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# The 9:1 Base Pulley System

Posted by Slack Science on Monday, 14 November 2011 in Gear Use

Recently, there has been quite a bit of chatter about the 9:1 base pulley system on the internet, so I thought I would write an all-inclusive article on the various methods and techniques of 9:1 pulley systems.

Before we get started, I want to make a few definitions that will help through-out the article:

1. Moving Pulley: In a slackline pulley system, there are typically two main pulleys: the moving pulley and the static pulley. The moving pulley is the pulley that is connected directly to your slackline. This pulley will progressively move closer and closer to the static pulley as you add tension to the line. This is the point in your system where all the mechanical advantage is being achieved.
2. Static Pulley: The pulley that is attached directly to your anchor point is called the static pulley. This pulley is doing nothing more than redirecting the ropes leaving the moving pulley.

For clarification, the base 9:1 pulley system is characterized by the mechanical advantage that is achieved by just the main pulleys in your pulley system. With a 9:1 base pulley system, every pound of force that you apply to the last strand of rope going to the brake, you are adding 9 pounds of force to the connection point of the moving pulley.

Also remember that the best way to add mechanical advantage to your pulley system is with multipliers, not additions of extra pulleys to the main pulley system. The main reason why one would use a 9:1 base pulley system over a simple 5:1 base pulley system is to minimize the load that is applied to the brake. In a 5:1 pulley system, the brake is holding 1/5th of the force that is on the slackline. With a 9:1 base, the brake only sees 1/9th of the total force. This is especially important when a LOT of force is needed (i.e. longlines). Keep in mind, if you have a phenominal brake (like the CMC MPD), then there is no need to use a 9:1 base pulley system because the brake is more than strong enough to hold 1/5 of the load of any slackline you could ever rig.

Okay, now on to the juicy stuff!

All methods of 9:1 base pulley systems that are used today require two sets of Main Pulleys (4 double pulleys total). The kind of pulleys you get totally depends on the type of 9:1 base you are aiming to do. There are two main types of 9:1 pulley systems that are widely used in the slackline world: the Side-By-Side 9:1 Base and the Embedded 9:1 Base. Both of these methods are highly efficient when used with quality Pulleys (like the ones in the BC Shop). I will define each below and explain the benefits of each.

### The Side-By-Side 9:1 Base Pulley System

The defining characteristic of this type of 9:1 base pulley system is that the moving pulleys are rigged side-by-side in such a fashion that it looks like a pulley with 4 sheaves rather than two double pulleys (see picture below).

Typically people use four of the same type of pulley for the side-by-side method, but this is not necessary. You can use any four double pulleys you'd like, as long as they sit nicely together on the shackles that you choose to use. I highly suggest using four of the SMC 3" Double PMP's, as they are the most efficient rigging pulleys out there and they sit very nicely together when rigged as explained below.

Out of the two 9:1 base methods, this is definitely the most efficient (when using four of the same large pulleys, like the SMC 3" Double PMP's). Unlike the embedded 9:1 base, the ropes that are traveling through the sheaves on the moving pulley side are all going over large sheaves. This ensures the least loss of mechanical advantage due to friction. It is possible to achieve this same mechanical advantage using an embedded pulley system, but you must use a special technique that I will not go into in this guide (basically using four of the SMC 3" Double PMP's embedded inside eachother and twisted).

So, how does one go about rigging with a side-by-side 9:1 base pulley system? Well, there are quite a few ways to set this system up. On the static pulley side, you can either rig with rigging plates or by using a seperate anchor for the brake and pulleys (as described in the Connection Point Article). I always like to use the rigging plate method because it organizes all my rigging and allows me to only have one anchor sling, which is handy when you have to put your anchors WAY up on the trees. I use two SMC Large Rigging Plates, mainly because they will sit on the bolt-side of a shackle MUCH better and it's also much stronger.

