Slackline Corner - Tensioning Methods, Introduction To The Pulley Systems - Part 1

So, after a long time I decided to post something and it happens to be a 2nd 'Slackline Corner' issue translated into english. I will try to translate all of them although it's a bit of work; I have 12 more to go. Besides 'Slackline Corner' translations, which is more gear-based topic, I will be posting lots of new and a bit older news, trying to make up for arrears.

Page 1

Page 2

PHOTOS DESCRIPTION:

Page 1:
- title photo: 'Jan Gałek on the 'Nun As Fuk' Highline' (photo by Wojtek Kozakiewicz)
- left bottom corner: 'Ratchet is a perfect method to tension 2" trickline webbings (on the photo preparing Surfline for the trickline contest during OutDoor Fait 2010) (photo: Jordan Tybon)',
- right top corner: diagram; 'Colors: yellow - Ellington systems, red - chain hoist, black - pulley systems, purple - ratchets', 'Krótkie slacki/trickline = short lines/tricklines' (auth: Jan Gałek),
- right bottom corner: diagram for the description of the main pulley system parts.

Page 2: I think it doesn't need translation ;)

TEXT:

"The slackline season is almost at its peak and it is about time to refresh our knowledge a bit with a series of Slackline Corner articles. The last publications were about highline rigging, and in particular, about highline tensioning methods. 
We have already learned the process of highline-tensioning; now it is time to take a closer look at all of the different slackline tensioning systems, and the subsequent methods that accompany them. This theme is, not surprisingly, quite broad, so in this article I will describe only the basic concepts of tensioning systems; in the upcoming weeks I will focus on the finer details in Slackline Corners and my blog at www.goryonline.com.

The choice of your pulley system should be based on few things; whether it is for a longline, highline or trickline, the type of the webbing you are planning to use, and, of course, if you’re going to tension alone or with some friends.

There are quite few slackline tensioning methods, such as:

• Pulley systems,
• Ratchets,
• Ellington systems,
• Chain hoists.

All of these tensioning methods can be used alone or together. For example you can combine:

a) Ratchet with ellington system,
b) Chain hoist with pulley system.

The use of a pulley system is the most universal method for slacklining. With it, you can tension tricklines, waterlines, longlines and highlines. Of course, this doesn’t mean that you will always use the same configuration; the greatest advantage of this method its variability. You can use each element for many purposes (especially during highline projects which involve ascending, rappelling and/or hauling gear). The other benefit is that each component is replaceable, and if something is worn out, you can simply replace the one piece and continue using the same equipment for tensioning longer and longer lines. All of the other tensioning methods have built-in limitations, which you cannot overcome; principally, most systems are not suitable for longer lines, or in case of chain hoist, the weight of the equipment.

Pulley systems are easy to modify. Depending on your needs you can change its efficiency, weight and size with minimal effort. To illustrate this better I prepared a diagram presenting the differences of the given tensioning methods.

As you can see the pulleys system can be employed in every situation. The chain hoist comes in 2nd because there is little physical effort required for a lot of force, such as would be necessary for longer lines, but it is definitely not the best solution in every scenario. On the other hand, Ratchets and Ellington systems are wonderful solution for tensioning tricklines or short longlines. In this Slackline Corner I plan to focus on pulley systems, because while they are the most versatile, they are also the most complex. The rest of the tensioning methods will be presented together with the pros and cons of each in future editions of Slackline Corner.

Despite its complexity every pulley system will contain certain basic elements, such as:

a) Main Pulleys (always double pulleys),
b) Static Rope (9-11mm diamater),
c) Locking device (such as Gri-Gri, Eddy etc.),
d) Connecting elements (steel carabineers, quick-links, shackles),
e) Multiplier [basic multiplier 3:1 consists: connecting element (for example carabiner), camming device (for example Tibloc from Petzl) and one single pulley].

Go to my blog if you want to find more precise description about these elements (post: ‘Longline Abecadło – cz. 1 Sprzęt’).

