Lowering Devices & Friction Management

Arborist Lowering Devices

Before the development of friction tools like the original Port-a-Wrap, friction was applied by taking wraps around the trunk of the tree. This method was very tough on ropes, hard to control the precise amount of friction, and put tree workers at increased risk.

Arborist lowering devices provide a way to apply friction to lowering ropes to bring down wood with greater control and safety, and less wear on ropes. With a Port-A-Wrap or other lowering device, wraps are taken around the cylinder of the unit. The more wraps taken, the more friction is applied. This enables a single person to control loads many times their own weight.

Compared to the traditional method of taking wraps around the trunk of the tree, a lowering device provides more consistent friction that doesn’t vary from one tree to the next. It is easier to let ropes run with control, and halt them again. A friction device can be tied off to allow the worker to let go and walk away from the rope.

Some devices such as the GRCS or the Stein RCW-3001 also have a winch option so they can be used to lift as well as lower, adding further utility.

Capstan Equation

Samson’s rope engineers gave us the table below to illustrate the force needed to prevent rope movement on the Large Port-a-Wrap. The weight of the load is listed in the left-most column, and the number of wraps across the top row. Cross-reference to see the pounds of force needed to prevent rope movement. Table assumes a coefficient of friction from 0.1 to 0.2.