Removing Mildew from Your Boat's Mooring Cover

By: David Thompson
Lightning Fleet 50

After six years, the Sunbrella^TM  mooring cover on our Lighting had a very substantial growth of ugly green and black mildew over a good portion of its surface, and we wanted very much to remove it.

It took a combination of a nice day with nothing better to do, plus an 80-gallon plastic tub (the one we use to hold ice and beer at our picnics); a cup of liquid laundry detergent; a cup of liquid Clorox;  40 gallons of hot water;  a hose with a nozzle and good water pressure;  a stiff-bristle scrub brush; a squirt bottle filled with Clorox; and about 4 hours of our time.

We did check with the cover's manufacturer first, who told us that the detergent, water, and Clorox mixture would be OK.

First we filled the tub half full with the hottest water we could draw from the laundry room, and added the liquid detergent and the Clorox.  then we hauled the tub out to the driveway and laid the mooring cover into the tub, making sure all of the cover's surfaces got wet.  Then we filled the tub with cold water from the garden hose, and used our arms to make a human washing machine agitator for a few minutes.

Then we let it sit for two hours and worked on other things.

Returning to the tub we agitated the contents for a few more minutes, then pulled the cover out and spread it flat on the driveway, with the outside, mildew-covered surface facing up.

The hot water, detergent, and Clorox may have killed the mildew, but it didn't do much to remove it from the cover.  That's where the stiff-bristle brush and the squirt bottle of Clorox came in.

We'd recommend using rubber gloves and eye protection, and wearing very old clothes when doing the next step.  We got down on our hands and knees, and working a section at a time, attacked each patch of mildew with the brush, squirting Clorox on the most stubborn spots, and then rinsing aggressively with the hose and nozzle set to the highest possible pressure  stream before moving on to the next section.  That was the hardest part of the work, and it took about half an hour to remove all the patches of mildew.

Next it was time for a couple of thorough rinsings.  We hosed the entire surface while the cover was on the driveway; then set it back in the (emptied out) tub, filled it to the brim with cold water, did the human washing machine agitation thing again, and let it sit for an hour.

Then we pulled it out of the tub, and hosed it off again, this time while it was hanging on the fence so that the rinse water would run right off.  We turned the cover over, to hose the inside surface, then let it sit on the fence in the breeze and sunshine until it was mostly dry.

And we should note that we dumped the waste water responsibly.

The result is a nice, clean, completely mildew-free cover.

We'll need to apply a water repellent before putting the cover back on the boat, and we are currently scouting the internet for a cost-effective product, and have already found a couple in the $60 per gallon price range.

All in all, if we only do this once every 6 years, it's not a bad task.

David