Breaking Strength of Rigging Knots

2008 | Brian Kane, University of Massachusetts

Rope is arguably the most important tool in the tree care industry.  Arborists use rope in many ways and its design has improved dramatically from the days of 3-strand manila climbing lines.  The ANSI Z.133 Standard requires that all climbing lines have a minimum breaking strength of 5,400 lbs., but knots reduce rope strength even when it is new.  There are few empirical data to describe the strength loss of arborist ropes that have been knotted, and knots are assumed to reduce rope strength significantly (i.e., up to 50%) (Blair 1998).  These guidelines, however, appear to be based on studies from other disciplines (e.g., rock climbing or sailing) or from manufacturers’ data.  Most of these data come from standard tests that do not include the knot in similar service as it would be in the tree care industry.  Following work by Samson and ArborMaster (Nulle 2004), we testing breaking load and specific strength of commonly used rigging ropes and knots.  Hitches were tied around a utility pole to simulate field conditions, and tested with gradually increasing loads. Breaking loads were similar among all hitches, but varied widely among ropes. Specific strength also differed among ropes and hitches. While tying hitches around tree-sized poles mimicked the arboricultural application of hitches and ropes, the static application of load did not reflect dynamic loads often generated during rigging of live trees.

Read the Research >

Year: 2008

Funding Duration: 1-3 years

Grant Program: John Z. Duling

Grant Title: Breaking Strength of Rigging Knots

Researcher: Brian Kane


Key words: Rope strength; breaking load; hitch; specific strength; knots;

Peer Reviewed Publications from Grant:

  • Kane, B. 2012. Breaking load of hitches and ropes used in rigging. Arboriculture & Urban Forestry 38:1-5.
  • Kane, B. and H.D.P. Ryan. 2012. Rigging ropes and hitch strength. TCI 23(3):RS1-RS5.

General Audience/Trade Publications: none

Presentations: none

For more information on this project, contact the researcher via TREE Fund at