Multiplier

Now that the basics of the pulley system have been covered we need to work in a little component that makes a huge difference when tensioning; the multiplier. The multiplier is an essential component in the pulley rig because it allows for 2 very important things; 1) increases your mechanical advantage by 3 times and 2) redirects the tail of the rope. This makes it so the rigger is standing behind the tree while tensioning; creating a safety barrier in case anything goes flying during the rigging process. In a typical 5:1 base pulley system with cam style brake, it’s not enough to pull the rope through the base system. The rigger will never be able to pull 1,200+ lbf of tension in the base pulley system alone. A multiplier is needed to increase your mechanical advantage in order to bring the line to tension

Standard style multiplier with single pulley, chest ascender and carabiner.

Standard style multiplier with single pulley, chest ascender and carabiner.

The multiplier is attached to the rope coming from the front pulley leading into the brake. The tail end of the rope coming out of the brake is then redirected through the multiplier pulley. Theoretically this multiplies the 5:1 base pulley system by 3 and turns it into a 15:1 system. With the added mechanical advantage the rigger can then bring the slackline to tension. To create a multiplier the rigger needs three things: 1) rope grab, 2) single pulley and 3) something to connect the two.

Multiplier Components

  1. The Rope Grab comes in different shapes and sizes but its main purpose is to grab or bite down on the rope when placed under tension and then be able to slide back to re-position for the next effort.
  • Prusik: The simplest and most inexpensive way to create a rope grab is to use a Prusik, Klemheist or Valodine Tresse knot. There are slight variations between these knots and all are considered auto-locking knots. They grab onto the rope when loaded in one direction and can release in the opposite. They can be cumbersome to build and release but are often worth the weight savings. Always monitor the prusik before, and after use because the material can wear through after long periods of constant use. Using a Technora rope as the rope grab can help reduce wear due to the properties of the material.
A minimalistic multiplier using a prusik as a rope grab.

A minimalistic multiplier using a prusik as a rope grab.

  • Tibloc: The Tibloc is a very small and simple piece of gear that is often misused and has unfortunately acquired a reputation of tearing up rope sheathes. If used, it is important not to abruptly yank the rope because the Tiblocs teeth can violently dig in and potentially tear your sheath. If used carefully, it is a good rope grab that weighs next to nothing. Furthermore, it is short and if used with a short carabiner and pulley makes for a compact multiplier. A shorter length multiplier will allow you to get more throw out of your pulleys because there is less hardware in the system.
  • Ascender: Ascenders are the easiest rope grabs to use and are widely available. They are great for heftier pulley systems and come in many shapes and sizes. One of the tremendous benefits of an ascender is that if your pulley is rigged high overhead you can attach a rope in the front connection point to help the pull to reset your multiplier; a very useful trick when rigging longlines overhead.
A selection of rope grabs. The handled ascender is no requirement, yet it makes tensioning a lot easier.

A selection of rope grabs. The handled ascender is no requirement, yet it makes tensioning a lot easier.

2. The Single Pulley can be any sufficiently strong pulley. It is worth mentioning that the multiplier pulley makes a huge difference in the system when looking at theoretical mechanical advantage. That means if the rigger uses an efficient pulley like a SMC 3’’ single PMP he/she’ll get the most out of any system. But practically speaking, this may not be the place you’d want a giant clunky pulley to be.

3. The Connector usually is an aluminum carabiner. This is the only place within a slackline pulley system where it is appropriate to use an aluminum carabiner. It only sees small tensions and does not stay in the greater system when walking. It therefore can be light and doesn't need to be over-dimensioned (for weight’s sake.) If the rigger decides to use a prusik style multiplier, this component typically is not necessary.


Visit us at 508 international to attend a clinic & get instruction

new england's only adventure sports playground!