I find the power washer does a nice job on mooring bridles and pennants between seasons, or other dirty lines. I lay them out on the driveway and blast 90% of the slime and growth off.

I cover the portions that are constantly in the water with split foam pipe insulation so they don't sink and wrap beneath the mooring, but by covering the whole sections that are constantly touching the water they are also protected from hard growth. I replace the insulation each year. It's only a few bucks at Home Depot plumbing dept.