Next, you will need two 5/8" Van Beest Bolt-Type Shackles: One to anchor your rigging plates to the spanset, and one to connect your pulleys to. Notice in the picture below that I've attached the rigging plates to the anchor with one of the rigging holes on the rigging plates. This is because the eye of the shackle will not fit through the rigging holes, so I've turned it around.

Now, pass the second Van Beest Shackle through the anchor hole of the two rigging plates and leave the bolt off.

Now we will lay out our pulleys as we will have them in our pulley system so that we can thread the rope through. When laying the pulleys out, be sure to have the flat side of the main bolt of the pulleys pointed towards eachother so that they can sit as close to eachother as possible.

Okay, now we will thread the rope through. If you are sitting with the four pulleys layed out in front of you, then you will want to start your rope on the becket of the pulley closest to you on your left. You can use a 5/16" Stainless D-Shackle for this connection point. From this becket, you will take the rope and pass it up through the closest sheave of the closest pulley to your right. Follow this rope back to the left pulley and pass it down the sheave that is closest to you. Then proceed to the second sheave of the closest right pulley and pass the rope up through. Continue in this manner until you get to the last sheave of the furthest left pulley. The rope should be leaving the bottom of this pulley. This is the strand of rope that will be going to the brake. Leave your pulleys with the rope threaded through.

Keep in mind that the two pulleys on your left will be the moving pulleys and the ones on your right will be the static pulleys.

Now we will need two 7/16" Forged 316-Stainles D-Shackles to connect the two static pulleys to the Van Beest Shackle on the rigging plates. Other types of shackles that can be used include /16" Chain Shackles, or 1/2" Stainless D-Shackles. Now pass the one of the D-Shackles through the anchor hole of one of the static pulleys such that the threads are on the same side as the flat side of the main bolt on the pulley. This is so that you can correctly attach it to the Van Beest Shackle. See pictures below for explanation. Please note that the shackles used in the pictures are 7/16" Van Beest Chain Shackles (available upon request).

Be sure that when you attached the pulleys to the rigging plate that the last strand coming from the furthest left pulley is on the bottom, as in the picture below.

Please note that the above picture has been mirrored so that the ropes are not reeved correctly. Now we can attach the brake to the bottom rigging hole on the rigging plates. I like to use a single 1/2" Omega Pacific Steel Carabiner to attach to the rigging plates, then a 3/8" quicklink to attach the brake. This will cause the brake to sit such that handle is facing downwards so that releasing tension is easy. Having the handle face downwards will also ensure that the tail of the rope coming from the brake is on the same side of the entire pulley system as the strand entering the brake. This will make multiplying the pulley system quite easy.

Now that we have the pulley system rigging, how do we attach it to our slackline for tensioning? Well, this entirely depends on what kind of Webbing Anchor that you are using. If you are using a Shackle Line-Locker Kit, then you can simply rig the line-locker on the bow part of the shackle and connect the pulleys to the bolt-side of the shackle in the same fashion as above (see picture for details).

This is not the most desirable webbing anchor to use for those instances where you are using your side-by-side 9:1 base pulley system. You should be using an Alpine WebLock or similar device because of the high tensions involved with slacklines rigged with the side-by-side 9:1 base pulley system. To attach the two SMC doubles to the AWL2 takes a bit of ingenuity. There are a few methods that I like to use that are all equally strong. The first would be to create a "Missing Link" from a strand of extra webbing you have laying around. Just create a 6-inch to 1-foot long sling that is comprised of several wraps of webbing then tied together with a water knot. Then you can use this sling to attach the AWL2 to yet another 5/8" Van Beest Bolt-Type Shackle, which is connected to the SMC Pulleys in the same fashion as the static side. See pictures for explanation.

The other way to connect the moving pulleys to the AWL2 is to take a 1/2" x 4" Grade-8 bolt with nut and several washers and pass it through the anchor holes of the pulleys as well as the anchor hole of the AWL2 (with the shackle removed). This method is nice because it gives you the flexibility to adjust the distance between the pulleys as well as have the pulleys directly connected to the webbing anchor.

