Double Swing Pulley for a Double Pulley System

A double pulley puts two sheaves side by side in one frame, and this double swing pulley has side plates that open so you can load rope mid-line. It is the building block for a compact double pulley system: pulling over a tree, tensioning a speedline or hauling a heavy piece out of a ditch.

What a double pulley system does

Mechanical advantage lets one or two people put serious force on a rope. With two double pulleys, one anchored and one on the load, you can build a 4:1 system in a compact package. Add a progress capture or a friction hitch and you can hold what you gain. A single double pulley paired with a single pulley gives you a 3:1.

On tree jobs that means pulling a back-leaning tree over the notch, tensioning a speedline, or skidding a heavy log onto the trailer without a winch.

The compact frame matters in the field. Two single pulleys hanging side by side twist around each other and tangle; a double pulley keeps both rope parts in one plane and runs cleaner. Fewer separate pieces also means fewer carabiners to manage, which speeds setup and teardown on a busy day.

Why swing side plates matter

With fixed side plates you have to thread the rope through from the end. That is slow when the rope is already rigged with a running end tied off a hundred feet away. Swing plates let you open the pulley, drop the rope in, close it and clip it, all at the middle of the line.

Check that the plates close fully and the carabiner passes through both before loading. A pulley that is not closed can let the rope ride out under load.

Swing plates also make teardown fast. Once the pull is done, open the plates, lift the rope out and pack the pulley without pulling a hundred feet of line back through.

Building a 2 pulley system

The simplest 2 pulley system is a single pulley at the anchor and one at the load: rope tied off at one pulley, through the other and back, gives you 2:1 or 3:1 depending on where the end is tied. A double pulley at each end doubles the number of rope parts and the ratio.

Friction in each sheave eats into the theoretical advantage, so real-world output is less than the math says. Good bearings and correct rope diameter help. Keep ropes from twisting around each other between the pulleys, which adds friction fast.

More of the haul hardware is in our mechanical advantage section.

Safe use

Mechanical advantage can easily overload anchors, slings and the tree itself. Know the forces you are making, and use hardware rated for them. When pulling trees over, keep everyone clear of the fall zone and the line's path if something breaks. Rigging gear is not life support; keep it separate from climbing gear and train crews to ANSI Z133.

Inspect the pulley before each job: sheaves spin freely, no cracks or bends, side plates tight on the axle.

Store it clean and dry, and keep it in the rigging bag rather than loose in the truck bed.