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Managing Mildew By Carolyn Corbett


t’s there...lurking in lockers, flourishing on fenders, prospering on papers. Mildew—the bane of the boater. It looks bad, smells nasty, aggravates allergies and causes damage to fabrics, electronics and metal components. Mildew spores exist virtually everywhere. They come aboard in the air. They thrive in the same range of temperature and humidity that people do. Commercial products promising a mildew-free future are a bit optimistic. Myrna Farquhar, a nurse/sailor from New York, reports that even autoclaves have trouble killing mildew spores. Cleansers containing a chlorine component will kill mildew, but if the accompanying residue is not completely eradicated, it reappears shortly, using the residue as nourishment. Fungicides aren’t the solution. They discourage growth temporarily, but often contain formaldehyde, phenol, pentachlorophenol, or kerosene. The “de-structions” on the label should be followed carefully. The bad news? Mildew is going to be around longer than we are. The good news? There are ways to control this culprit. Mildew Requires Four Things 1. The right temperature. Mildew prefers a balmy 77 to 88 degrees, but will grow at temps as low as 32 degrees and as high as 95. 2. Humidity. Moisture is mildew’s soulmate. The optimal growth range is 70 percent to 93 percent relative humidity. 3. Food. Any organic or bacterial material is sustenance— wood, paper, food, leather, natural fibers, smears from sticky fingers, damp swimsuits, soap scum in the shower—yum! 4. Oxygen. Let’s face it. Boats are mildew magnets. They

How Much Ventilation Is Required For Your Boat? Ideally, the air in the interior of a boat should be circulated once every hour. A typical 30-foot boat contains approximately 800 cubic feet of air. The general guidelines for providing maintenance ventilation are: Up to 24 feet: 1 exhaust vent 24 to 40 feet: 1 exhaust vent and 1 intake vent 40+ feet: 2 exhaust vents and 1 intake vent To specifically calculate your boat’s air volume, use this formula: A x B x C x 70% = Boat Interior Volume A: Interior length (excluding cockpit) B: Boat width C: Average interior height (This information was provided by the Nicro Ventilation Systems.) 54

November 2005


A solar vent, like this one by Nicro, is important in circulating fresh air into a boat.

generate moisture (condensation) due to disparities in water, air and hull temperatures. Interior and exterior temperatures are rarely identical and constantly fluctuate. Well-insulated vessels experience fewer problems since less condensation forms. A boat without proper ventilation is Home Sweet Home to mildew, yet ventilation during warm, humid periods actually fosters problems by allowing up to 20 gallons of moisture a day to enter a vessel. The purpose of ventilation is not simply to move air, but to equalize humidity levels inside and outside the boat. Powerful Weapons to Fight Mildew Solar vents use the sun’s energy to power fans, providing ventilation without drawing down your 12-volt supply. Cruisers who install solar-powered vents with rechargeable batteries battle fewer bouts with the pesky problem. Air conditioners remove moisture from the air as they cool it. Cool air holds less moisture than warm air, so liquid condenses on the cooling coils and runs to a drain. Dehumidifiers pull water out of the air in a similar manner, though there is little change in temperature. Some marine dehumidifiers have hoses. Cruisers on the hard often leave the sink thru hull open and allow the water to drip into the sink. Other models have collection pans that must be cleaned regularly can guess! Air purifying units with high efficiency particulate air (HEPA) filters remove mildew spores from the air. HEPA was developed by the U.S. Atomic Energy Commission to prevent radioactive particles from escaping into the atmosphere. A human hair is 300 times too big to go through a HEPA filter. Virtually any machine with a fan can call itself an air cleaner, though, so research before investing. Ozone generators duplicate the effects of the sun’s rays. Ozone is a form of oxygen that rapidly breaks down into oxygen molecules and atoms. The oxygen atoms eliminate odors, toxic gases, and the organic and bacterial matter that feeds mildew. The atoms are like tiny kamikaze pilots, defending every hard-to-reach nook and cranny on the boat They are going to die, but they’re taking mildew food with them when they go.