Reading up on fabric softener. Sounds like it might weaken new
lines but adds strength (through lubrication) to older lines.
Founds a few quotes like this around the web:
"Tests by Smith (1988) indicate that treatment with concentrated fabric softener reduced the strength of a new rope but
Frank (1989) showed that certain ropes treated with dilute softener (per manufacturer’s recommendations) were stronger than the same rope without softening, after aging and washing.
Frank reported that the likely mechanism at work explaining these results, is that the fiber lubricants contained in new rope are lost with age, allowing the fibers to cut one another. Fabric softener replaces some of the lubricants. Excess softening leaves the rope effectively wet, with the corresponding loss in strength."
The NewEngland Ropes website says this:
http://www.neropes.com/LineCare.aspxDirt and salt can cause premature wear. Frequently wash rope and running rigging with fresh water. For a more thorough cleaning, soak your rope in warm water mixed with a mild detergent. Add a small amount of fabric softener to soften the rope. When possible, use a front loading washing machine; wash your rope in a mesh bag or pillowcase to avoid tangling. Rinse thoroughly and hang to dry in indirect sunlight. Note: the washing of new / unused rope should be performed by hand wash only.