Okay, now we are rigged! Here is a nice gearlist for convenience:

1. Main Pulleys: 4x SMC 3" Double PMP's
2. Brake: Petzl RIG
3. Attachment Point: 2x SMC Large Rigging Plates
4. Rope: 300 ft. or more of PMI 11mm Access PRO
5. Connectors:
2 or 3 5/8" Van Beest Bolt-Type Shackles
5/16" Stainless D-Shackle
2x or 4x 7/16" Stainless D-Shackles (coming soon to BC Shop). Other types of shackles that can be used include: 7/16" Chain Shackles or 1/2" Stainless D-Shackles.
1/2" Omega Pacific Steel Carabiner
OPTIONAL (for certain connection methods) - 1/2" x 4" Grade-8 Bolt with Nut and Washers (can be found at any hardware shop)
Please note that the above gear list does not include the multiplier components. For information on the gear required for this, please refer to this Slack Science Article

### The Embedded 9:1 Base Pulley System

The defining characteristic of this type of 9:1 base pulley system is having a set of smaller pulleys inside a set of larger pulleys (thus the 'embedded' name). There are various combinations of pulleys that will work for this type of 9:1 base pulley system, but the best (in my opinion) is having a set of Rock Exotica Machined Double Pulleys embedded inside a set of SMC 3" Double PMP's.

The main advantage of this type of 9:1 base pulley system is that it's extremely modular. Since you need two sets of double pulleys for this system to work, you basically are getting three pulley systems out of the same gear. You will have your small pulley system, which consists of the embedded pulleys and a brake. Then you will have your bigger pulley system for longer lines or rigging regular lines alone, which consists of the outer pulleys and a brake. Then you have your 9:1 base pulley system, which uses all 4 of your double pulleys together with a brake. This type of modularity is very nice if you like to rig a variety of different types of slacklines (trick, long, high, etc...).

Another advantage of this type of 9:1 base pulley system is that it's extremely easy to anchor to the webbing using existing techniques that are already used to connect a 5:1 base pulley system to the webbing.

Also, this method is significantly lighter than the side-by-side method, simply because you are using only 2 large double pulleys and 2 smaller ones.

So, how does one rig the embedded 9:1 base pulley system? Well, there are number of ways to do it. To start, I will assume that you like to use the rigging plate technqiue for attaching your static pulleys to the anchor. Again, I like to use double SMC Large Rigging Plates for the static pulleys for strength and aesthetic reasons.

We will start with a single 5/8" Van Beest Anchor Shackle to connect the double rigging plates to. You can attach the shackle directly to the anchor hole of the two plates.

Now we need to thread the rope through our pulleys. Lay the pulleys out such that the SMC Doubles are on the outside with the Rock Exoticas on the inside like the picture below.

Now, attach the rope to the becket of the Rock Exotica Pulley on your left using a 5/16" Stainless D-Shackle. Then take the rope and pass it up through the furthest sheave on the right Rock Exotica Pulley. Then pass the rope down the furthest sheave of the left Rock Exotica Pulley on your left. Then up through the closest sheave on the right Rock Exotica Pulley. Then down through the closest sheave on the left Rock Exotica Pulley. Now take the rope and pass it up the closest sheave on the right SMC Pulley. Then down through the closest sheave on the left SMC Pulley. Continue like this two more times and you will have the tail coming out of the bottom of the furthest sheave of the left SMC Pulley. See pictures for details.

Now that the rope is threaded through the pulleys, we must attach the inner pulleys to the outer pulleys. I like to use 5/16" Stainless D-Shackles for this connection point because of their low profile. Be sure to not twist the inner pulleys before connecting them.

Now that the pulleys are connected, we can attach them to the rigging plates. Take a 1/2" Van Beest Anchor Shackle and connect it to the top rigging hole on the double rigging plates. This is where the pulleys will be connected.

Be sure that when you attached the pulleys to the rigging plate that the last strand coming from the furthest left pulley is on the bottom, as in the picture below.

