I have had reasonable results soaking halyards & other control lines in water
& napisan. I left it for a few days in a big plastic bin stiring occasionaly as walked by before giving them a good rinse with the garden hose before putting them in the washing
machine with some wool wash or fabric
softner. Amazing how much dirt came out.
will get pretty tangled during the was cycle - you could put it into one of those mesh washing
bags if you want.
Best do this when the wife is not around...
Don't expect them to be as new, but they do look better & do become a fair bit softer (ie they run lot better).
Not sure what effect the bleach in the napisan has on the strength of the rope
- but our stuff is holding up well so far.