We investigated the effects of the commonly used, yet potentially highly destructive bleach on rope strength. Samples of New England Ropes half-inch nylon dock line were pre-stretched 10 times to about 10 percent of rated strength (850 pounds) to simulate initial use. They were then treated with bleach, as presented in the table above. Samples that were treated more than one cycle were allowed to dry and set for 24 hours in a dry state before the next cycle. The samples were then pulled 10 times to about 50 percent of rated strength (4,250 pounds) before being pulled to failure.

Simple washing reduced the strength of the line 7 percent; the removal of spinning lubricants likely reduced the strands’ ability to equally share the load. Bleach, whether applied as concentrate for 20 minutes or as an overnight soak, reduced the line strength an additional 4 percent. Most destructive was repeated bleach and dry cycles, reducing strength up to 18 percent beyond simple washing. We presume this is because it was very difficult to completely remove the bleach at the end of each cycle—ropes are very thick in comparison to clothing—and as a result, the bleach dried in place, increased in concentration, and did more damage.

Samples of each type were retained for testing in one year. Will additional time, just sitting and aging, make a difference? We’ll let you know.

Riggers report bleach-destroyed lines every spring. It seems probable that older lines may be more vulnerable to damage than new line.

LINE CARE: Bleached Line* Breaking Strength