Now we can attach the brake to the fourth rigging hole on the rigging plates. I like to use a single 1/2" Omega Pacific Steel Carabiner to attach to the rigging plates, then a 3/8" quicklink to attach the brake. This will cause the brake to sit such that handle is facing downwards so that releasing tension is easy. Having the handle face downwards will also ensure that the tail of the rope coming from the brake is on the same side of the entire pulley system as the strand entering the brake. This will make multiplying the pulley system quite easy.

To attach the embedded 9:1 base pulley system to the webbing anchor, you can use any technique that you have used to attach your 5:1 pulley system to your webbing. The AWL2 will connect directly to the SMC 3" Double PMP, as will the carabiner line-locker kit. Most other webbing anchors will have equally easy methods for attaching to the embedded 9:1 base pulley system. Any questions about specific webbing anchors can be asked in the comment section below.

Okay, now we are rigged! Here is a nice gearlist for convenience:

1. Main Pulleys: 2x SMC 3" Double PMP's and 2x Rock Exotica Machined Double Pulleys
2. Brake: Petzl RIG
3. Attachment Point: 2x SMC Large Rigging Plates
4. Rope: 300 ft. or more of PMI 11mm Access PRO
5. Connectors:
5/8" Van Beest Bolt-Type Shackles
3x 5/16" Stainless D-Shackle
1/2" Van Beest Anchor Shackle
1/2" Omega Pacific Steel Carabiner
Please note that the above gear list does not include the multiplier components. For information on the gear required for this, please refer to this Slack Science Article

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• Jason Arkin Tuesday, 15 November 2011

In your experience using the "Side by side" and "embedded" method, which system provide the most ease in tensioning. Is the difference marginal or significant?

• Tuesday, 15 November 2011

The main advantage to using the Side-By-Side 9:1 Base method is the added ease of tensioning. With the four larger radius sheaves, you get MUCH more actual mechanical advantage compared to using the embedded method.

• Tuesday, 29 November 2011

Hi there,

I believe there is more convenient way to do a 9:1 pulley system using combined pulley systems. That is pulling 3:1 system with another 3:1 system. Then you get 9:1 in theory. How ever this system requires only 4 pulleys in the contrary systems above requires 8. That results in such math (assume that we have best pulleys with 95% efficiency):
With 4 pulleys: 9*0.95^4=7.33
With 8 pulleys: 9*0.95^8= 5.97
So combined system gives us 7.33:1 in real when system used above only (aprox.) 6:1

• Tuesday, 29 November 2011

Very true. There are many many ways to build much higher efficiency setups than the two described above, but this assumes that you have an extremely high strength braking device. The only reason we have more pulleys before the brake is so that we can reduce the load at this point in the system. The brake is typically the weakest link in your pulley system so it's always best to limit the load here for safety reasons.

The best possible way to obtain a higher mechanical advantage is through multipliers rather than adding pulleys. If we had a brake that was capable of holding 1/3 of the tensions we add to our slacklines, then your method would be best.

• Bradosaurus Monday, 30 January 2012

Also, whatever force is loaded onto the brake is first applied by a rope grab. By design, many rope grabs are not made to handle the dynamic forces of pulling on a system with a lower mechanical advantage ratio.

• Balance Community LLC Tuesday, 06 November 2012

This is a nice web site.  Good fresh interface and nice informative articles. I will be coming back soon, thanks for the great article.
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• Jeremy Beard Tuesday, 19 February 2013

You're attaching the figure-8 follow through to the shackle because it's smoother than attaching it directly to the pulleys, correct? That's the only thing that I'm not completely following.

• PANAGIOTIS ATHANASIADIS Saturday, 30 March 2013

I am fishing many interesting ideas from this site, so I feel obligated to contribute some, too. Supposing that one has two SMC3" and two P21-double pulleys, I think that it may be better (at least stronger) to put each pair side-by-side, namely: the two SMC3" pulleys together at the tree side and the P21s (as lighter) at the webbing anchor side. This way, a WLL of 16KN can be safely reached. Anyone who has tried it?

Guest Wednesday, 19 June 2013

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