(Go Back)Rigging Terminology

"Knowing the ropes" is only half the job.

Here's a quick primer on terms and concepts that can make you more productive and keep you out of trouble.

Breaking or Tensile Strength -
The amount of force that will break or distort the particular rope or component. It is commonly recommended in tree care to operate at no more than 10% of a product’s tensile strength.

Safety factor -
The ratio used to determine the Safe working load (SWL) or Working load limit (WLL) of a particular component. An example of a safety factor is ten to one, the tensile strength would than be divided by ten to arrive at a safe working load.

Safe working load (SWL) or Working load limit (WLL) -
This amount of force, arrived at by using the safety factor and tensile strength of the component, gives you a load limit that allows you to use the component safely for an extended period of time.

Cycles to failure -
The process by which repeated loading weakens a component in the rigging system. Ropes, connecting links, and other components are losing strength all the time through use. Loading them near their tensile strength will speed up this weakening process.

Bend radius -
The amount of bend formed in a rigging line when it passes over the branch in natural crotch rigging or the sheave of a block or pulley when using a manufactured anchor point. This bend weakens the strength of the rope, by compressing some of its fibers. A bend radius for braided ropes, such as Stable Braid or Arborplex, of 4 to 1 or greater will retain more of the rope's strength, and 8 to 1 would be preferred. Twisted ropes, such as TreeMaster, should have a bend radius of 10 to 1. For example a ½" Stable Braid should pass over at least a 2" sheave, whereas 1/2" 3-strand TreeMaster should require a 5" sheave.