When I purchased our Oday in October 13, everything had green mildew and
black mold throughout. Deck surfaces, hull areas with mold, headliner and hidden spots in the cabin were treated with bleach, purple power and dawn liquid. Worked like magic. When I got the price for replacement of all the running rigging, I figured I could bring back most of the halyards and sheets to usefulness if I could remove the black and green accumulation they had grown. Using water with a liberal dose of Dawn liquid and approx. 4 tablespoons bleach per gallon (don't use too much), I soaked the lines for about three hours, periodically agitating them in the bucket about hourly. I immediately rinsed them very thoroughly in fresh water and rereigged them. The mainsheet, preventer, and three halyards at the main came beautifully clean and were soft enough to hand to be used and showed no signs of damage to the lines. The mizzen sheet was the first line I attempted to clean and the amount of bleach I used was considerably stronger in solution than I used later. The mizzen sheet came clean but the outer cover shredded and came apart as I rinsed it. Use sparing amounts of bleach and you should be fine. I think I saved about 600 dollars cleaning lines instead of replacing them.
Good luck,
Darrell