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The Ozone Zone

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An ozone generator can be connected to any existing water tank that has an access plate.

Any shellback will tell you that ships don't run on diesel, they run on coffee. If the coffee's no good, the ship won't be a happy one. And the coffee won't be good unless the water that brews it is good—free of unpleasant tastes and odors that make a cuppa Joe punishment, not pleasure. But is any water on the planet less tasty than H2O stored in a boat's freshwater tanks? I don't think so. Fortunately Ken Hughes has a solution.

Hughes is owner and president of Chem-Free Water Treatment Systems in Decatur, Texas. His system uses an onboard ozone generator to supply a diffuser in the bottom of a freshwater tank. Ozone bubbles out of the diffuser and up through the water, killing bacteria and disinfecting as it goes. (It's similar to the aerator in an aquarium.) The water absorbs a little ozone, which eventually finds its way overboard through the tank's vent; once in fresh air, ozone quickly degrades into oxygen. (An ozone molecule is an oxygen molecule with an extra oxygen atom attached—O3 rather than O2.) Unless you stick your nose right under the vent, you'll never smell the ozone, but you'll taste its effect: Ozone-treated water will be clear, clean, and odor-free. A Chem-Free system can be retrofitted to almost any tank, even those full of water.

Hughes has been building Chem-Free Water Quality Assurance (WQA) systems since 1993. Today they are used aboard yachts as well as commercial and research vessels, including those operated by Woods Hole Oceanographic Institution, Scripps Institution of Oceanography , and others. But treating water with ozone isn't a new idea; the process has been used for more than 100 years by municipal water systems, starting in Nice, France, in 1906. Since then many cities in the United States and abroad have replaced chlorination water treatment systems with ozonation because it's not only safer for humans but less harmful to the environment.


This Corona unit treats holding tanks.

Ozone's use as a water purifier doesn't end in the freshwater tank: It will also keep sea chests clean. Marine life—flora and fauna—can get into the sea chest and thrive, eventually clogging the water pickups. (Fish larva often swim through the screen and grow until the fish are too big to swim out.) Chem-Free's Sea-Chest Guardian system draws water out of the sea chest, treats it with ozone to kill unwanted sea life, then reintroduces it into the sea chest before the chest becomes an underwater fish zoo. The Guardian's ozone generator can supply ozone to fight unpleasant odors in grey- and black-water tanks, too: The gas is simply piped into the headspace of the tanks.

For more information on any Chem-Free product, contact Ken Hughes at (940) 627-7879, or visit You'll probably catch him enjoying a tasty cup of coffee.


On a hot day last summer, I noticed bubbling around the deck plate on my holding-tank pumpout. It did not smell good, either. I pumped the tank, and the problem went away for a while but came back. How can I fix it for good?—E. Scrooge, via e-mail

You have two problems. First, your deck-plate cap is leaking, probably because its O-ring or gasket is damaged or worn out. Remove the cap, and lift the O-ring out of its groove or pull off the gasket. (Most caps nowadays use O-rings.) Clean under the O-ring/gasket. But before buying a replacement, check all your deck-plate caps; if one is bad, maybe others are, too.

Coat the O-ring lightly with grease, keeping it clean of grit or other contaminants, then stretch it over the cap, and slip it into its groove without twisting or kinking it. You'll find the cap harder to screw down than before because of the new O-ring. Repeat the process on all other deck-plate caps.

You probably have a clogged holding-tank vent, too, a by-product of not pumping out the tank regularly. Solid waste gets into the vent fitting on the tank; air pressure, caused by waste breakdown and exacerbated by a hot summer day, can't get out through the clogged vent, so it finds any other exit, including a leaky deck plate. In extreme circumstances the pressure will crack fittings or even split hoses or the tank itself. Clean the vent by disassembling it completely, from the tank to the hull. There's a check valve in the fitting on the tank; that's where the clog usually is. It's easier to replace the fitting than clean it, but if you insist, remove the gunk the best way you can. Replace the vent hose, too, while you're at it, and the in-line filter if you have one. Next year pump out your tank more often.

This article originally appeared in the December 2007 issue of Power & Motoryacht magazine.