitable anchors for haul systems. You can also click on the site by Grog to review a variety of knots.
In spite of our best efforts when paddling, sometimes we have to deal with a stuck or pinned boat. Due to modern whitewater boat designs and materials boats seem to pin less than in earlier times when fiberglass and aluminum craft were commonly used. Modern open canoes usually are much smaller in size and are outfitted with maximum flotation which also helps prevent pins as well. Because of highly popular creek boating, whitewater kayaks will more likely pin or get stuck in vertical positions in narrow creek streambeds strewn with numerous boulders. A paddler entrapped in a vertical pin can present a serious situation for rescuers, however, this discussion will concentrate on more common horizontal boat pins.
 
Let's assume that the paddler(s) are safe and that we're dealing with a horizontal boat pin, say a whitewater canoe. It is always wise, initially, to access the boat and determine what needs to be done to free it. This might simply be just using sheer muscle power to lift or dislodge a boat. If the boat cannot be manhandled without rope systems, at least form a clear picture of how to apply a haul system using mechanical advantage. Common haul systems using mechanical advantage are always presented in our ACA swifwater rescue workshops and are a lot of fun to practice. (A haul system will require items that participants are asked to bring to a 2-Day SWR workshop: prusick loops, locking carabiners, one-inche tubular webbing).
 
Mechanical advantage may be defined as "a measure of how hard we need to pull or push to move a load or weight;" or, M.A. "applies more force to the load (pinned boat) than to the system." Because friction is a drag in any M.A. system there are a couple of main concepts we want to bring to your attention: a) in an 'ideal' system there will be almost no friction; and b) in 'reality', however, any haul system will have some friction. For example, if we're using pulleys in our haul system there will be much less friction than if we are using carabiners as pulleys...ideal vs. real. One writer/researcher has worked out these percentages of friction when using pulleys compared to using carabiners. With pulleys there is 93% of 100% (minimal friction); but with carabiners 67% of 100% (100% of course representing no friction).

A basic equation for describing mechanical advantage MA = Output Force
                                                                                                                               Input Force

3:1 Z-Drag.  See figure below                           *(work in progress, please bear with us)


Besides the traditional Z-Drag (3:1), other common systems used to unpin boats are both 2:1 and 4;1 mechanical advantage systems, especially a 4:1 piggyback system. Such piggyback hauls systems can be set on the main haul rope with one throw bag and are fast to deploy.


Piggyback System.  See next figure        *(work in progress, please bear with us)

Vector Pull
Another important strategy, a vector pull, is a perpendicular pull in the center of a line that is under tension. Some call a 'vector' as a way to apply "free" mechanical advantage.  See the figure below--

    *(work in progress, please check back later)

Pushing or pulling on a taut line, directly in the center, applies considerable force to each end. The tighter the loaded line the better the vector will work because one end or the other has to move. With a pinned boat, if the line is anchored well on shore (say with a 'bombproof' anchor such as a large tree) the vector will likely dislodge the pinned boat (assuming the line does not break). Pulling at vector also changes the angle of pull and that alone may shake loose a pinned craft.

You can demonstrate the effectiveness of a vector pull by having two friends pull strongly at both ends of a line while you apply a vector pull (using just one finger) in the middle between them. 

We will demonstrate another method of using vectors in our workshop.  It is a 'two-rope' trick with two ropes attached to a pinned craft and is a quick and easy way to unpin a craft without using intricate rope systems.

Haul systems using mechanical advantage don't have to be complicated but they do have to be practiced. Set up the systems on dry land, study and review them and then practice some more. The challenge is not just in memorizing one way to execute a system; the challenge is understanding the principles involved. If you can do that you have a true advantage. Happy pulleying!

JS--2/'10
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