Below you will find the most important aspects to consider in order to choose the right elements:

Main pulleys – for slacklining it is best to use double pulleys aligned ‘side-by-side’, as opposed to linear pulleys (for example, the Petzl ‘Tandem, which is more suitable for ziplining then tensioning lines). ‘Side-By-Side’ alignment allows for a larger sheave without losing pulley stability, and it also allows you to keep your tensioning system nice and compact. A larger sheave diameter increases the mechanical advantage, which in the end means higher efficiency. The second most important criterion is the strength of your pulley. Most pulleys are rated to about 36kN, which is more than enough for a 100-meter longline. If you’re planning on setting up lines longer than this, it is a good idea to spend your money on something stronger; the best would be around 50-60kN. Another thing to consider is the type of bearings under the sheaves, the most effective being sealed ball bearings; they create the least friction even under big loads. If you are planning to use your pulleys in high, alpine projects, you should also pay attention to the weight factor because when you have to carry lots of gear, lighter is always better,

Static rope – while choosing your rope you should pay attention to few things like the diameter (it has to be compatible with your pulleys and locking device), and the strength (most static ropes range from 9-11mm diameter and are rated to 22-30kN, enough for slackline purposes). You should, however, follow the same rules with your rope as your pulleys: longer slackline = stronger rope. The strength of the rope will also depend on the kind of pulley system, more strands equals less force on each strand of rope (for example in a 5:1 system, the force generated is divided between the 5 strands of rope inside the pulley system, in a 9:1 system between nine strands, etc.). The next important criterion is the rope stretch – the smaller the better, but most static ropes are around 13-15%. The last thing you should pay attention to is the material and the way the rope is made. It’s important that your rope be resistant to friction, high temperature, cuts, etc.,

Locking device – the most common models used in slacklining are: GriGri, GriGri 2, I’D, Rig (all from Petzl) and Edi (from Edelrid). In the upcoming Slackline Corner articles, I will describe in detail the differences between these devices, what's important to note is a minimum of 15kN breaking strength and the ability to release the device under tension. You can also check my blog for some more useful info,

Connecting elements – inside your slackline system, there should be only steel elements. This means steel shackles, quick-links and carabineers, all rated higher than 30kN. It is extremely dangerous to tension a line with aluminum carabineers! Aluminum gear can have invisible fractures and when they fail, they simply break, unlike steel, which bends before breaking completely. The only exception is the multiplier carabiner. The most basic multiplier is 3:1. As the name suggests, it multiplies the mechanical advantage of our basic pulley system (more info about it on my blog and in the next Slackline Corner).

We can divide pulley system into separate types based on their mechanical advantage ratio. We have, theoretically, and infinite number of configurations, but for our purposes, there are four basic pulleys systems: 5:1, 6:1, 9:1 and 10:1.
What does it mean? And how you know which one is which? I will try to explain using a 5:1 system as an example. A 5:1 system means two double pulleys on either end, the rope traverses each pulley then twice making 4 strands, and the 5th is then the free end of the rope coming out of the brake device. When we pull on this free end coming out of our brake, we are generating 5 times more force than if we pulled directly on the end of the slackline (ignoring friction). I will not make it more complicated by explaining the exact physics behind it, but if we combine our 5:1 pulley system with 3:1 multiplier, at the end our set-up will reach ratio of 15:1 (5 x 3 = 15). Considering that every healthy man or woman, using their weight and strength, can generate at least 100kg of force, it means that using this equipment they can tension a line to around 15kN (1,5t)!

The second criterion for differentiating pulley systems is the way the locking device is attached to the pulley system itself. We can find:

• Pulley system in which the locking device and the pulley system are clipped to two separate anchors (for example, two different spansets on the same tree),
• Pulley system in which the locking device and the pulleys are connected to a single point, such as a rigging plate, which is then fixed to the main anchor,
• Pulley system in which the locking device is attached inside the system to the becket on the main pulley. It is really important to remember attach the locking device sideways so it does not rub against the rope or other elements. You can achieve that by using two quick-links or twisted U/D-shackle.

Stay tuned for more detailed descriptions of pulley systems coming up in the next Slackline Corner and on my blog.

Peace & SlackOn!"

Last but not least I want to thank my friend Jordan Tybon for spellchecking my english translation of the article and suggesting few ideas and changes!!

Peace & SlackOn!